deductiongu...ckaged_task(3) C++ Standard Libary deductiongu...ckaged_task(3) NAME deductionguidesforstd::packaged_task - deductionguidesforstd::packaged_task Synopsis Defined in header <future> template< class R, class... Args > (1) (since C++17) packaged_task( R(*)(Args...) ) -> packaged_task<R(Args...)>; template< class F > (2) (since C++17) packaged_task( F ) -> packaged_task</*see below*/>; template< class F > (3) (since C++23) packaged_task( F ) -> packaged_task</*see below*/>; template< class F > (4) (since C++23) packaged_task( F ) -> packaged_task</*see below*/>; 1) This deduction guide is provided for std::packaged_task to allow de- duction from functions. 2) This overload participates in overload resolution only if &F::opera- tor() is well-formed when treated as an unevaluated operand and decltype(&F::op- erator()) is of the form R(G::*)(A...) (optionally cv-qualified, optionally noexcept, optionally lvalue reference qualified). The deduced type is std::pack- aged_task<R(A...)>. 3) This overload participates in overload resolution only if &F::opera- tor() is well-formed when treated as an unevaluated operand and F::operator() is an explicit object parameter function whose type is of form R(G, A...) or R(G, A...) noexcept. The deduced type is std::packaged_task<R(A...)>. 4) This overload participates in overload resolution only if &F::opera- tor() is well-formed when treated as an unevaluated operand and F::operator() is a static member function whose type is of form R(A...) or R(A...) noexcept. The deduced type is std::packaged_task<R(A...)>. Notes These deduction guides do not allow deduction from a function with el- lipsis parameter, and the ... in the types is always treated as a pack expan- sion. Example // Run this code #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; }; // => pack- aged_task<int(double)> } http://cppreference.com 2024.06.10 deductiongu...ckaged_task(3)
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