21 Metaprogramming library [meta]

21.3 Metaprogramming and type traits [type.traits]

21.3.8 Transformations between types [meta.trans]

21.3.8.3 Reference modifications [meta.trans.ref]

1
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The templates specified in Table 51 add or remove references.
Table 51: Reference modifications [tab:meta.trans.ref]
Template
Comments
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]