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std::expected<T,E>::expected

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< cpp‎ | utility‎ | expected
 
 
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constexpr expected();
(1) (since C++23)
constexpr expected( const expected& other );
(2) (since C++23)
constexpr expected( expected&& other ) noexcept(/* see below */);
(3) (since C++23)
template< class U, class G >
constexpr explicit(/* see below */) expected( const expected<U, G>& other );
(4) (since C++23)
template< class U, class G >
constexpr explicit(/* see below */) expected( expected<U, G>&& other );
(5) (since C++23)
template< class U = T >
constexpr explicit(!std::is_convertible_v<U, T>) expected( U&& v );
(6) (since C++23)
(T is not cv void)
template< class G >

constexpr explicit(!std::is_convertible_v<const G&, E>)

    expected( const std::unexpected<G>& e );
(7) (since C++23)
template< class G >

constexpr explicit(!std::is_convertible_v<G, E>)

    expected( std::unexpected<G>&& e );
(8) (since C++23)
template< class... Args >
constexpr explicit expected( std::in_place_t, Args&&... args );
(9) (since C++23)
(T is not cv void)
template< class U, class... Args >

constexpr explicit expected( std::in_place_t,

                             std::initializer_list<U> il, Args&&... args );
(10) (since C++23)
(T is not cv void)
constexpr explicit expected( std::in_place_t ) noexcept;
(11) (since C++23)
(T is cv void)
template< class... Args >
constexpr explicit expected( std::unexpect_t, Args&&... args );
(12) (since C++23)
template< class U, class... Args >

constexpr explicit expected( std::unexpect_t,

                             std::initializer_list<U> il, Args&&... args );
(13) (since C++23)

Constructs a new expected object.

1) Default constructor. If T is not (possibly cv-qualified) void, constructs an object that contains an expected value, which is value-initialized.
After construction, has_value() returns true.
This overload participates in overload resolution only if T is (possibly cv-qualified) void or std::is_default_constructible_v<T> is true.
2) Copy constructor. If other.has_value() is false, the new object contains an unexpected value, which is direct-initialized from other.error(). Otherwise, if T is not (possibly cv-qualified) void, the new object contains an expected value, which is direct-initialized from *other.
After construction, has_value() is equal to other.has_value().
This constructor is defined as deleted unless
This constructor is trivial if
3) Move constructor. If other.has_value() is false, the new object contains an unexpected value, which is direct-initialized from std::move(other.error()). Otherwise, if T is not (possibly cv-qualified) void, the new object contains an expected value, which is direct-initialized from std::move(*other).
After construction, has_value() is equal to other.has_value().
This constructor participates in overload resolution only if
This constructor is trivial if
4,5) Let
If other.has_value() is false, the new object contains an unexpected value, which is direct-initialized from std::forward<GF>(other.error()). Otherwise, if T is not (possibly cv-qualified) void, the new object contains an expected value, which is direct-initialized from std::forward<UF>(*other).
After construction, has_value() is equal to other.has_value().
Each of these constructors does not participate in overload resolution unless the following conditions are met respectively:
These constructors are explicit if std::is_convertible_v<UF, T> or std::is_convertible_v<GF, E> is false.
6) Constructs an object that contains an expected value, initialized as if direct-initializing (but not direct-list-initializing) an object of type T with the expression std::forward<U>(v).
After construction, has_value() returns true.
This constructor does not participate in overload resolution unless the following conditions are met:
7,8) Let GF be const G& for (7) and G for (8). Constructs an object that contains an unexpected value, which is direct-initialized from std::forward<GF>(e.error()).
After construction, has_value() returns false.
These overloads participate in overload resolution only if std::is_constructible_v<E, GF> is true.
9) Constructs an object that contains an expected value, which is direct-initialized from the arguments std::forward<Args>(args)....
After construction, has_value() returns true.
This overload participates in overload resolution only if std::is_constructible_v<T, Args...> is true.
10) Constructs an object that contains an expected value, which is direct-initialized from the arguments il, std::forward<Args>(args)....
After construction, has_value() returns true.
This overload participates in overload resolution only if std::is_constructible_v<T, std::initializer_list<U>&, Args...> is true.
11) Constructs an object such that after construction, has_value() returns true.
12) Constructs an object that contains an unexpected value, which is direct-initialized from the arguments std::forward<Args>(args)....
After construction, has_value() returns false.
This overload participates in overload resolution only if std::is_constructible_v<E, Args...> is true.
13) Constructs an object that contains an unexpected value, which is direct-initialized from the arguments il, std::forward<Args>(args)....
After construction, has_value() returns false.
This overload participates in overload resolution only if std::is_constructible_v<E, std::initializer_list<U>&, Args...> is true.

Contents

[edit] Parameters

other - another expected object whose contained value is copied
e - std::unexpected object whose contained value is copied
v - value with which to initialize the contained value
args... - arguments with which to initialize the contained value
il - initializer list with which to initialize the contained value

[edit] Exceptions

1) Throws any exception thrown by the constructor of T.
If T is (possibly cv-qualified) void,
noexcept specification:  
noexcept
  
2) Throws any exception thrown by the constructor of T or E.
3) If T is (possibly cv-qualified) void,
noexcept specification:  
Otherwise,
4,5) Throws any exception thrown by the constructor of T or E.
6) Throws any exception thrown by the constructor of T.
7,8) Throws any exception thrown by the constructor of E.
9,10) Throws any exception thrown by the constructor of T.
12,13) Throws any exception thrown by the constructor of E.

[edit] Example

[edit] See also

represented as an unexpected value
(class template) [edit]
in-place construction tag
(tag)[edit]
in-place construction tag for unexpected value in expected
(tag)[edit]