Type Safe C++? - LOL! :-)

So called "strong types", genuinely type safe alternatives to "typedef:s" are often seen as a way to prevent bugs, but they can also be used to improve clarity in your code, and even increase performance. It is underappreciated how strong the type safety guarantees in C++ are, because it takes knowledge and a bit of discipline to make use of it.

In this session, I give motivating examples for why strong types are good, and present some of the techniques for creating them. The simplest techniques requires no library support, but I will also show some more sophisticated solutions from open source libraries available on github. We will go through what happens with both production code and test code when you use them, and also discuss the pros and cons of the different approaches.

Transcript

1. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 1/144
   Type Safe C++? - LOL! :-)
   Björn Fahller
   

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2. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 2/144
   Type Safe C++? - LOL! :-)
   Björn Fahller
   

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3. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 3/144
   Type Safe C++? - LOL! :-)
   What is type safety?
   

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4. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 4/144
   What is type safety?
   type safety (Noun)
   the extent to which a programming language
   discourages or prevents type errors
   -- Wiktionary
   

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5. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 5/144
   A type safe system discourages or prevents...
   ●
   ... use of one type when another is intended
   ●
   ... operations that do not make sense
   ●
   ... use of values outside the defined space
   

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6. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 6/144
   ●
   Introduction to type safety
   ●
   Type safety in C++
   ●
   Simple library solution for strong types
   ●
   Sophisticated libraries – scouting github!
   ●
   What strong types does with your code
   Type Safe C++? - LOL! :-)
   

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7. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 7/144
   using request_id = uint32_t;
   using receiver_id = uint32_t;
   token remove(request_id req, receiver_id rec);
   token initiate_remove(receiver_id receiver)
   {
   auto req = new_request();
   return remove(receiver, req);
   }
   My story begins
   

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8. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 8/144
   using request_id = uint32_t;
   using receiver_id = uint32_t;
   token remove(request_id req, receiver_id rec);
   token initiate_remove(receiver_id receiver)
   {
   auto req = new_request();
   return remove(receiver, req);
   }
   My story begins
   

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9. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 9/144
   using request_id = uint32_t;
   using receiver_id = uint32_t;
   token remove(request_id req, receiver_id rec);
   token initiate_remove(receiver_id receiver)
   {
   auto req = new_request();
   return remove(receiver, req);
   }
   My story begins
   

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10. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 10/144
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    When is
    this call
    allowed?
    

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11. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 11/144
    using A = double;
    using B = enum { aa, bb, cc };
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    

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12. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 12/144
    struct A {
    int value;
    };
    struct B {
    int value;
    };
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    

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13. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 13/144
    struct A {
    int value;
    };
    struct B {
    int value;
    };
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    If we want this to compile, we can add:
    

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14. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 14/144
    struct A {
    int value;
    };
    struct B {
    int value;
    };
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    If we want this to compile, we can add:
    A::A(B const&); // not explicit
    

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15. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 15/144
    struct A {
    int value;
    };
    struct B {
    int value;
    };
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    If we want this to compile, we can add:
    A::A(B const&); // not explicit
    B::operator A(); // not explicit
    

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16. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 16/144
    struct A {
    int value;
    };
    struct B {
    int value;
    };
    void other(A const& a);
    void func(B b)
    {
    other(b);
    }
    If we want this to compile, we can add:
    A::A(B const&); // not explicit
    B::operator A(); // not explicit
    A as a public base class to B
    

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17. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 17/144
    struct request_id { uint32_t value; };
    struct receiver_id { uint32_t value; };
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    request_id req = new_request();
    return remove(receiver, req);
    }
    A different story begins
    

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18. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 18/144
    struct request_id { uint32_t value; };
    struct receiver_id { uint32_t value; };
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    request_id req = new_request();
    return remove(receiver, req);
    }
    error: no matching function for call to 'remove'
    return remove(receiver, req);
    ^~~~~~
    note: candidate function not viable:
    no known conversion from 'receiver_id' to 'request_id' for 1st argument
    token remove(request_id req, receiver_id rec);
    ^
    

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19. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 19/144
    We have control over
    when the compiler
    will allow a conversion!
    

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20. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 20/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    private:
    uint32_t value;
    };
    

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21. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 21/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    private:
    uint32_t value;
    };
    

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22. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 22/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    

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23. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 23/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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24. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 24/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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25. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 25/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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26. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 26/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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27. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 27/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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28. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 28/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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29. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 29/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    

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30. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 30/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    There’s an awful
    lot of boiler plate
    code here!
    

