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deduction guides for std::function

Defined in header <functional>
template<class R, class... ArgTypes> 
function(R(*)(ArgTypes...)) -> function<R(ArgTypes...)>;
(1) (since C++17)
template<class F>
function(F) -> function</*see below*/>;
(2) (since C++17)
1) This deduction guide is provided for std::function to allow deduction from functions.
2) If decltype(&F::operator()) is of the form R(G::*)(A...) (optionally cv-qualified, optionally noexcept, optionally lvalue reference qualified) for some class type G, then the deduced type is std::function<R(A...)>. This overload only participates in overload resolution if &F::operator() is well-formed when treated as an unevaluated operand.

Notes

The type deduced by these deduction guides may change in a later standard revision (in particular, this might happen if noexcept support is added to std::function in a later standard).

Example

#include <functional>
int func(double) { return 0; }
int main() {
  std::function f{func}; // guide #1 deduces function<int(double)>
  int i = 5;
  std::function g = [&](double) { return i; }; // guide #2 deduces function<int(double)>
}

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