std::move_only_function::operator()

 

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Function wrappers function (C++11) move_only_function (C++23) copyable_function (C++26) function_ref (C++26) mem_fn (C++11) bad_function_call (C++11)	Partial function application bind_frontbind_back (C++20)(C++23) bind (C++11) is_bind_expression (C++11) is_placeholder (C++11) _1, _2, _3, ... (C++11)
Function invocation invokeinvoke_r (C++17)(C++23) Identity function object identity (C++20)	Reference wrappers reference_wrapper (C++11) refcref (C++11)(C++11) unwrap_referenceunwrap_ref_decay (C++20)(C++20)
Operator wrappers plus minus negate multiplies divides modulus bit_and bit_or bit_not (C++14)   bit_xor equal_to not_equal_to greater less greater_equal less_equal logical_and logical_or logical_not	Transparent operator wrappers plus<> (C++14) minus<> (C++14) negate<> (C++14) multiplies<> (C++14)   divides<> (C++14) modulus<> (C++14) bit_and<> (C++14) bit_or<> (C++14) bit_not<> (C++14) bit_xor<> (C++14) equal_to<> (C++14) not_equal_to<> (C++14) greater<> (C++14) less<> (C++14) greater_equal<> (C++14) less_equal<> (C++14) logical_and<> (C++14) logical_or<> (C++14) logical_not<> (C++14)
Negators not_fn (C++17) Searchers default_searcher (C++17) boyer_moore_searcher (C++17) boyer_moore_horspool_searcher (C++17)	Constrained comparators ranges::equal_to (C++20) ranges::not_equal_to (C++20) ranges::greater (C++20) ranges::less (C++20) ranges::greater_equal (C++20) ranges::less_equal (C++20) compare_three_way (C++20)
Old binders and adaptors
unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

std::move_only_function

Member functions

move_only_function::move_only_function

move_only_function::~move_only_function

move_only_function::operator=

move_only_function::swap

move_only_function::operator bool

move_only_function::operator()

Non-member functions

operator==

swap(std::move_only_function)

 

R operator()( Args... args)/*cv*//*ref*/noexcept(/*noex*/);		(since C++23)

Invokes the stored callable target with the parameters args. The /*cv*/, /*ref*/, and /*noex*/ parts of operator() are identical to those of the template parameter of std::move_only_function.

Equivalent to returnstd::invoke_r<R>(/*cv-ref-cast*/(f), std::forward<Args>(args)...);, where f is a cv-unqualified lvalue that denotes the target object of *this, and /*cv-ref-cast*/(f) is equivalent to:

• f if cvref is either empty or &, or
• std::as_const(f) if cvref is either const or const&, or
• std::move(f) if cvref is &&, or
• std::move(std::as_const(f)) if cvref is const&&.

The behavior is undefined if *this is empty.

Parameters

args

-

parameters to pass to the stored callable target

Return value

std::invoke_r<R>(/*cv-ref-cast*/(f), std::forward<Args>(args)...).

Exceptions

Propagates the exception thrown by the underlying function call.

Example

The following example shows how std::move_only_function can passed to other functions by value. Also, it shows how std::move_only_function can store lambdas.

Run this code

#include <iostream>#include <functional>   void call(std::move_only_function<int()const> f)// can be passed by value{std::cout<< f()<<'\n';}   int normal_function(){return42;}   int main(){int n =1;auto lambda =[&n](){return n;};std::move_only_function<int()const> f = lambda; call(std::move(f));   n =2; call(lambda);   f = normal_function; call(std::move(f));}

Output:

1 2 42

See also

operator()	invokes the target (public member function of std::function<R(Args...)>)
operator()	calls the stored function (public member function of std::reference_wrapper<T>)
invokeinvoke_r (C++17)(C++23)	invokes any Callable object with given arguments and possibility to specify return type(since C++23) (function template)