deduction guides for std::packaged_task

Since C++17

Header: <future>

  1. This deduction guide is provided for std::packaged_task to allow deduction from functions.

# Declarations

template< class R, class... Args >
packaged_task( R(*)(Args...) ) -> packaged_task<R(Args...)>;

(since C++17)

template< class F >
packaged_task( F ) -> packaged_task</*see below*/>;

(since C++17)

template< class F >
packaged_task( F ) -> packaged_task</*see below*/>;

(since C++23)

template< class F >
packaged_task( F ) -> packaged_task</*see below*/>;

(since C++23)

# Notes

These deduction guides do not allow deduction from a function with ellipsis parameter, and the … in the types is always treated as a pack expansion.

# Example

#include <future>
 
int func(double) { return 0; }
 
int main()
{
    std::packaged_task f{func}; // deduces packaged_task<int(double)>
 
    int i = 5;
    std::packaged_task g = [&](double) { return i; }; // => packaged_task<int(double)>
}