std::is_move_constructible, std::is_trivially_move_constructible, std::is_nothrow_move_constructible

From Cppreference

Defined in header `<type_traits>`

template< class T > struct is_move_constructible;	(1)	(C++11 feature)

template< class T > struct is_trivially_move_constructible;	(2)	(C++11 feature)

template< class T > struct is_nothrow_move_constructible;	(3)	(C++11 feature)

1) If the constructor expression T(arg); is well-formed for arg of type T&& (that is, T is a scalar or reference or a class with an accessible move constructor), provides the member constant value equal true. For any other type, value is false.

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

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

Inherited from std::integral_constant

Member constants


`value`	true if `T` is move-constructible , 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] Notes

Move constructors are usually noexcept, since otherwise they are unusable in any code that provides strong exception guarantee.

[edit] Equivalent definition

template< class T>
struct is_move_constructible :
        std::is_constructible<T, typename std::add_rvalue_reference<T>::type> {};
 
template< class T>
struct is_trivially_move_constructible :
       std::is_trivially_constructible<T, typename std::add_rvalue_reference<T>::type> {};
 
template< class T>
struct is_nothrow_move_constructible :
       std::is_nothrow_constructible<T, typename std::add_rvalue_reference<T>::type> {};

[edit] Example

#include <iostream>
#include <type_traits>
 
struct Ex1 {
    std::string str; // member has a non-trivial but non-throwing move ctor
};
struct Ex2 {
    int n;
    Ex2(Ex2&&) = default; // trivial and non-throwing
};
 
int main() {
    std::cout << std::boolalpha << "Ex1 is move-constructible? "
              << std::is_move_constructible<Ex1>::value << '\n'
              << "Ex1 is trivially move-constructible? "
              << std::is_trivially_move_constructible<Ex1>::value << '\n'
              << "Ex1 is nothrow move-constructible? "
              << std::is_nothrow_move_constructible<Ex1>::value << '\n'
              << "Ex2 is trivially move-constructible? "
              << std::is_trivially_move_constructible<Ex2>::value << '\n'
              << "Ex2 is nothrow move-constructible? "
              << std::is_nothrow_move_constructible<Ex2>::value << '\n';
}

Output:

Ex1 is move-constructible? true
Ex1 is trivially move-constructible? false
Ex1 is nothrow move-constructible? true
Ex2 is trivially move-constructible? true
Ex2 is nothrow move-constructible? true

[edit] See also

is_constructible is_trivially_constructible is_nothrow_constructible (C++11)
(C++11)
(C++11)

checks if a type has a constructor for specific arguments
(class template)

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)

move_if_noexcept (C++11)

obtains an rvalue reference if the move constructor does not throw
(function template)