operator==(std::expected)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)    is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

std::expected

Member functions

expected::expected (C++23)

expected::~expected (C++23)

expected::operator= (C++23)

Observers

expected::operator->expected::operator* (C++23)(C++23)

expected::operator boolexpected::has_value (C++23)(C++23)

expected::value (C++23)

expected::error (C++23)

expected::value_or (C++23)

Monadic operations

expected::and_then (C++23)

expected::or_else (C++23)

expected::transform (C++23)

expected::transform_error (C++23)

Modifiers

expected::emplace (C++23)

expected::swap (C++23)

Non-member functions

operator== (C++23)

swap (C++23)

Helper classes

unexpected (C++23)

bad_expected_access (C++23)

unexpect_tunexpect (C++23)(C++23)

 

template< class T2, class E2 >   requires (!std::is_void_v<T2>) friend constexpr bool operator==( const expected& lhs,                                   const std::expected<T2, E2>& rhs );	(1)	(since C++23) (T is not cv void)
template< class T2, class E2 >   requires std::is_void_v<T2> friend constexpr bool operator==( const expected& lhs,                                   const std::expected<T2, E2>& rhs );	(2)	(since C++23) (T is cv void)
template< class T2 > friend constexpr bool operator==( const expected& x, const T2& val );	(3)	(since C++23) (T is not cv void)
template< class E2 > friend constexpr bool operator==( const expected& x,                                   const unexpected<E2>& e );	(4)	(since C++23)

Performs comparison operations on expected objects.

1,2) Compares two expected objects. The objects compare equal if and only if lhs.has_value() and rhs.has_value() are equal, and the contained values are equal.

• For overload (1), if the expressions *lhs == *rhs and lhs.error() == rhs.error() are not well-formed, or if their results are not convertible to bool, the program is ill-formed.
• For overload (2), if the expressions lhs.error() == rhs.error() is not well-formed, or if its result is not convertible to bool, the program is ill-formed.

3) Compares expected object with a value. The objects compare equal if and only if x contains an expected value, and the contained value is equal to val.

• If the expression *x == val is not well-formed, or if its result is not convertible to bool, the program is ill-formed.

4) Compares expected object with an unexpected value. The objects compare equal if and only if x contains an unexpected value, and the contained value is equal to e.error().

• If the expression x.error() == e.error() is not well-formed, or if its result is not convertible to bool, the program is ill-formed.

These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::expected<T, E> is an associated class of the arguments.

The != operator is synthesized from operator==.

Parameters

lhs, rhs, x	-	expected object to compare
val	-	value to compare to the expected value contained in x
e	-	value to compare to the unexpected value contained in x

Return value

1) If lhs.has_value() != rhs.has_value(), returns false. Otherwise, if lhs.has_value() is true, returns *lhs == *rhs. Otherwise, returns lhs.error() ==  rhs.error().

2) If lhs.has_value() != rhs.has_value(), returns false. Otherwise, if lhs.has_value() is true, returns true. Otherwise, returns lhs.error() ==  rhs.error().

3) Returns x.has_value() && static_cast<bool>(*x == val).

4) Returns !x.has_value() && static_cast<bool>(x.error() == e.error()).

Exceptions

Throws when and what the comparison throws.

See also

unexpected (C++23)

represented as an unexpected value (class template)