std::is_move_constructible, std::is_trivially_move_constructible, std::is_nothrow_move_constructible
| 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) If T is not a referenceable type (i.e., possibly cv-qualified void or a function type with a cv-qualifier-seq or a ref-qualifier), provides a member constant value equal to false. Otherwise, provides a member constant value equal to std::is_constructible<T, T&&>::value.
2) Same as (1), but uses std::is_trivially_constructible<T, T&&>.
3) Same as (1), but uses std::is_nothrow_constructible<T, T&&>.
T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined.
| Contents | 
[edit] Helper variable templates
| template< class T > inline constexpr bool is_move_constructible_v = is_move_constructible<T>::value; | (since C++17) | |
| template< class T > inline constexpr bool is_trivially_move_constructible_v = is_trivially_move_constructible<T>::value; | (since C++17) | |
| template< class T > inline constexpr bool is_nothrow_move_constructible_v = is_nothrow_move_constructible<T>::value; | (since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] | true if Tis 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] 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] 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.
In many implementations, is_nothrow_move_constructible also checks if the destructor throws because it is effectively noexept(T(arg)). Same applies to is_trivially_move_constructible, which, in these implementations, also requires that the destructor is trivial: GCC bug 51452 LWG issue 2116.
[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 }; struct NoMove { // prevents implicit declaration of default move constructor // however, the class is still move-constructible because its // copy constructor can bind to an rvalue argument NoMove(const NoMove&) {} }; 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'; std::cout << std::boolalpha << "NoMove is move-constructible? " << std::is_move_constructible<NoMove>::value << '\n' << "NoMove is nothrow move-constructible? " << std::is_nothrow_move_constructible<NoMove>::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 NoMove is move-constructible? true NoMove is nothrow move-constructible? false
[edit] See also
| (C++11)(C++11)(C++11) | checks if a type has a constructor for specific arguments (class template) | 
| checks if a type has a default constructor (class template) | |
| (C++11)(C++11)(C++11) | checks if a type has a copy constructor (class template) | 
| (C++11) | obtains an rvalue reference if the move constructor does not throw (function template) | 


