std::is_nothrow_assignable in C++ with Examples

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

Header File:

#include<type_traits>

Template Class:

template< class A, class B >
struct is_nothrow_assignable;

Syntax:

std::is_assignable<A, B>::value

Parameters: The template std::is_assignable accepts the following parameters:

• A: It represents the parameter in which parameter B is implicitly assign.
• B: It represents the parameter type assignable to A.

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

• True: If the type A is assignable to type B.
• False: If the type A is not assignable to type B.

Below is the program to demonstrate std::is_nothrow_assignable template in C++:

Program:

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

// Declare structures
struct A {
};

struct B {
    B& operator=(const A&) noexcept
    {
        return *this;
    }
    B& operator=(const B&)
    {
        return *this;
    }
};

// Declare classes
class GfG {
};

class gfg {
};

enum class AB : int { x,
                      y,
                      z };

// Driver Code
int main()
{

    cout << boolalpha;

    // Check if int& is assignable to
    // double or not
    cout << "is int = double? "
         << is_nothrow_assignable<int&,
                                  double>::value
         << endl;

    // Check if struct A is assignable to
    // srtuct A or not
    cout << "is struct A = struct A? "
         << is_nothrow_assignable<A, A>::value
         << endl;

    // Check if struct B is assignable to
    // srtuct A or not
    cout << "is class B = class A? "
         << is_nothrow_assignable<B, A>::value
         << endl;

    // Check if struct B is assignable to
    // srtuct B or not
    cout << "is class B = class B? "
         << is_nothrow_assignable<B, B>::value
         << endl;

    // Check if enum class AB is assignable
    // from class gfg or not
    cout << "is class AB = class gfg? "
         << is_nothrow_assignable<AB, gfg>::value
         << endl;

    // Check if class GfG assignable to
    // class gfg or not
    cout << "is class Gfg = class gfg? "
         << is_nothrow_assignable<GfG, gfg>::value
         << endl;
    return 0;
}

Output:

is int = double? true
is struct A = struct A? true
is class B = class A? true
is class B = class B? false
is class AB = class gfg? false
is class Gfg = class gfg? false

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