|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Defined in header <tuple> | ||
template<class F,class Tuple> constexpr decltype(auto) apply( F&& f, Tuple&& t); | (since C++17) (until C++23) | |
template<class F, tuple-like Tuple> constexpr decltype(auto) apply( F&& f, Tuple&& t)noexcept(/* see below */); | (since C++23) | |
Invoke theCallable objectf with the elements oft as arguments.
Given the exposition-only functionapply-impl defined as follows:
template<class F,class Tuple,std::size_t...I>
constexpr decltype(auto) apply-impl(F&& f, Tuple&& t,std::index_sequence<I...>)// exposition only{ return INVOKE(std::forward<F>(f), std::get<I>(std::forward<Tuple>(t))...);}
The effect is equivalent to:
return apply-impl(std::forward<F>(f),std::forward<Tuple>(t), std::make_index_sequence< std::tuple_size_v<std::decay_t<Tuple>>>{});.
Contents |
| f | - | Callable object to be invoked |
| t | - | tuple whose elements to be used as arguments tof |
The value returned byf.
(none) | (until C++23) |
noexcept specification: noexcept( noexcept(std::invoke(std::forward<F>(f), where
| (since C++23) |
| (until C++23) |
| (since C++23) |
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_apply | 201603L | (C++17) | std::apply |
#include <iostream>#include <tuple>#include <utility> int add(int first,int second){return first+ second;} template<typename T>T add_generic(T first, T second){return first+ second;} auto add_lambda=[](auto first,auto second){return first+ second;}; template<typename...Ts>std::ostream& operator<<(std::ostream& os,std::tuple<Ts...>const& theTuple){ std::apply([&os](Tsconst&...tupleArgs){ os<<'[';std::size_t n{0};((os<< tupleArgs<<(++n!= sizeof...(Ts)?", ":"")), ...); os<<']';}, theTuple);return os;} int main(){// OKstd::cout<< std::apply(add,std::pair(1,2))<<'\n'; // Error: can't deduce the function type// std::cout << std::apply(add_generic, std::make_pair(2.0f, 3.0f)) << '\n'; // OKstd::cout<< std::apply(add_lambda,std::pair(2.0f,3.0f))<<'\n'; // advanced examplestd::tuple myTuple{25,"Hello",9.31f,'c'};std::cout<< myTuple<<'\n';}
Output:
35[25, Hello, 9.31, c]
(C++11) | creates atuple object of the type defined by the argument types(function template)[edit] |
(C++11) | creates atuple offorwarding references(function template)[edit] |
(C++17) | construct an object with a tuple of arguments (function template)[edit] |
(C++17)(C++23) | invokes anyCallable object with given argumentsand possibility to specify return type(since C++23) (function template)[edit] |
