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std::polymorphic<T, Allocator>:: valueless_after_move

From cppreference.net
Memory management library
( exposition only* )
Allocators
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Memory resources
Uninitialized storage (until C++20)
( until C++20* )
( until C++20* )
( until C++20* )

Garbage collector support (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
constexpr bool valueless_after_move ( ) const noexcept ;
(C++26以降)

* this が値を持たない状態かどうかをチェックします。

戻り値

true * this が値を持たない場合、それ以外の場合は false を返す。