std::is_bind_expression

< cpp‎ | utility‎ | functional

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

If T is the type produced by a call to std::bind, this template is derived from std::true_type. For any other type, this template is derived from std::false_type.

This template may be specialized for a user-defined type T 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 > inline constexpr bool 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

#include <iostream>
#include <type_traits>
#include <functional>
 
struct MyBind {
    typedef int 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