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

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Defined in header <type_traits>
template< class T >
struct is_move_constructible;
(1) (since C++11)
template< class T >
struct is_trivially_move_constructible;
(2) (since C++11)
template< class T >
struct is_nothrow_move_constructible;
(3) (since C++11)

1) Checks whether a type is MoveConstructible, that is, can be constructed from rvalue argument. If the requirement is met, a member constant value equal to true is provided; otherwise the 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.

Contents

Inherited from std::integral_constant

Member constants

value
[static]
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)
operator()
(C++14)
returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>
[edit template]

[edit] Notes

Types without a move constructor, but with a copy constructor that accepts const T& arguments, satisfy std::is_move_constructible.

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

[edit] Possible implementation

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

checks if a type has a constructor for specific arguments
(class template) [edit]
checks if a type has a default constructor
(class template) [edit]
checks if a type has a copy constructor
(class template) [edit]
obtains an rvalue reference if the move constructor does not throw
(function template) [edit]