deductionguidesforstdfunction(3)

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) 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

// 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)>
  }