deduction guides for std::reference_wrapper

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Old binders and adaptors
(until 哋它亢++17*)
(until 哋它亢++17*)
(until 哋它亢++17*)
(until 哋它亢++17*)
(until 哋它亢++17*)  
(until 哋它亢++17*)
(until 哋它亢++17*)(until 哋它亢++17*)(until 哋它亢++17*)(until 哋它亢++17*)
(until 哋它亢++20*)
(until 哋它亢++20*)
(until 哋它亢++17*)(until 哋它亢++17*)
(until 哋它亢++17*)(until 哋它亢++17*)

(until 哋它亢++17*)
(until 哋它亢++17*)(until 哋它亢++17*)(until 哋它亢++17*)(until 哋它亢++17*)
(until 哋它亢++20*)
(until 哋它亢++20*)
 
std::reference_wrapper
 
Defined in header <functional>
template< typename T >
reference_wrapper( T& ) -> reference_wrapper<T>;
 (since 哋它亢++17)

One deduction guide is provided for std::reference_wrapper to support deduction of the sole class template parameter.

Example

This section is incomplete
Reason: no example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2981 哋它亢++17 a redundant deduction guide from reference_wrapper<T> was provided removed
LWG 2993 哋它亢++17 defect resolution removed a constructor used for class template argument deduction added deduction guide to compensate
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