std::is_nothrow_move_assignable in C++

The std::is_nothrow_move_assignable template of C++ STL is present in the <type_traits> header file. The std::is_nothrow_move_assignable template of C++ STL is used to check whether the T is a move assignable type or not and this is known for not to throw any exception. It return the boolean value true if T is move assignable type, otherwise return false.

Header File:

#include<type_traits>

Template Class:

template< class T >
struct is_move_assignable;

Syntax:

std::is_move_assignable<T>::value 

Parameter: The template std::is_nothrow_move_assignable accepts a single parameter T(Trait class) to check whether T is move assignable with no throw exception or not.

Return Value: The template std::is_nothrow_move_assignable returns a boolean variable as shown below:

• True: If the type T is move assignable type.
• False: If the type T is not a move assignable type.

Below is the program to demonstrate std::is_nothrow_move_assignable:

Program:

// C++ program to illustrate
// std::is_nothrow_move_assignable
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

// Declare structures
struct A {
};

struct B {
    B& operator=(B&) = delete;
};

struct Ex1 {
    Ex1() {}
    Ex1(Ex1&&)
    {
        cout << "Throwing move constructor!";
    }
    Ex1(const Ex1&)
    {
        cout << "Throwing copy constructor!";
    }
};

struct Ex2 {
    Ex2() {}
    Ex2(Ex2&&) noexcept
    {
        cout << "Non-throwing move constructor!";
    }
    Ex2(const Ex2&) noexcept
    {
        cout << "Non-throwing copy constructor!";
    }
};

// Driver Code
int main()
{
    cout << boolalpha;

    // Check if int is a move
    // assignable or not
    cout << "int: "
         << is_nothrow_move_assignable<int>::value
         << endl;

    // Check if struct A is a move
    // assignable or not
    cout << "struct A: "
         << is_nothrow_move_assignable<A>::value
         << endl;

    // Check if struct B is a move
    // assignable or not
    cout << "struct B: "
         << is_nothrow_move_assignable<B>::value
         << endl;

    // Check if struct Ex1 is a move
    // assignable or not
    cout << "struct Ex1: "
         << is_nothrow_move_assignable<Ex1>::value
         << endl;

    // Check if struct Ex2 is a move
    // assignable or not
    cout << "struct Ex2: "
         << is_nothrow_move_assignable<Ex2>::value
         << endl;
    return 0;
}

Output:

int: true
struct A: true
struct B: false
struct Ex1: false
struct Ex2: false

Reference: http://www.cplusplus.com/reference/type_traits/is_nothrow_move_assignable/