NDC{TechTown} - 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 I will show techniques from modern C++ that helps 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 helps getting rid of the patterns that keeps repeating in your code.

Transcript

1. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 1/125 Modern Techniques for Keeping Your Code DRY <C++> Björn Fahller
2. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 2/125 assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED);
3. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 3/125 assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED);
4. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 4/125 Modern Techniques for Keeping Your Code DRY <C++> Björn Fahller
5. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 5/125 Modern Techniques for Keeping Your Code DRY Björn Fahller <C++>
6. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 6/125 Modern Techniques for Keeping Your Code DRY <C++> Björn Fahller
7. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 7/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED);
8. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 8/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); variadic function template
9. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 9/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 10/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 11/125 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);
12. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 12/125 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));
13. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 13/125 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!
14. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 14/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); variadic non-type template parameter function template
15. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 15/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 16/125 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);
17. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 17/125 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));
18. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 18/125 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));
19. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 19/125 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
20. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 20/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); construct then test
21. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 21/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED);
22. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 22/125 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);
23. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 23/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 24/125 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));
25. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 25/125 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
26. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 26/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); explicit construct and compare function
27. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 27/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 28/125 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);
29. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 29/125 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
30. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 30/125 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
31. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 31/125 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
32. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 32/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); time passes...
33. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 33/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); your mildly annoyed developer stays annoyed...
34. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 34/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED); Then one day, two years later!
35. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 35/125 enum state_type { IDLE, CONNECTING, CONNECTED, DISCONNECTING, DISCONNECTED }; assert(state == IDLE || state == DISCONNECTING || state == DISCONNECTED);
36. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 36/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 37/125 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);
38. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 38/125 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));
39. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 39/125 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==
40. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 40/125 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!
41. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 41/125 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
42. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 42/125 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));
43. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 43/125 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!
44. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 44/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 45/125 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) ...
46. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 46/125 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
47. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 47/125 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) ...
48. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 48/125 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!
49. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 49/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 50/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 51/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 52/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 53/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 54/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 55/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 56/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 57/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 58/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 59/125 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/EAuUnM
60. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 60/125 Can we try something else?
61. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 61/125 Can we try something else? Lambdas are so cool!
62. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 62/125 constexpr auto tuple = [](auto ... ts) { return [=](const auto& func) { return func(ts...); }; }; assert(tuple(a,b,c)([](auto ... e){ return ((e > 0) && ...); }));
63. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 63/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 64/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 65/125 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;}));
66. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 66/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 67/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 68/125 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;}));
69. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 69/125 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;}));
70. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 70/125 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)));
71. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 71/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 72/125 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);
73. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 73/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 74/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 75/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 76/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 77/125 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.
78. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 78/125 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);
79. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 79/125 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
80. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 80/125 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:
81. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 81/125 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
82. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 82/125 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
83. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 83/125 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
84. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 84/125 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
85. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 85/125 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
86. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 86/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 87/125 constexpr auto and_elements = [](auto func) { return [=](auto ... elements) { return (func(elements) && ...); }; };
88. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 88/125 constexpr auto and_elements = [](auto&& func) { return [func = std::forward<decltype(func)>(func)](auto ... elements) { return (func(elements) && ...); }; };
89. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 89/125 constexpr auto and_elements = [](auto&& func) { return [func = std::forward<decltype(func)>(func)](auto ... elements) { return (func(elements) && ...); }; };
90. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 90/125 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.
91. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 91/125 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) && ...); }; };
92. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 92/125 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!
93. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 93/125 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.
94. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 94/125 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) && ...); }; };
95. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 95/125 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)...)); };
96. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 96/125 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
97. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 97/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 98/125 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) && ...); }; };
99. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 99/125 3.08 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
100. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 100/125 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!
101. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 101/125 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)); } ... };
102. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 102/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 103/125 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!
104. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 104/125 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
105. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 105/125 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++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 106/125 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) && ...); }; };
107. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 107/125 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) && ...); }; }; 3.08
108. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 108/125 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) && ...); }; }; https://sacratomatovillepost.com/2017/10/03/stop-being-silly/
109. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 109/125 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
110. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 110/125 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
111. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 111/125 That was
112. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 112/125 Modern Techniques for Keeping Your Code DRY That was
113. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 113/125 Björn Fahller Modern Techniques for Keeping Your Code DRY That was
114. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 114/125 Björn Fahller Modern Techniques for Keeping Your Code DRY That was Remember
115. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 115/125 Björn Fahller Modern Techniques for Keeping Your Code DRY That was Remember • Fold expressions are awesome
116. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 116/125 Björn Fahller Modern Techniques for Keeping Your Code DRY Remember • Fold expressions are awesome • std::tuple<> and std::apply() is awsome
117. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 117/125 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
118. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 118/125 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
119. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 119/125 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!
120. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 120/125 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
121. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 121/125 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
122. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 122/125 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
123. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 123/125 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
124. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 124/125 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++>
125. Modern DRY C++ – NDC{TechTown} 2019 © Björn Fahller @bjorn_fahller 125/125 bjorn@fahller.se @bjorn_fahller @rollbear Björn Fahller Modern Techniques for Keeping Your Code DRY