what is the && means at the end of a function

Question

I am confused when reading this page

struct S
{
    virtual int f(char) const, g(int) &&; // declares two non-static member functions
    virtual int f(char), x; // compile-time error: virtual (in decl-specifier-seq)
                            // is only allowed in declarations of non-static
                            // member functions
};

What is the

virtual int g(int) &&;

means about ?

score 1 · Accepted Answer · answered Aug 09 '19 at 09:32

&& at the end of the function mean that the function is chosen when this has r-value value category.

See member functions:

A non-static member function can be declared with no ref-qualifier, with an lvalue ref-qualifier (the token & after the parameter list) or the rvalue ref-qualifier (the token && after the parameter list). During overload resolution, non-static cv-qualified member function of class X is treated as follows:

no ref-qualifier: the implicit object parameter has type lvalue reference to cv-qualified X and is additionally allowed to bind rvalue implied object argument

lvalue ref-qualifier: the implicit object parameter has type lvalue reference to cv-qualified X

rvalue ref-qualifier: the implicit object parameter has type rvalue reference to cv-qualified X

what is the && means at the end of a function

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