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31. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 31/144
    class receiver_id
    {
    public:
    explicit receiver_id(uint32_t v) : value{v} {}
    operator uint32_t() const { return value; }
    bool operator==(receiver_id v) const {
    return value == v.value;
    }
    bool operator!=(receiver_id v) const;
    bool operator...
    private:
    uint32_t value;
    };
    There’s an awful
    lot of boiler plate
    code here!
    Repeat once more
    for request_id
    

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32. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 32/144
    ●
    Introduction to type safety
    ●
    Type safety in C++
    ●
    Simple library solution for strong types
    ●
    Sophisticated libraries – scouting github!
    ●
    What strong types does with your code
    Type Safe C++? - LOL! :-)
    

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33. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 33/144
    template
    class safe_type
    {
    public:
    private:
    T value_;
    };
    

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34. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 34/144
    template
    class safe_type
    {
    public:
    safe_type(T t) : value_(std::move(t)) {}
    operator T() const { return value_; }
    // operators...
    private:
    T value_;
    };
    

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35. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 35/144
    template
    class safe_type
    {
    public:
    safe_type(T t) : value_(std::move(t)) {}
    template
    safe_type(safe_type const&) = delete;
    operator T() const { return value_; }
    // operators...
    private:
    T value_;
    };
    

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36. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 36/144
    template
    class safe_type
    {
    public:
    safe_type(T t) : value_(std::move(t)) {}
    template
    safe_type(safe_type const&) = delete;
    operator T() const { return value_; }
    // operators...
    private:
    T value_;
    };
    using int1 = safe_type;
    using int2 = safe_type;
    

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37. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 37/144
    using request_id = safe_type;
    using receiver_id = safe_type;
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    

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38. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 38/144
    using request_id = safe_type;
    using receiver_id = safe_type;
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    

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39. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 39/144
    using request_id = safe_type;
    using receiver_id = safe_type;
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    

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40. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 40/144
    using request_id = safe_type;
    using receiver_id = safe_type;
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    error: no matching function for call to 'remove'
    remove(receiver, req);
    ^~~~~~
    note: candidate function not viable: no known conversion
    from 'safe_type'
    to 'safe_type' for 1st argument
    token remove(request_id req, receiver_id rec);
    ^
    

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41. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 41/144
    using request_id = safe_type;
    using receiver_id = safe_type;
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    

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42. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 42/144
    struct request_id : safe_type {
    using safe_type::safe_type;
    };
    struct receiver_id : safe_type {
    using safe_type::safe_type;
    };
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    

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43. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 43/144
    struct request_id : safe_type {
    using safe_type::safe_type;
    };
    struct receiver_id : safe_type {
    using safe_type::safe_type;
    };
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    error: no matching function for call to 'remove'
    remove(receiver, req);
    ^~~~~~
    note: candidate function not viable: no known conversion
    from 'receiver_id' to 'request_id' for 1st argument
    token remove(request_id req, receiver_id rec);
    ^
    

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44. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 44/144
    struct request_id : safe_type {
    using safe_type::safe_type;
    };
    struct receiver_id : safe_type {
    using safe_type::safe_type;
    };
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    #define SAFE_TYPE(name, base_type) \
    struct name : safe_type { \
    using safe_type::safe_type; \
    }
    

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45. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 45/144
    SAFE_TYPE(request_id, uint32_t);
    SAFE_TYPE(receiver_id, uint32_t);
    token remove(request_id req, receiver_id rec);
    token initiate_remove(receiver_id receiver)
    {
    auto req = new_request();
    return remove(receiver, req);
    }
    #define SAFE_TYPE(name, base_type) \
    struct name : safe_type { \
    using safe_type::safe_type; \
    }
    

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46. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 46/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    

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47. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 47/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    

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48. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 48/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidental swap!
    

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49. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 49/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    

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50. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 50/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    template
    struct safe_type : T
    {
    using T::T;
    template
    safe_type(safe_type const&) = delete;
    };
    

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51. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 51/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidental swap!
    error: no matching function for call to 'label_interface'
    label_interface(customer, if_name);
    ^~~~~~~~~~~~~~~
    note: candidate function not viable: no known conversion
    from 'customer_name'
    to 'const interface_name' for 1st argument
    void label_interface(const interface_name& ifname,
    ^
    

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52. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 52/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    template
    struct safe_type : T
    {
    using T::T;
    template
    safe_type(safe_type const&) = delete;
    };
    

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53. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 53/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    template
    struct safe_type : T
    {
    using T::T;
    template
    safe_type(safe_type const&) = delete;
    };
    

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54. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 54/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    template
    struct safe_type : T
    {
    using T::T;
    template
    safe_type(safe_type const&) = delete;
    };
    Oh, no, I violated the
    Liskov Substitution Principle!
    

