[expected.void.cons]

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

## 22.8 Expected objects [[expected]](expected#void.cons)

### 22.8.7 Partial specialization of expected for void types [[expected.void]](expected.void#cons)

#### 22.8.7.2 Constructors [expected.void.cons]

[🔗](#lib:expected%3cvoid%3e,constructor)

`constexpr expected() noexcept;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9539)

*Postconditions*: has_value() is true[.](#1.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor_)

`constexpr expected(const expected& rhs);
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9550)

*Effects*: If rhs.has_value() is false,
direct-non-list-initializes *unex* with rhs.error()[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9555)

*Postconditions*: rhs.has_value() == this->has_value()[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9559)

*Throws*: Any exception thrown by the initialization of *unex*[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9563)

*Remarks*: This constructor is defined as deleted
unless is_copy_constructible_v<E> is true[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9568)

This constructor is trivial
if is_trivially_copy_constructible_v<E> is true[.](#6.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor__)

`constexpr expected(expected&& rhs) noexcept(is_nothrow_move_constructible_v<E>);
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9579)

*Constraints*: is_move_constructible_v<E> is true[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9583)

*Effects*: If rhs.has_value() is false,
direct-non-list-initializes *unex* with std​::​move(rhs.error())[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9588)

*Postconditions*: rhs.has_value() is unchanged;rhs.has_value() == this->has_value() is true[.](#9.sentence-1)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9593)

*Throws*: Any exception thrown by the initialization of *unex*[.](#10.sentence-1)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9597)

*Remarks*: This constructor is trivial
if is_trivially_move_constructible_v<E> is true[.](#11.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor___)

`template<class U, class G>
  constexpr explicit(!is_convertible_v<const G&, E>) expected(const expected<U, G>& rhs);
template<class U, class G>
  constexpr explicit(!is_convertible_v<G, E>) expected(expected<U, G>&& rhs);
`

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9612)

Let GF be const G& for the first overload andG for the second overload[.](#12.sentence-1)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9616)

*Constraints*: 

- [(13.1)](#13.1)

is_void_v<U> is true; and

- [(13.2)](#13.2)

is_constructible_v<E, GF> is true; and

- [(13.3)](#13.3)

is_constructible_v<unexpected<E>, expected<U, G>&> is false; and

- [(13.4)](#13.4)

is_constructible_v<unexpected<E>, expected<U, G>> is false; and

- [(13.5)](#13.5)

is_constructible_v<unexpected<E>, const expected<U, G>&> is false; and

- [(13.6)](#13.6)

is_constructible_v<unexpected<E>, const expected<U, G>> is false[.](#13.sentence-1)

[14](#14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9637)

*Effects*: If rhs.has_value() is false,
direct-non-list-initializes *unex* with std​::​forward<GF>(rhs.error())[.](#14.sentence-1)

[15](#15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9643)

*Postconditions*: rhs.has_value() is unchanged;rhs.has_value() == this->has_value() is true[.](#15.sentence-1)

[16](#16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9648)

*Throws*: Any exception thrown by the initialization of *unex*[.](#16.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor____)

`template<class G>
  constexpr explicit(!is_convertible_v<const G&, E>) expected(const unexpected<G>& e);
template<class G>
  constexpr explicit(!is_convertible_v<G, E>) expected(unexpected<G>&& e);
`

[17](#17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9662)

Let GF be const G& for the first overload andG for the second overload[.](#17.sentence-1)

[18](#18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9666)

*Constraints*: is_constructible_v<E, GF> is true[.](#18.sentence-1)

[19](#19)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9670)

*Effects*: Direct-non-list-initializes *unex* with std​::​forward<GF>(e.error())[.](#19.sentence-1)

[20](#20)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9675)

*Postconditions*: has_value() is false[.](#20.sentence-1)

[21](#21)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9679)

*Throws*: Any exception thrown by the initialization of *unex*[.](#21.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor_____)

`constexpr explicit expected(in_place_t) noexcept;
`

[22](#22)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9690)

*Postconditions*: has_value() is true[.](#22.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor______)

`template<class... Args>
  constexpr explicit expected(unexpect_t, Args&&... args);
`

[23](#23)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9702)

*Constraints*: is_constructible_v<E, Args...> is true[.](#23.sentence-1)

[24](#24)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9706)

*Effects*: Direct-non-list-initializes *unex* with std​::​forward<Args>(args)...[.](#24.sentence-1)

[25](#25)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9711)

*Postconditions*: has_value() is false[.](#25.sentence-1)

[26](#26)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9715)

*Throws*: Any exception thrown by the initialization of *unex*[.](#26.sentence-1)

[🔗](#lib:expected%3cvoid%3e,constructor_______)

`template<class U, class... Args>
  constexpr explicit expected(unexpect_t, initializer_list<U> il, Args&&... args);
`

[27](#27)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9727)

*Constraints*: is_constructible_v<E, initializer_list<U>&, Args...> is true[.](#27.sentence-1)

[28](#28)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9731)

*Effects*: Direct-non-list-initializes *unex* with il, std​::​forward<Args>(args)...[.](#28.sentence-1)

[29](#29)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9736)

*Postconditions*: has_value() is false[.](#29.sentence-1)

[30](#30)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L9740)

*Throws*: Any exception thrown by the initialization of *unex*[.](#30.sentence-1)