Code::Dive - Modern Techniques for Keeping Your Code DRY

We have learned to avoid repeating ourselves in code, and yet we keep writing things like:

if (a > 0 && b > 0 && c > 0) ...

In this session, Björn will show techniques from modern C++ that help you construct abstractions for those micro repetitions. These will allow you to write:

if (all_of(a, b, c) > 0) ...

Code like this expresses intent more clearly and therefore makes it easier to follow the logic of the intended functionality instead of focussing on code details. This makes it easier to understand the functionality, and also makes it easier to spot mistakes. Better yet, these abstractions carry no run time cost.

After this session, you will be able to write your own zero-cost abstractions that help getting rid of the patterns that keep repeating in your code.

Transcript

1. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 1/127 Modern Techniques for Keeping Your Code DRY <C++> Björn Fahller
2. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 2/127 assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
3. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 3/127 assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
4. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 4/127 Modern Techniques for Keeping Your Code DRY <C++> Björn Fahller
5. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 5/127 Modern Techniques for Keeping Your Code DRY <C++> Björn Fahller
6. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 6/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
7. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 7/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); variadic function template
8. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 8/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> bool is_any_of(state_type s, const Ts& ==. ts) { return ((s == ts) =| ==.); } assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
9. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 9/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> bool is_any_of(state_type s, const Ts& ==. ts) { return ((s == ts) =| ==.); } assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
10. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 10/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> bool is_any_of(state_type s, const Ts& ==. ts) { return ((s == ts) =| ==.); } assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
11. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 11/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> bool is_any_of(state_type s, const Ts& ==. ts) { return ((s == ts) =| ==.); } assert(is_any_of(state, IDLE, DISCONNECTING, DISCONNECTED));
12. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 12/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> bool is_any_of(state_type s, const Ts& ==. ts) { return ((s == ts) =| ==.); } assert(is_any_of(state, IDLE, DISCONNECTING, DISCONNECTED)); Utterly unreadable trash code!
13. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 13/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); variadic non-type template parameter function template
14. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 14/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <state_type ==. states> bool is_any_of(state_type t) { return ((t == states) =| ==.); } assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
15. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 15/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <state_type ==. states> bool is_any_of(state_type t) { return ((t == states) =| ==.); } assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
16. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 16/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <state_type ==. states> bool is_any_of(state_type t) { return ((t == states) =| ==.); } assert(is_any_of<IDLE, DISCONNECTING, DISCONNECTED>(state));
17. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 17/127 auto for non-type template parameters from C++17 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <auto ==. alternatives, typename T> bool is_any_of(const T& t) { return ((t == alternatives) =| ==.); } assert(is_any_of<IDLE, DISCONNECTING, DISCONNECTED>(state));
18. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 18/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <auto ==. alternatives, typename T> bool is_any_of(const T& t) { return ((t == alternatives) =| ==.); } assert(is_any_of<IDLE, DISCONNECTING, DISCONNECTED>(state)); Not all types can be used as non-type template parameters Only constexpr values Yoda speak
19. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 19/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); construct then test
20. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 20/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
21. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 21/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> auto is_in(const T& t) { return [t](const auto& ==. vs) { return ((t == vs) =| ==.); }; } assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
22. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 22/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> auto is_in(const T& t) { return [t](const auto& ==. vs) { return ((t == vs) =| ==.); }; } assert(is_in(state)(IDLE, DISCONNECTING, DISCONNECTED));
23. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 23/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> auto is_in(const T& t) { return [t](const auto& ==. vs) { return ((t == vs) =| ==.); }; } assert(is_in(state)(IDLE, DISCONNECTING, DISCONNECTED));
24. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 24/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> auto is_in(const T& t) { return [t](const auto& ==. vs) { return ((t == vs) =| ==.); }; } assert(is_in(state)(IDLE, DISCONNECTING, DISCONNECTED)); Works with all types Looks horrible Is a bit too terse
25. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 25/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); explicit construct and compare function
26. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 26/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> struct is { T t; template <typename ==. Ts> bool any_of(const Ts& ==. ts) const { return ((t == ts) =| ==.); } }; template <typename T> is(T) => is<T>; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
27. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 27/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> struct is { T t; template <typename ==. Ts> bool any_of(const Ts& ==. ts) const { return ((t == ts) =| ==.); } }; template <typename T> is(T) => is<T>; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
28. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 28/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> struct is { T t; template <typename ==. Ts> bool any_of(const Ts& ==. ts) const { return ((t == ts) =| ==.); } }; template <typename T> is(T) => is<T>; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); C++17 Deduction Guide for Constructor Template Argument Deduction
29. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 29/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> struct is { T t; template <typename ==. Ts> bool any_of(const Ts& ==. ts) const { return ((t == ts) =| ==.); } }; template <typename T> is(T) => is<T>; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); C++17 Deduction Guide for Constructor Template Argument Deduction https://youtu.be/-H-ut6j1BYU https://youtu.be/UDs90b0yjjQ
30. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 30/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename T> struct is { T t; template <typename ==. Ts> bool any_of(const Ts& ==. ts) const { return ((t == ts) =| ==.); } }; template <typename T> is(T) => is<T>; assert(is{state}.any_of(IDLE, DISCONNECTING, DISCONNECTED)); Works with all types Explicit Still Yoda speak
31. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 31/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); time passes...
32. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 32/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); your mildly annoyed developer stays annoyed...
33. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 33/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED); Then one day, two years later!
34. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 34/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE =| state == DISCONNECTING =| state == DISCONNECTED);
35. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 35/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&… ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(any_of(IDLE, DISCONNECTING, DISCONNECTED) == state);
36. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 36/127 Pure laziness, but these give me 18 constructors enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(any_of(IDLE, DISCONNECTING, DISCONNECTED) == state);
37. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 37/127 Call function with each member of the tuple as a parameter. enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(state == any_of(IDLE, DISCONNECTING, DISCONNECTED));
38. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 38/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> friend bool operator==(const T& lh, const any_of& rh) { return rh == lh;} }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(state == any_of(IDLE, DISCONNECTING, DISCONNECTED)); Provide symmetric operator==
39. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 39/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> friend bool operator==(const T& lh, const any_of& rh) { return rh == lh;} }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(state == any_of(IDLE, DISCONNECTING, DISCONNECTED)); Maybe exaggerated cuteness, but I like this!
40. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 40/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> friend bool operator==(const T& lh, const any_of& rh) { return rh == lh;} }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(state == any_of(IDLE, DISCONNECTING, DISCONNECTED)); https://gcc.godbolt.org/z/IY865r
41. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 41/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> friend bool operator==(const T& lh, const any_of& rh) { return rh == lh;} }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(state == any_of(IDLE, DISCONNECTING, DISCONNECTED));
42. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 42/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> friend bool operator==(const T& lh, const any_of& rh) { return rh == lh;} }; template <typename ==. Ts> any_of(Ts==.) => any_of<Ts==.>; assert(state == any_of(IDLE, DISCONNECTING, DISCONNECTED)); Add relational operators!
43. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 43/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> bool operator<(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts < t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } ==. }; while (any_of(a, b, c) < 0) ==.
44. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 44/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> bool operator<(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts < t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } ==. }; while (any_of(a, b, c) < 0) ==.
45. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 45/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> bool operator<(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts < t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } ==. }; while (any_of(a, b, c) < 0) ==. https://gcc.godbolt.org/z/YyvAtT
46. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 46/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> bool operator<(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts < t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } ==. }; while (any_of(a, b, c) < 0) ==.
47. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 47/127 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts == t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } template <typename T> bool operator<(const T& t) const { return std=:apply([&t](const auto&==. ts){ return ((ts < t) =| ==.);}, static_cast<const std=:tuple<Ts==.>&>(*this)); } ==. }; while (any_of(a, b, c) < 0) ==. An awful lot of repetition here!
48. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 48/127 template <typename F, typename ==. Ts> bool or_elements(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&f](const auto& ==. ts){ return (f(ts) =| ==.);}, t); }
49. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 49/127 template <typename F, typename ==. Ts> bool or_elements(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&f](const auto& ==. ts){ return (f(ts) =| ==.);}, t); }
50. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 50/127 template <typename F, typename ==. Ts> bool or_elements(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&f](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return or_elements([&t](const auto& v){ return v == t;}, *this); } template <typename T> bool operator<(const T& t) const { return or_elements([&t](const auto& v){ return v < t;}, *this); } }; while (any_of(a, b, c) < 0) ==.
51. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 51/127 template <typename F, typename ==. Ts> bool or_elements(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&f](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return or_elements([&t](const auto& v){ return v == t;}, *this); } template <typename T> bool operator<(const T& t) const { return or_elements([&t](const auto& v){ return v < t;}, *this); } }; while (any_of(a, b, c) < 0) ==. https://godbolt.org/z/SP8POJ
52. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 52/127 template <typename F, typename ==. Ts> bool or_elements(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&f](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } template <typename ==. Ts> struct any_of : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return or_elements([&t](const auto& v){ return v == t;}, *this); } template <typename T> bool operator<(const T& t) const { return or_elements([&t](const auto& v){ return v < t;}, *this); } }; while (any_of(a, b, c) < 0) ==. each_of? Repeat Everything Again?
53. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 53/127 struct or_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct any_of : op_t<or_elements, Ts==.> { using op_t<or_elements, Ts==.>=:op_t; };
54. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 54/127 struct or_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct any_of : op_t<or_elements, Ts==.> { using op_t<or_elements, Ts==.>=:op_t; };
55. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 55/127 struct or_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct any_of : op_t<or_elements, Ts==.> { using op_t<or_elements, Ts==.>=:op_t; };
56. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 56/127 struct or_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =| ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct any_of : op_t<or_elements, Ts==.> { using op_t<or_elements, Ts==.>=:op_t; };
57. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 57/127 struct and_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =& ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct each_of : op_t<and_elements, Ts==.> { using op_t<and_elements, Ts==.>=:op_t; };
58. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 58/127 struct and_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =& ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct each_of : op_t<and_elements, Ts==.> { using op_t<and_elements, Ts==.>=:op_t; }; template <typename ==. Ts> using each_of = op_t<and_elements, Ts==.>; In a better world we could deduce constructor template args for aliases too
59. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 59/127 struct and_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =& ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct each_of : op_t<and_elements, Ts==.> { using op_t<and_elements, Ts==.>=:op_t; }; template <typename ==. Ts> using each_of = op_t<and_elements, Ts==.>; In a better world we could deduce constructor template args for aliases too You can from C++20
60. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 60/127 struct and_elements { template <typename F, typename ==. Ts> static bool apply(const F& f, const std=:tuple<Ts==.>& t) { return std=:apply([&](const auto& ==. ts){ return (f(ts) =& ==.);}, t); } }; template <typename Op, typename ==. Ts> struct op_t : private std=:tuple<Ts==.> { using std=:tuple<Ts==.>=:tuple; template <typename T> bool operator==(const T& t) const { return Op=:apply([&t](const auto& v){ return v == t;}, *this); } ==. }; template <typename ==. Ts> struct each_of : op_t<and_elements, Ts==.> { using op_t<and_elements, Ts==.>=:op_t; }; https://gcc.godbolt.org/z/Ay1TA_
61. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 61/127 Can we try something else?
62. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 62/127 Can we try something else? I think lambdas are cool!
63. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 63/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; assert(tuple(a,b,c)([](auto ==. e){ return ((e > 0) =& ==.); }));
64. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 64/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; assert(tuple(a,b,c)([](auto ==. e){ return ((e > 0) =& ==.); }));
65. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 65/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; assert(tuple(a,b,c)([](auto ==. e){ return ((e > 0) =& ==.); }));
66. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 66/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto ==. elements) { return (func(elements) =& ==.); }; }; assert(tuple(a,b,c)(and_elements([](auto e){ return e > 0;}));
67. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 67/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto ==. elements) { return (func(elements) =& ==.); }; }; assert(tuple(a,b,c)(and_elements([](auto e){ return e > 0;}));
68. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 68/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto ==. elements) { return (func(elements) =& ==.); }; }; assert(tuple(a,b,c)(and_elements([](auto e){ return e > 0;}));
69. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 69/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto ==. elements) { return (func(elements) =& ==.); }; }; constexpr auto bind_rh = [](auto func, auto rh) { return [=](auto lh) { return func(lh, rh); }; }; assert(tuple(a,b,c)(and_elements([](auto e){ return e > 0;}));
70. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 70/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto … elements) { return (func(elements) =& ==.); }; }; constexpr auto bind_rh = [](auto func, auto rh) { return [=](auto lh) { return func(lh, rh); }; }; constexpr auto greater_than = [](auto rh) { return bind_rh(std=:greater{}, rh); }; assert(tuple(a,b,c)(and_elements([](auto e){ return e > 0;}));
71. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 71/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto … elements) { return (func(elements) =& ==.); }; }; constexpr auto bind_rh = [](auto func, auto rh) { return [=](auto lh) { return func(lh, rh); }; }; constexpr auto greater_than = [](auto rh) { return bind_rh(std=:greater{}, rh); }; assert(tuple(a,b,c)(and_elements(greater_than(0)));
72. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 72/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = [](auto func) { return [=](auto … elements) { return (func(elements) =& ==.); }; }; constexpr auto bind_rh = [](auto func, auto rh) { return [=](auto lh) { return func(lh, rh); }; }; constexpr auto greater_than = [](auto rh) { return bind_rh(std=:greater{}, rh); }; assert(tuple(a,b,c)(and_elements(greater_than(0)));
73. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 73/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0);
74. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 74/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0);
75. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 75/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0);
76. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 76/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0);
77. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 77/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0);
78. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 78/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); C++20 attribute to make empty member take no space. If saving this byte is important pre C++20, use private inheritance for Empty Base Class Optimization.
79. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 79/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0);
80. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 80/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); https://gcc.godbolt.org/z/uyDzC8
81. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 81/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve:
82. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 82/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> auto apply(F f) const{ return tup(func(f)); } public: op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> auto operator>(const T& t) const{ return apply(greater_than(t)); } }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve: • constexpr
83. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 83/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F f) const{ return tup(func(f)); } public: constexpr op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve: • constexpr
84. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 84/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F f) const{ return tup(func(f)); } public: constexpr op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve: ✔ constexpr • Perfect forwarding
85. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 85/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F f) const{ return tup(func(f)); } public: constexpr op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve: ✔ constexpr • Perfect forwarding • Conditional noexcept
86. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 86/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F f) const{ return tup(func(f)); } public: constexpr op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve: ✔ constexpr • Perfect forwarding • Conditional noexcept • Explicit return type
87. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 87/127 constexpr auto tuple = [](auto ==. ts) ==. constexpr auto and_elements = [](auto func) ==. constexpr auto equal_to = [](auto rh) ==. constexpr auto greater_than = [](auto rh) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F f) const{ return tup(func(f)); } public: constexpr op_t(Func f, Tuple t) : tup(t), func(f) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[](auto==.ts){ return op_t(and_elements,tuple(ts==.));}; assert(each_of(a,b,c) > 0); Things to improve: ✔ constexpr • Perfect forwarding • Conditional noexcept • Explicit return type
88. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 88/127 constexpr auto and_elements = [](auto func) { return [=](auto ==. elements) { return (func(elements) =& ==.); }; };
89. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 89/127 constexpr auto and_elements = [](auto=& func) { return [func = std=:forward<decltype(func)>(func)](auto ==. elements) { return (func(elements) =& ==.); }; };
90. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 90/127 constexpr auto and_elements = [](auto=& func) { return [func = std=:forward<decltype(func)>(func)](auto ==. elements) { return (func(elements) =& ==.); }; };
91. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 91/127 constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) { return (func(elements) =& ==.); }; }; C++20 allows us to explicitly state template parameters to lambdas.
92. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 92/127 constexpr auto tuple = [](auto ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) { return (func(elements) =& ==.); }; };
93. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 93/127 constexpr auto tuple = [](auto=& ==. ts) { return [=](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) { return (func(elements) =& ==.); }; }; Not possible to forward parameter packs in C++14 or C++17!
94. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 94/127 constexpr auto tuple = [](auto=& ==. ts) { return [==.ts = std=:forward<decltype(ts)>(ts)](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) { return (func(elements) =& ==.); }; }; C++20 parameter pack capture with perfect forwarding.
95. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 95/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) { return (func(elements) =& ==.); }; };
96. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 96/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : Func(std=:move(f)), tup(std=:move(t)) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[]<typename ==. Ts>(Ts=&==. ts){ return op_t(and_elements,tuple(std=:forward<Ts>(ts)==.)); };
97. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 97/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : Func(std=:move(f)), tup(std=:move(t)) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[]<typename ==. Ts>(Ts=&==. ts){ return op_t(and_elements,tuple(std=:forward<Ts>(ts)==.)); }; Things to improve: ✔ constexpr ✔ Perfect forwarding • Conditional noexcept • Explicit return type
98. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 98/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : Func(std=:move(f)), tup(std=:move(t)) {} template <typename T> constexpr auto operator==(const T& t) const { return apply(equal_to(t)); } template <typename T> constexpr auto operator>(const T& t) const{ return apply(greater_than(t));} }; constexpr auto each_of=[]<typename ==. Ts>(Ts=&==. ts){ return op_t(and_elements,tuple(std=:forward<Ts>(ts)==.)); }; Things to improve: ✔ constexpr ✔ Perfect forwarding • Conditional noexcept • Explicit return type
99. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 99/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto … elements) { return (func(elements) =& ==.); }; };
100. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 100/127 7,82 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) noexcept(noexcept(func(ts==.))) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) noexcept(noexcept((func(elements) =& ==.))) { return (func(elements) =& ==.); }; }; Yes, double parenthesis
101. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 101/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) noexcept(noexcept(func(ts==.))) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) noexcept(noexcept((func(elements) =& ==.))) { return (func(elements) =& ==.); }; }; There’s no way around this repetition!
102. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 102/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const noexcept(noexcept(tup(func(std=:forward<F>(f))))) { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : tup(std=:move(t)), func(std=:move(f)) {} template <typename T> constexpr auto operator==(const T& t) const noexcept(noexcept(apply(equal_to(t)))) { return apply(equal_to(t)); } ==. };
103. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 103/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const noexcept(noexcept(tup(func(std=:forward<F>(f))))) { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : tup(std=:move(t)), func(std=:move(f)) {} template <typename T> constexpr auto operator==(const T& t) const noexcept(noexcept(apply(equal_to(t)))) { return apply(equal_to(t)); } ==. };
104. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 104/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const noexcept(noexcept(tup(func(std=:forward<F>(f))))) { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : tup(std=:move(t)), func(std=:move(f)) {} template <typename T> constexpr auto operator==(const T& t) const noexcept(noexcept(apply(equal_to(t)))) { return apply(equal_to(t)); } ==. }; Ugly ugly repetition!
105. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 105/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const noexcept(noexcept(tup(func(std=:forward<F>(f))))) { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : tup(std=:move(t)), func(std=:move(f)) {} template <typename T> constexpr auto operator==(const T& t) const noexcept(noexcept(apply(equal_to(t)))) { return apply(equal_to(t)); } ==. }; Things to improve: ✔ constexpr ✔ Perfect forwarding ✔ Conditional noexcept • Explicit return type
106. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 106/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const noexcept(noexcept(tup(func(std=:forward<F>(f))))) { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : tup(std=:move(t)), func(std=:move(f)) {} template <typename T> constexpr auto operator==(const T& t) const noexcept(noexcept(apply(equal_to(t)))) { return apply(equal_to(t)); } ==. }; Things to improve: ✔ constexpr ✔ Perfect forwarding ✔ Conditional noexcept • Explicit return type
107. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 107/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) noexcept(noexcept(func(ts…))) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) noexcept(noexcept((func(elements) =& ==.))) { return (func(elements) =& ==.); }; };
108. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 108/127 Yes, double parenthesis constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) noexcept(noexcept(func(ts==.))) => decltype(func(ts==.)) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) noexcept(noexcept((func(elements) =& ==.))) => decltype((func(elements) =& ==.)) { return (func(elements) =& ==.); }; }; 7,82
109. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 109/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) noexcept(noexcept(func(ts==.))) => decltype(func(ts==.)) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) noexcept(noexcept((func(elements) =& ==.))) => decltype((func(elements) =& ==.)) { return (func(elements) =& ==.); }; }; "Ellie, Colorkey, cateye" by Isaril is licensed under CC BY-NC-SA 2.0 https://flic.kr/p/Jp53FM
110. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 110/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) { return [==.ts = std=:forward<Ts>(ts)](const auto& func) noexcept(noexcept(func(ts==.))) => decltype(func(ts==.)) { return func(ts==.); }; }; constexpr auto and_elements = []<typename T>(T=& func) { return [func = std=:forward<T>(func)](auto ==. elements) noexcept(noexcept((func(elements) =& ==.))) => decltype((func(elements) =& ==.)) { return (func(elements) =& ==.); }; }; www.youtube.com/watch?v=I3T4lePH-yA
111. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 111/127 constexpr auto tuple = []<typename ==. Ts>(Ts=& ==. ts) ==. constexpr auto and_elements = []<typename T>(T=& func) ==. template <typename Func, typename Tuple> class op_t { Tuple tup; [[no_unique_address]] Func func; template <typename F> constexpr auto apply(F=& f) const noexcept(noexcept(tup(func(std=:forward<F>(f))))) => decltype(tup(func(std=:forward<F>(f)))) { return tup(func(std=:forward<F>(f))); } public: constexpr op_t(Func f, Tuple t) : tup(std=:move(t)), func(std=:move(f)) {} template <typename T> constexpr auto operator==(const T& t) const noexcept(noexcept(apply(equal_to(t)))) => decltype(apply(equal_to(t))) { return apply(equal_to(t)); } Things to improve: ✔ constexpr ✔ Perfect forwarding ✔ Conditional noexcept ✔ Explicit return type
112. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 112/127 That was
113. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 113/127 Modern Techniques for Keeping Your Code DRY That was
114. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 114/127 Björn Fahller Modern Techniques for Keeping Your Code DRY That was
115. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 115/127 Björn Fahller Modern Techniques for Keeping Your Code DRY That was Remember
116. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 116/127 Björn Fahller Modern Techniques for Keeping Your Code DRY That was Remember • Fold expressions are awesome
117. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 117/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome
118. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 118/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome
119. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 119/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome
120. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 120/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer!
121. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 121/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer! • Compilers are awesome
122. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 122/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer! • Compilers are awesome Matt Godbolt is awesome!
123. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 123/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer! • Compilers are awesome • noexcept/SFINAE-return is aweso^H^Hful
124. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 124/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer! • Compilers are awesome • noexcept/SFINAE-return is aweso^H^Hful • Sweating the small stuff makes you annoyed
125. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 125/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer! • Compilers are awesome • noexcept/SFINAE-return is aweso^H^Hful • Sweating the small stuff makes you annoyed • But it can lead to neat code
126. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 126/127 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome • Higher order functions are awesome • Lambdas are awesome • C++20 lambdas are awsomer! • Compilers are awesome • noexcept/SFINAE-return is aweso^H^Hful • Sweating the small stuff makes you annoyed • But it can lead to neat code <C++>
127. Modern DRY C++ –– code::dive 2019 © Björn Fahller @bjorn_fahller 127/127 bjorn@fahller.se @bjorn_fahller @rollbear Björn Fahller Modern Techniques for Keeping Your Code DRY