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55. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 55/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    template
    struct safe_type : T
    {
    using T::T;
    template
    safe_type(safe_type const&) = delete;
    };
    Liskov Substitution Principle
    Subtype Requirement:
    Let φ(x) be a property provable about objects x of type T.
    Then φ(y) should be true for objects y of type S
    where S is a subtype of T.
    

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56. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 56/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    const customer_name& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Accidertal swap!
    template typename tag,
    bool = std::is_class{} && !std::is_final{}>
    class safe_type { /* as before */};
    template
    struct safe_type : T
    {
    using T::T;
    template
    safe_type(safe_type const&) = delete;
    };
    Liskov Substitution Principle
    Subtype Requirement:
    Let φ(x) be a property provable about objects x of type T.
    Then φ(y) should be true for objects y of type S
    where S is a subtype of T.
    Robert (Uncle Bob) Martin
    Functions that use pointers or references
    to base classes must be able to use objects
    of derived classes without knowing it.
    

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57. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 57/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Liskov Substitution Principle
    Subtype Requirement:
    Let φ(x) be a property provable about objects x of type T.
    Then φ(y) should be true for objects y of type S
    where S is a subtype of T.
    Robert (Uncle Bob) Martin
    Functions that use pointers or references
    to base classes must be able to use objects
    of derived classes without knowing it.
    customer_name and interface_name
    are different types implemented in terms
    of strings
    

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58. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 58/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Liskov Substitution Principle
    Subtype Requirement:
    Let φ(x) be a property provable about objects x of type T.
    Then φ(y) should be true for objects y of type S
    where S is a subtype of T.
    Robert (Uncle Bob) Martin
    Functions that use pointers of reference
    to base classes must be able to use objects
    of derived classes without knowing it.
    customer_name and interface_name
    are different types implemented in terms
    of strings
    

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59. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 59/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Liskov Substitution Principle
    Subtype Requirement:
    Let φ(x) be a property provable about objects x of type T.
    Then φ(y) should be true for objects y of type S
    where S is a subtype of T.
    Robert (Uncle Bob) Martin
    Functions that use pointers of reference
    to base classes must be able to use objects
    of derived classes without knowing it.
    customer_name and interface_name
    are different types implemented in terms
    of strings, but they are not strings.
    

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60. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 60/144
    SAFE_TYPE(interface_name, std::string);
    SAFE_TYPE(customer_name, std::string);
    void label_interface(interface_name const& ifname,
    customer_name const& customer);
    interface_name lookup_interface(MAC_address mac);
    void setup_customer(MAC_address mac,
    customer_name const& customer)
    {
    assert(!customer.empty());
    auto if_name = lookup_interface(mac);
    assert(if_name.find(':') != std::string::npos);
    label_interface(customer, if_name);
    }
    Liskov Substitution Principle
    Subtype Requirement:
    Let φ(x) be a property provable about objects x of type T.
    Then φ(y) should be true for objects y of type S
    where S is a subtype of T.
    Robert (Uncle Bob) Martin
    Functions that use pointers of reference
    to base classes must be able to use objects
    of derived classes without knowing it.
    customer_name and interface_name
    are different types implemented in terms
    of strings, but they are not strings.
    Maybe it makes sense to allow unlimited access
    to the non-mutating functions of
    std::string, but not to all mutating ones.
    

