NAME¶

deductionguidesforstd::function - deductionguidesforstd::function

Synopsis¶

Defined in header <functional>
template< class R, class... ArgTypes > (1) (since C++17)
function( R(*)(ArgTypes...) ) -> function<R(ArgTypes...)>;
template< class F > (2) (since C++17)
function( F ) -> function</*see below*/>;

1) This deduction guide is provided for std::function to allow deduction from
functions.
2) This overload participates in overload resolution only if &F::operator() is
well-formed when treated as an unevaluated operand and decltype(&F::operator()) is
of the form R(G::*)(A...) (optionally cv-qualified, optionally noexcept, optionally
lvalue reference qualified) for some class type G. The deduced type is
std::function<R(A...)>.

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¶

// Run this code

#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)>
}

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3238 C++17 behavior of (2) was unclear clarified