NAME¶

std::is_bind_expression - std::is_bind_expression

Synopsis¶

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

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 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.

Member constants¶

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

Member functions¶

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

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 can be derived from
only be derived from std::false_type std::true_type

See also¶

bind binds one or more arguments to a function object
(C++11) (function template)