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61. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 61/144
    ●
    Introduction to type safety
    ●
    Type safety in C++
    ●
    Simple library solution for strong types
    ●
    Sophisticated libraries – scouting github!
    ●
    What strong types does with your code
    Type Safe C++? - LOL! :-)
    

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62. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 62/144
    Jonathan Müller @foonathan
    type_safe Zero overhead utilities for
    preventing bugs at compile time
    https://github.com/foonathan/type_safe
    

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63. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 63/144
    Jonathan Müller @foonathan
    type_safe Zero overhead utilities for
    preventing bugs at compile time
    https://github.com/foonathan/type_safe
    A rich type library, with which you can piece together the exact behaviour
    of a type that you want.
    It also includes a number of predefined neat type templates, and other
    features like improved optional and variant
    

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64. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 64/144
    Jonathan Müller @foonathan
    type_safe Zero overhead utilities for
    preventing bugs at compile time
    https://github.com/foonathan/type_safe
    A rich type library, with which you can piece together the exact behaviour
    of a type that you want.
    It also includes a number of predefined neat type templates, and other
    features like improved optional and variant
    Since October 2016
    

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65. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 65/144
    // type_safe/strong_typedef.hpp
    template
    class type_safe::strong_typedef {
    public:
    constexpr strong_typedef();
    explicit constexpr strong_typedef(const T& value);
    explicit constexpr strong_typedef(T&& value);
    explicit constexpr operator T&() & noexcept;
    explicit constexpr operator const T&() const & noexcept;
    explicit constexpr operator T&&() && noexcept;
    explicit constexpr operator const T&&() const && noexcept;
    };
    https://github.com/foonathan/type_safe
    

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66. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 66/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    , op::output_operator
    {
    using strong_typedef::strong_typedef;
    };
    struct my_int : ts::strong_typedef
    , op::integer_arithmetic
    {
    using strong_typedef::strong_typedef;
    };
    

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67. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 67/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    , op::output_operator
    {
    using strong_typedef::strong_typedef;
    };
    struct my_int : ts::strong_typedef
    , op::integer_arithmetic
    {
    using strong_typedef::strong_typedef;
    };
    

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68. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 68/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    , op::output_operator
    {
    using strong_typedef::strong_typedef;
    };
    struct my_int : ts::strong_typedef
    , op::integer_arithmetic
    {
    using strong_typedef::strong_typedef;
    };
    

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69. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 69/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    , op::output_operator
    {
    using strong_typedef::strong_typedef;
    };
    struct my_int : ts::strong_typedef
    , op::integer_arithmetic
    {
    using strong_typedef::strong_typedef;
    };
    

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70. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 70/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    , op::output_operator
    {
    using strong_typedef::strong_typedef;
    };
    struct my_int : ts::strong_typedef
    , op::integer_arithmetic
    {
    using strong_typedef::strong_typedef;
    };
    

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71. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 71/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    , op::output_operator
    {
    using strong_typedef::strong_typedef;
    };
    struct my_int : ts::strong_typedef
    , op::integer_arithmetic
    {
    using strong_typedef::strong_typedef;
    };
    

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72. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 72/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    {
    using strong_typedef::strong_typedef;
    friend std::ostream&
    operator<{
    return os << "H{" << static_cast(h) << "}";
    }
    };
    

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73. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 73/144
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    , op::equality_comparison
    {
    using strong_typedef::strong_typedef;
    friend std::ostream&
    operator<{
    return os << "H{" << ts::get(h) << "}";
    }
    };
    

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74. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 74/144
    Jonathan Boccara @joboccara
    NamedType Implementation of
    strong types in C++
    https://github.com/joboccara/NamedType
    

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75. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 75/144
    Jonathan Boccara @joboccara
    NamedType Implementation of
    strong types in C++
    https://github.com/joboccara/NamedType
    A small type library with a simpler aim, but which still allows you to
    piece together the strong types with your desired behaviour.
    It also supports conversions between different types of the same kind,
    for example meters to feet, or non-linear like Watt to dB.
    

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76. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 76/144
    Jonathan Boccara @joboccara
    NamedType Implementation of
    strong types in C++
    https://github.com/joboccara/NamedType
    A small type library with a simpler aim, but which still allows you to
    piece together the strong types with your desired behaviour.
    It also supports conversions between different types of the same kind,
    for example meters to feet, or non-linear like Watt to dB.
    MeetingC++ https://www.youtube.com/watch?v=WVleZqzTw2k
    

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77. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 77/144
    // NamedType/named_type.hpp
    using my_handle =
    fluent::NamedType<
    int, struct my_handle_tag
    >;
    https://github.com/joboccara/NamedType
    

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78. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 78/144
    // NamedType/named_type.hpp
    using my_handle =
    fluent::NamedType<
    int, struct my_handle_tag,
    fluent::comparable,
    fluent::printable,
    fluent::hashable
    >;
    https://github.com/joboccara/NamedType
    

