NDC{Oslo} Type safe C++? - LOL!

So called "strong types" are a way to reduce bugs and improve clarity in your code. It is underappreciated how strong the type safety guarantees of C++ are, because it takes knowledge and discipline to make use of it. Doing so, however, will not only make your code clearer, and prevents stupid bugs, it can also improve performance.

The simplest techniques for strong types requires no library support, but a number of more sophisticated solutions are available on github as open source libraries.

In this session I give some motivating examples and present some of the techniques for creating strong types. 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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 1/128
   Type Safe C++? - LOL! :-)
   Björn Fahller
   

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2. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 2/128
   Type Safe C++? - LOL! :-)
   Björn Fahller
   

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3. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 3/128
   Type Safe C++? - LOL! :-)
   What is type safety?
   

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4. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 4/128
   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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 5/128
   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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 6/128
   ●
   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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 7/128
   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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 8/128
   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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 9/128
   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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 10/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 11/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 12/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 13/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 14/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 15/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 16/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 17/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 18/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 19/128
    We have control over
    when the compiler
    will allow a conversion!
    

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20. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 20/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 21/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 22/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    

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23. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 23/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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24. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 24/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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25. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 25/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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26. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 26/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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27. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 27/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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28. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 28/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    enum class receiver_id : uint32_t {};
    

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29. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 29/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    

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30. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 30/128
    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<(receiver_id v) const;
    ...
    private:
    uint32_t value;
    };
    There’s an awful
    lot of boiler plate
    code here!
    

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31. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 31/128
    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<(receiver_id v) const;
    ...
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 32/128
    ●
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 33/128
    template
    class safe_type
    {
    public:
    private:
    T value_;
    };
    

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34. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 34/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 35/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 36/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 37/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 38/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 39/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 40/128
    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<[...], struct receiver_id_tag>'
    to 'safe_type<[...], struct request_id_tag>' for 1st argument
    token remove(request_id req, receiver_id rec);
    ^
    

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41. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 41/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 42/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 43/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 44/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 45/128
    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! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 46/128
    ●
    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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47. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 47/128
    Jonathan Müller @foonathan
    type_safe Zero overhead utilities for
    preventing bugs at compile time
    https://github.com/foonathan/type_safe
    

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48. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 48/128
    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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49. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 49/128
    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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50. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 50/128
    // 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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51. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 51/128
    https://github.com/foonathan/type_safe
    #include
    

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52. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 52/128
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    

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53. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 53/128
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    struct my_handle : ts::strong_typedef
    {
    using strong_typedef::strong_typedef;
    };
    

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54. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 54/128
    https://github.com/foonathan/type_safe
    #include
    namespace ts = type_safe;
    namespace op = type_safe::strong_typedef_op;
    struct my_handle : ts::strong_typedef
    {
    using strong_typedef::strong_typedef;
    };
    

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55. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 55/128
    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;
    };
    

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56. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 56/128
    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;
    };
    

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57. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 57/128
    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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58. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 58/128
    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<<(std::ostream& os, my_handle const& h)
    {
    return os << "H{" << static_cast(h) << "}";
    }
    };
    

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59. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 59/128
    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<<(std::ostream& os, my_handle const& h)
    {
    return os << "H{" << ts::get(h) << "}";
    }
    };
    

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60. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 60/128
    Jonathan Boccara @joboccara
    NamedType Implementation of
    strong types in C++
    https://github.com/joboccara/NamedType
    

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61. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 61/128
    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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62. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 62/128
    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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63. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 63/128
    #include
    using my_handle =
    fluent::NamedType<
    int, struct my_handle_tag
    >;
    https://github.com/joboccara/NamedType
    

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64. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 64/128
    #include
    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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65. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 65/128
    #include
    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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66. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 66/128
    #include
    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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67. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 67/128
    ●
    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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68. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 68/128
    Network capacity utilisation
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    A slot is a network capacity quanta
    

