std::is_constructible, std::is_trivially_constructible, std::is_nothrow_constructible

From cppreference.com

Defined in header `<type_traits>`

template< class T, class... Args > struct is_constructible;	(1)	(since C++11)

template< class T, class... Args > struct is_trivially_constructible;	(2)	(since C++11)

template< class T, class... Args > struct is_nothrow_constructible;	(3)	(since C++11)

1) If the expression T obj(arg1, arg2, ... argN); is well-formed, given rvalue references to Args... as arguments, provides the member constant value equal true. For any other type, value is false.

2) same as 1), but the constructor expression does not call any operation that is not trivial.

3) same as 1), but the constructor expression is noexcept.

Inherited from std::integral_constant

Member constants


value [static]	true if `T` is constructible from `Args...` , false otherwise (public static member constant)

Member functions


operator bool	converts the object to bool, returns `value` (public member function)

Member types


Type	Definition

`value_type`	`bool`

`type`	std::integral_constant<bool, value>

[edit] Example

run this code

#include <iostream>
#include <type_traits>
 
class Foo {
    int v1;
    double v2;
 public:
    Foo(int n) : v1(n), v2() {}
    Foo(int n, double f) noexcept : v1(n), v2(f) {}
};
 
int main() {
    std::cout << "Foo is ...\n" << std::boolalpha
              << "\tTrivially-constructible from const Foo&? "
              << std::is_trivially_constructible<Foo, const Foo&>::value << '\n'
              << "\tTrivially-constructible from int? "
              << std::is_trivially_constructible<Foo, int>::value << '\n'
              << "\tConstructible from int? "
              << std::is_constructible<Foo, int>::value << '\n'
              << "\tNothrow-constructible from int? "
              << std::is_nothrow_constructible<Foo, int>::value << '\n'
              << "\tNothrow-constructible from int and double? "
              << std::is_nothrow_constructible<Foo, int, double>::value << '\n';
}

Output:

Foo is ...
        Trivially-constructible from const Foo&? true
        Trivially-constructible from int? false
        Constructible from int? true
        Nothrow-constructible from int? false
        Nothrow-constructible from int and double? true

[edit] See also


is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11) (C++11) (C++11)	checks if a type has a default constructor (class template)

is_copy_constructible is_trivially_copy_constructible is_nothrow_copy_constructible (C++11) (C++11) (C++11)	checks if a type has a copy constructor (class template)

is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11) (C++11) (C++11)	checks if a type has a move constructor (class template)

uses_allocator (C++11)	checks if the specified type supports uses-allocator construction (class template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)