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79. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 79/144
    // NamedType/named_type.hpp
    struct my_handle
    : fluent::NamedType<
    int, my_handle,
    fluent::comparable,
    fluent::printable,
    fluent::hashable
    >
    {
    using NamedType::NamedType;
    };
    https://github.com/joboccara/NamedType
    

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80. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 80/144
    // NamedType/named_type.hpp
    struct my_handle
    : fluent::NamedType<
    int, my_handle,
    fluent::comparable,
    fluent::printable,
    fluent::hashable,
    fluent::ImplicitlyConvertibleTo::templ
    >
    {
    using NamedType::NamedType;
    };
    https://github.com/joboccara/NamedType
    

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81. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 81/144
    ●
    Introduction to type safety
    ●
    Type safety in C++
    ●
    Simple library solution for strong types
    ●
    Sophisticated libraries – scouting github!
    ●
    What strong types does with your code
    Type Safe C++? - LOL! :-)
    

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82. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 82/144
    Network capacity utilisation
    0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
    Frame with 24 slots
    A slot is a network capacity quanta
    

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83. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 83/144
    Network capacity utilisation
    0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
    Frame with 24 slots
    SlotCount SlotIndexes SlotRanges
    8 3,4,7,8,13,14,15,16 {3-4},{7-8},{13-16}
    3 5,9,10 {5},{9-10}
    13 0,1,2,6,11,12,17,18,
    19,20,21,22,23
    {0-2},{6},{11-12},{17-23}
    A slot is a network capacity quanta
    

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84. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 84/144
    Network capacity utilisation
    0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
    Frame with 24 slots
    SlotCount SlotIndexes SlotRanges
    8 3,4,7,8,13,14,15,16 {3-4},{7-8},{13-16}
    3 5,9,10 {5},{9-10}
    13 0,1,2,6,11,12,17,18,
    19,20,21,22,23
    {0-2},{6},{11-12},{17-23}
    A slot is a network capacity quanta
    typename SlotIndex; typename SlotCount; struct SlotRange {
    SlotIndex start;
    SlotCount length;
    };
    

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85. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 85/144
    Magic Numbers
    

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86. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 86/144
    SlotCount availableCapacity();
    ...
    if (availableCapacity() == 0) {
    ...
    }
    

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87. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 87/144
    SlotCount availableCapacity();
    ...
    if (availableCapacity() == SlotCount{0}) {
    ...
    }
    

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88. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 88/144
    SlotCount availableCapacity();
    constexpr SlotCount noSlots{0};
    ...
    if (availableCapacity() == noSlots) {
    ...
    }
    

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89. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 89/144
    Encapsulation
    

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90. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 90/144
    class MessageBuffer
    {
    public:
    template
    void serialize_bits(unsigned value);
    };
    SlotCount capacity = ...
    MessageBuffer buffer ...
    buffer.serialize_bits<24>(capacity);
    

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91. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 91/144
    class MessageBuffer
    {
    public:
    template
    void serialize_bits(unsigned value);
    };
    SlotCount capacity = ...
    MessageBuffer buffer ...
    buffer.serialize_bits<24>(capacity);
    

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92. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 92/144
    class MessageBuffer
    {
    public:
    template
    void serialize_bits(unsigned value);
    };
    void serialize_data(MessageBuffer& b, SlotCount const& c)
    {
    b.serialize_bits<24>(c);
    }
    SlotCount capacity = ...
    MessageBuffer buffer ...
    serialize_data(buffer, capacity);
    

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93. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 93/144
    class MessageBuffer
    {
    public:
    template
    void serialize(T const& t) { serialize_data(*this, t); }
    template
    void serialize_bits(unsigned value);
    };
    void serialize_data(MessageBuffer& b, SlotCount const& c)
    {
    b.serialize_bits<24>(c);
    }
    SlotCount capacity = ...
    MessageBuffer buffer ...
    buffer.serialize(capacity);
    

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94. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 94/144
    Type Semantics
    

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95. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 95/144
    class SlotPool
    {
    public:
    void releaseCapacity(std::vector const& ranges)
    SlotCount availableCapacity() const { return unusedSlots;}
    ...
    private:
    SlotCount unusedSlots;
    ...
    };
    

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96. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 96/144
    class SlotPool
    {
    public:
    void releaseCapacity(std::vector const& ranges)
    {
    for (auto& range : ranges)
    {
    ususedSlots += range.length;
    }
    ...
    }
    SlotCount availableCapacity() const { return unusedSlots;}
    ...
    private:
    SlotCount unusedSlots;
    ...
    };
    

