std::is_bind_expression

 

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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*)

 

Defined in header <functional>
template<class T > struct is_bind_expression;		(since C++11)

If T is a type produced by a call to std::bind (but not std::bind_front or std::bind_back), this template is derived from std::true_type. For any other type (unless user-specialized), this template is derived from std::false_type.

A program may specialize this template for a program-defined typeT to implement UnaryTypeTrait with base characteristic of std::true_type to indicate that T should be treated by std::bind as if it were the type of a bind subexpression: when a bind-generated function object is invoked, a bound argument of this type will be invoked as a function object and will be given all the unbound arguments passed to the bind-generated object.

Helper variable template

template<class T > constexprbool is_bind_expression_v = is_bind_expression<T>::value;		(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

true if T is a function object generated by std::bind, false otherwise (public static member constant)

Member functions

operator bool	converts the object to bool, returns value (public member function)
operator() (C++14)	returns value (public member function)

Member types

Type	Definition
value_type	bool
type	std::integral_constant<bool, value>

Example

Run this code

#include <functional>#include <iostream>#include <type_traits>   struct MyBind {typedefint result_type;int operator()(int a, int b)const{return a + b;}};   namespace std {template<>struct is_bind_expression<MyBind>:public true_type {};}   int f(int n1, int n2){return n1 + n2;}   int main(){// as if bind(f, bind(MyBind(), _1, _2), 2)auto b =std::bind(f, MyBind(), 2);   std::cout<<"Adding 2 to the sum of 10 and 11 gives "<< b(10, 11)<<'\n';}

Output:

Adding 2 to the sum of 10 and 11 gives 23

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 2010	C++11	program-defined specializations could only be derived from std::false_type	can be derived from std::true_type

See also

bind (C++11)

binds one or more arguments to a function object (function template)