[refwrap.const]

# 22 General utilities library [[utilities]](./#utilities)

## 22.10 Function objects [[function.objects]](function.objects#refwrap.const)

### 22.10.6 Class template reference_wrapper [[refwrap]](refwrap#const)

#### 22.10.6.2 Constructors [refwrap.const]

[🔗](#lib:reference_wrapper,constructor)

`template<class U>
  constexpr reference_wrapper(U&& u) noexcept(see below);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L11724)

Let *FUN* denote the exposition-only functionsvoid *FUN*(T&) noexcept;void *FUN*(T&&) = delete;

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L11731)

*Constraints*: The expression *FUN*(declval<U>()) is well-formed andis_same_v<remove_cvref_t<U>, reference_wrapper> is false[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L11736)

*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[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L11743)

*Remarks*: The exception specification is equivalent tonoexcept(*FUN*(declval<U>()))[.](#4.sentence-1)

[🔗](#lib:reference_wrapper,constructor_)

`constexpr reference_wrapper(const reference_wrapper& x) noexcept;
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L11755)

*Effects*: Constructs a reference_wrapper object that
stores a reference to x.get()[.](#5.sentence-1)