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97. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 97/144
    class SlotPool
    {
    public:
    void releaseCapacity(std::vector const& ranges)
    {
    for (auto& range : ranges)
    {
    ususedSlots += range.length;
    }
    ...
    }
    SlotCount availableCapacity() const { return unusedSlots;}
    ...
    private:
    SlotCount unusedSlots;
    ...
    };
    Does not compile!
    No operator += for SlotCount
    

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98. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 98/144
    Which operations makes sense?
    SlotCount+SlotCount?
    0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
    Frame with 24 slots
    

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99. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 99/144
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
    Frame with 24 slots
    

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100. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 100/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

101. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 101/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

102. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 102/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

103. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 103/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

104. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 104/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

105. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 105/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

106. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 106/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

107. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 107/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

108. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 108/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

109. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 109/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

110. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 110/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

111. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 111/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

112. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 112/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

113. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 113/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

114. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 114/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

115. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 115/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

116. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 116/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

117. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 117/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

118. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 118/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

119. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 119/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

120. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 120/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

121. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 121/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

122. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 122/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

123. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 123/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

124. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 124/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex
     SlotIndex*SlotCount?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

125. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 125/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex
     SlotIndex*SlotCount
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

126. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 126/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex
     SlotIndex*SlotCount
     SlotIndex*Ratio?
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

127. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 127/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex
     SlotIndex*SlotCount
     SlotIndex*Ratio
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

     View Slide

128. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 128/144
     Which operations makes sense?
     SlotCount+SlotCount->SlotCount
     SlotCount-SlotCount->SlotCount
     SlotCount*SlotCount
     SlotCount*Ratio->SlotCount
     SlotCount/SlotCount->Ratio
     SlotCount/Ratio->SlotCount
     SlotIndex+SlotIndex
     SlotIndex+SlotCount->SlotIndex
     SlotIndex-SlotIndex->SlotCount
     SlotIndex/SlotIndex
     SlotIndex/SlotCount
     SlotIndex/Ratio
     SlotIndex*SlotIndex
     SlotIndex*SlotCount
     SlotIndex*Ratio
     Affine Space
     In mathematics, an affine space is a geometric
     structure that generalizes the properties of Euclidean
     spaces in such a way that these are independent of
     the concepts of distance and measure of angles,
     keeping only the properties related to parallelism and
     ratio of lengths for parallel line segments...
     -- Wikipedia
     0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223
     Frame with 24 slots
     

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129. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 129/144
     Test Code
     

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130. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 130/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     DestClient client1 = node.clientWithCapacity(5);
     DestClient client2 = node.clientWithCapacity(8);
     REQUIRE_CALL(client1, newCapacity(4, 2));
     REQUIRE_CALL(client2, newCapacity(4, 3));
     node.throttleCapacityTo(4, 5);
     }
     

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131. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 131/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     DestClient client1 = node.clientWithCapacity(5);
     DestClient client2 = node.clientWithCapacity(8);
     RequestId req{4};
     REQUIRE_CALL(client1, newCapacity(req, 2));
     REQUIRE_CALL(client2, newCapacity(req, 3));
     node.throttleCapacityTo(req, 5);
     }
     

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132. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 132/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     SlotCount c1Capacity{5}, c2Capacity{8};
     DestClient client1 = node.clientWithCapacity(c1Capacity);
     DestClient client2 = node.clientWithCapacity(c2Capacity);
     RequestId req{4};
     SlotCount newC1Capacity{2}, newC2Capacity{3};
     REQUIRE_CALL(client1, newCapacity(req, newC1Capacity));
     REQUIRE_CALL(client2, newCapacity(req, newC2Capacity));
     SlotCount newTotalCapacity{5};
     node.throttleCapacityTo(req, newTotalCapacity);
     }
     

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133. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 133/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     SlotCount c1Capacity{5}, c2Capacity{8};
     DestClient client1 = node.clientWithCapacity(c1Capacity);
     DestClient client2 = node.clientWithCapacity(c2Capacity);
     RequestId req{4};
     SlotCount newC1Capacity{2}, newC2Capacity{3};
     REQUIRE_CALL(client1, newCapacity(req, newC1Capacity));
     REQUIRE_CALL(client2, newCapacity(req, newC2Capacity));
     SlotCount newTotalCapacity{5};
     node.throttleCapacityTo(req, newTotalCapacity);
     }
     WTF!
     

