C++11: Reference Collapsing

When the compiler changes ‘references to references’ into ‘references’ in certain situations.

Example:

Typedef A  B;

Typedef B  C;

C       var; // Var is type A

--

Typedef A& B;

Typedef B  C;

C       var; // Var is type A&

--

Typedef A  B;

Typedef B& C;

C       var; // Var is type A&

--

Typedef A&  B;

Typedef B&  C;

C       var; // Var is type A&

--

Typedef A&&  B;

Typedef B&&  C;

C       var;  // Var is type A&&

--

Reference collapsing can also happen with decltype specifiers and template type parameters. Reference Collapsing for References (&) existed pre-C++11.  Reference Collapsing for Rvalue References was added in C++11.

https://www.ibm.com/support/knowledgecenter/en/SSGH3R_13.1.0/com.ibm.xlcpp131.aix.doc/language_ref/reference_collapsing.html