xvalue

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An xvalue (eXpiring value) expression is an expression which has identity and represents an object which can be implicitly moved from. The general idea with xvalue expressions is that the object they represent is going to be destroyed soon (hence the “eXpiring” part), and therefore implicitly moving from them is fine.

Given:

struct X { int n; };
extern X x;

4;                   // prvalue: does not have an identity
x;                   // lvalue
x.n;                 // lvalue
std::move(x);        // xvalue
std::forward<X&>(x); // lvalue
X{4};                // prvalue: does not have an identity
X{4}.n;              // xvalue: does have an identity and denotes resources
                     // that can be reused

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