std::is_move_constructible, std::is_trivially_move_constructible, std::is_nothrow_move_constructible
From cppreference.com
Defined in header
<type_traits>
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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]
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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)
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returns value (public member function) |
Member types
Type | Definition |
value_type
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bool
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type
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std::integral_constant<bool, value> |
[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
Run this code
#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)
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checks if a type has a constructor for specific arguments (class template) |
checks if a type has a default constructor (class template) |
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(C++11)(C++11)(C++11)
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checks if a type has a copy constructor (class template) |
(C++11)
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obtains an rvalue reference if the move constructor does not throw (function template) |
(library fundamentals TS)
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variable template alias of std::is_move_constructible::value (variable template) |
(library fundamentals TS)
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variable template alias of std::is_trivially_move_constructible::value (variable template) |
(library fundamentals TS)
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variable template alias of std::is_nothrow_move_constructible::value (variable template) |