Move-constructs an `init_value` `x` from the element pointed to by `position`, erases the element and returns `x`.
Move-constructs an `init_value` `x` from the element pointed to by `position`, erases the element and returns从 `position` 指向的元素移动构造一个 `init_value` 对象 `x`，擦除该元素并返回 `x`.。
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Move-constructs an `init_value` `x` from the element pointed to by `position`, erases the element and returns从 `position` 指向的元素移动构造一个 `init_value` 对象 `x`，擦除该元素并返回 `x`.。