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[meta.trans.ref]

21 Metaprogramming library [meta]

21.3 Metaprogramming and type traits [type.traits]

21.3.9 Transformations between types [meta.trans]

21.3.9.3 Reference modifications [meta.trans.ref]

The templates specified in Table 58 add or remove references.

Table 58 — Reference modifications [tab:meta.trans.ref]

template<class T>
struct remove_reference;

If T has type “reference to T1” then the member typedef type denotes T1; otherwise, type denotes T.

template<class T>
struct add_lvalue_reference;

If T is a referenceable type ([defns.referenceable]) then the member typedef type denotes T&; otherwise, type denotes T.

[Note 1: 

This rule reflects the semantics of reference collapsing ([dcl.ref]).

— end note]

template<class T>
struct add_rvalue_reference;

If T is a referenceable type then the member typedef type denotes T&&; otherwise, type denotes T.

[Note 2: 

This rule reflects the semantics of reference collapsing ([dcl.ref]).

For example, when a type T is a reference type T1&, the type add_rvalue_reference_t<T> is not an rvalue reference.

— end note]