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69. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 69/128
    Network capacity utilisation
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    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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70. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 70/128
    Network capacity utilisation
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    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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71. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 71/128
    Magic Numbers
    

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72. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 72/128
    SlotCount availableCapacity();
    ...
    if (availableCapacity() == 0) {
    ...
    }
    

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73. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 73/128
    SlotCount availableCapacity();
    ...
    if (availableCapacity() == SlotCount{0}) {
    ...
    }
    

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74. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 74/128
    SlotCount availableCapacity();
    constexpr SlotCount noSlots{0};
    ...
    if (availableCapacity() == noSlots) {
    ...
    }
    

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75. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 75/128
    Encapsulation
    

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76. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 76/128
    class MessageBuffer
    {
    public:
    template
    void serialize_bits(unsigned value);
    };
    SlotCount capacity = ...
    MessageBuffer buffer ...
    buffer.serialize_bits<24>(capacity);
    

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77. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 77/128
    class MessageBuffer
    {
    public:
    template
    void serialize_bits(unsigned value);
    };
    SlotCount capacity = ...
    MessageBuffer buffer ...
    buffer.serialize_bits<24>(capacity);
    

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78. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 78/128
    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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79. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 79/128
    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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80. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 80/128
    Type Semantics
    

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81. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 81/128
    class SlotPool {
    public:
    void releaseCapacity(std::vector const& ranges)
    SlotCount availableCapacity() const { return unusedSlots;}
    ...
    private:
    SlotCount unusedSlots;
    ...
    };
    

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82. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 82/128
    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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83. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 83/128
    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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84. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 84/128
    Which operations makes sense?
    SlotCount+SlotCount?
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

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85. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 85/128
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

86. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 86/128
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    SlotCount-SlotCount?
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

87. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 87/128
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    SlotCount-SlotCount->SlotCount
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

88. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 88/128
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    SlotCount-SlotCount->SlotCount
    SlotCount*SlotCount?
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

89. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 89/128
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    SlotCount-SlotCount->SlotCount
    SlotCount*SlotCount
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

90. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 90/128
    Which operations makes sense?
    SlotCount+SlotCount->SlotCount
    SlotCount-SlotCount->SlotCount
    SlotCount*SlotCount
    SlotCount*Ratio?
    0 1 2 3 4 5 6 7 8 9 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

91. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 91/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

92. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 92/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

93. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 93/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

94. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 94/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

95. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 95/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

96. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 96/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

97. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 97/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

98. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 98/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

99. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 99/128
    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 10 11 121314151617181920212223
    Frame with 24 slots
    

    View Slide

100. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 100/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

101. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 101/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

102. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 102/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

103. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 103/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

104. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 104/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

105. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 105/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

106. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 106/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

107. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 107/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

108. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 108/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

109. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 109/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

110. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 110/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

111. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 111/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

     View Slide

112. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 112/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

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113. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 113/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     

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114. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 114/128
     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 10 11 121314151617181920212223
     Frame with 24 slots
     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
     

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115. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 115/128
     Test Code
     

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116. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 116/128
     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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117. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 117/128
     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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118. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 118/128
     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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119. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 119/128
     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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120. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 120/128
     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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121. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 121/128
     ●
     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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122. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 122/128
     ●
     Safety for built in types is abysmal in C++
     Type Safe C++? - LOL! :-)
     

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123. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 123/128
     ●
     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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124. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 124/128
     ●
     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! :-)
     

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125. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 125/128
     ●
     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! :-)
     

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126. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 126/128
     ●
     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! :-)
     

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127. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 127/128
     ●
     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
     

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128. Type Safe C++? - LOL! :-) – NDC{Oslo} 2018 – © Björn Fahller @bjorn_fahller 128/128
     Björn Fahller
     bjorn@fahller.se
     @bjorn_fahller
     @rollbear cpplang, swedencpp
     Type Safe C++? - LOL! :-)
     https://github.com/rollbear/strong_type
     

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