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134. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 134/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     DestClient client1 = node.clientWithCapacity(SlotCount{5});
     DestClient client2 = node.clientWithCapacity(SlotCount{8});
     RequestId req{4};
     REQUIRE_CALL(client1, newCapacity(req, SlotCount{2}));
     REQUIRE_CALL(client2, newCapacity(req, SlotCount{3}));
     node.throttleCapacityTo(req, SlotCount{5});
     }
     

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135. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 135/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     DestClient client1 = node.clientWithCapacity(SlotCount{5});
     DestClient client2 = node.clientWithCapacity(SlotCount{8});
     RequestId req{4};
     REQUIRE_CALL(client1, newCapacity(req, SlotCount{2}));
     REQUIRE_CALL(client2, newCapacity(req, SlotCount{3}));
     node.throttleCapacityTo(req, SlotCount{5});
     }
     constexpr SlotCount operator"" _slots(unsigned long long v)
     {
     auto cv = static_cast(v);
     return SlotCount{cv};
     }
     

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136. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 136/144
     DestClient::newCapacity(RequestId, SlotCount);
     TestNode::throttleCapacityTo(RequestId, SlotCount total);
     TEST(capacity_decrease_is_notified_to_clients) {
     TestNode node;
     DestClient client1 = node.clientWithCapacity(5_slots);
     DestClient client2 = node.clientWithCapacity(8_slots);
     RequestId req{4};
     REQUIRE_CALL(client1, newCapacity(req, 2_slots));
     REQUIRE_CALL(client2, newCapacity(req, 3_slots));
     node.throttleCapacityTo(req, 5_slots);
     }
     constexpr SlotCount operator"" _slots(unsigned long long v)
     {
     auto cv = static_cast(v);
     return SlotCount{cv};
     }
     

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137. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 137/144
     ●
     Introduction to type safety
     ●
     Type safety in C++
     ●
     Simple library solution for strong types
     ●
     Sophisticated libraries – scouting github!
     ●
     What strong types does with your code
     Type Safe C++? - LOL! :-)
     

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138. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 138/144
     ●
     Safety for built in types is abysmal in C++
     Type Safe C++? - LOL! :-)
     

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139. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 139/144
     ●
     Safety for built in types is abysmal in C++
     ●
     Structs/classes are as strong as you wish
     – You must add the functionality you want
     Type Safe C++? - LOL! :-)
     

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140. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 140/144
     ●
     Safety for built in types is abysmal in C++
     ●
     Structs/classes are as strong as you wish
     – You must add the functionality you want
     ●
     Libraries exist that makes this easier
     Type Safe C++? - LOL! :-)
     

     View Slide

141. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 141/144
     ●
     Safety for built in types is abysmal in C++
     ●
     Structs/classes are as strong as you wish
     – You must add the functionality you want
     ●
     Libraries exist that makes this easier
     ●
     Thinking about what operations your types should support makes you understand the
     problem better!
     – Beware of the urge for convencience!
     Type Safe C++? - LOL! :-)
     

     View Slide

142. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 142/144
     ●
     Safety for built in types is abysmal in C++
     ●
     Structs/classes are as strong as you wish
     – You must add the functionality you want
     ●
     Libraries exist that makes this easier
     ●
     Thinking about what operations your types should support makes you understand the
     problem better!
     – Beware of the urge for convencience!
     ●
     Strong types leads to more expressive code
     – Fewer magical numbers
     – More encapsulation
     – Explicit tests that express intent
     Type Safe C++? - LOL! :-)
     

     View Slide

143. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 143/144
     ●
     Safety for built in types is abysmal in C++
     ●
     Structs/classes are as strong as you wish
     – You must add the functionality you want
     ●
     Libraries exist that makes this easier
     ●
     Thinking about what operations your types should support makes you understand the
     problem better!
     – Beware of the urge for convencience!
     ●
     Strong types leads to more expressive code
     – Fewer magical numbers
     – More encapsulation
     – Explicit tests that express intent
     Type Safe C++? - LOL! :-)
     Avoid typedef
     

     View Slide

144. Type Safe C++? - LOL! :-) – ACCU 2018 – © Björn Fahller @bjorn_fahller 144/144
     Björn Fahller
     bjorn@fahller.se
     @bjorn_fahller
     @rollbear cpplang, swedencpp
     Type Safe C++? - LOL! :-)
     

     View Slide