Why Doesn't `f(T&&)` Get Called When Passing an Rvalue Reference to It?

Why rvalue References Variables are Not rvalue References

Consider two overloads of a function f:

void f(T&&&); // #1
void f(T&);  // #2

In another function g:

void g(T&& t) 
{ 
  f(t);  // calls #2
}

Why does the overload f(T&) get called despite the parameter t being an rvalue?

The Nature of rvalue References

Rvalue references are variables that can only bind to rvalues (objects without names). T&&t has a name, making it an lvalue.

Distinction between Type and Value

T&& is the type rvalue reference. An rvalue reference can bind only to rvalues, but it is otherwise an lvalue of reference type.

Special Cases

• static_cast<T&&>(t): This explicitly creates an rvalue reference, enabling the call to f(T&&).

Rules Governing Rvalue References

• Implicit moves occur when returning named values from functions or when values have no names.
• Rvalue references or const& can only bind to rvalues.
• Reference lifetime extension applies to temporaries bound to references outside constructors.
• In certain contexts, T&& collapses to X& or X const& if T is X& or X const&.
• T&& can act as a "forwarding reference" in type deduction.

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