[refwrap.const] - C++17 → C++20

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tmp/tmp4h0li6i4/{from.md → to.md} RENAMED Viewed

@@ -1,16 +1,31 @@
-#### `reference_wrapper` construct/copy/destroy <a id="refwrap.const">[[refwrap.const]]</a>
 ``` cpp
-reference_wrapper(T& t) noexcept;
 ```
-*Effects:* Constructs a `reference_wrapper` object that stores a
-reference to `t`.
 ``` cpp
-reference_wrapper(const reference_wrapper& x) noexcept;
 ```
 *Effects:* Constructs a `reference_wrapper` object that stores a
 reference to `x.get()`.

+#### Constructors and destructor <a id="refwrap.const">[[refwrap.const]]</a>
 ``` cpp
+template<class U>
+  constexpr reference_wrapper(U&& u) noexcept(see below);
 ```
+Let *FUN* denote the exposition-only functions
 ``` cpp
+void FUN(T&) noexcept;
+void FUN(T&&) = delete;
+```
+*Constraints:* The expression *FUN*(declval\<U\>()) is well-formed and
+`is_same_v<remove_cvref_t<U>, reference_wrapper>` is `false`.
+*Effects:* Creates a variable `r` as if by `T& r = std::forward<U>(u)`,
+then constructs a `reference_wrapper` object that stores a reference to
+`r`.
+*Remarks:* The expression inside `noexcept` is equivalent to
+`noexcept(`*`FUN`*`(declval<U>()))`.
+``` cpp
+constexpr reference_wrapper(const reference_wrapper& x) noexcept;
 ```
 *Effects:* Constructs a `reference_wrapper` object that stores a
 reference to `x.get()`.

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