Constant as rvalue in C++(11)

Question

Why const int is not an R-value in C++(11)? I thought that R-value was \'anything\' which cannot be on the left hand side and constants fulfil that

Answer 1

The parameter type is an rvalue reference and the standard forbids initialization of an rvalue-reference with an lvalue of a "reference-related" type.

8.5.3 References [dcl.init.ref ]

...

5 ... If T1 is reference-related to T2 and the reference is an rvalue reference, the initializer expression shall not be an lvalue.

Hence, the following is an error:

void f (long &&);

const long x = 1;
void g () { f (x); }

But the following is not:

void f (long &&);

const int x = 1;
void g () { f (x); }

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So, the reason for the error is not simply "the initialization is not with an rvalue", but because "the initialization is with an lvalue of a reference-related type."