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

 

C++

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Standard library headers

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Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

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Containers library

Iterators library

Ranges library (C++20)

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Numerics library

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Filesystem library (C++17)

Regular expressions library (C++11)

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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) Debugging support is_debugger_present (C++26) breakpoint_if_debugging (C++26) breakpoint (C++26) Three-way comparison 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_ltis_lteq (C++20)(C++20)(C++20) is_neqis_gtis_gteq (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) to_chars_result (C++17) from_chars_result (C++17)

 

std::expected

Member functions

expected::expected

expected::~expected

expected::operator=

Observers

expected::operator->expected::operator*

expected::operator boolexpected::has_value

expected::value

expected::error

expected::value_or

expected::error_or

Monadic operations

expected::and_then

expected::or_else

expected::transform

expected::transform_error

Modifiers

expected::emplace

expected::swap

Non-member functions

operator==(std::expected)

swap(std::expected)

Helper classes

unexpected

bad_expected_access

unexpect_tunexpect

 

Primary template
template< class... Args > constexpr T& emplace( Args&&... args ) noexcept;	(1)	(since C++23)
template< class U, class... Args > constexpr T& emplace( std::initializer_list<U> il, Args&&... args ) noexcept;	(2)	(since C++23)
void partial specialization
constexpr void emplace() noexcept;	(3)	(since C++23)

Constructs an expected value in-place. After the call, has_value() returns true.

1) Destroys the contained value, then direct-initializes the expected value contained in *this with std::forward<Args>(args)....

This overload participates in overload resolution only if std::is_nothrow_constructible_v<T, Args...> is true.

2) Destroys the contained value, then direct-initializes the expected value contained in *this with il and std::forward<Args>(args)....

This overload participates in overload resolution only if std::is_nothrow_constructible_v<T, std::initializer_list<U>&, Args...> is true.

3) If *this contains an unexpected value, destroys that value.

Parameters

args	-	the arguments to pass to the constructor
il	-	the initializer list to pass to the constructor

Return value

1) *std::construct_at(std::addressof(val), std::forward<Args>(args)...)

2) *std::construct_at(std::addressof(val), il, std::forward<Args>(args)...)

Notes

If the construction of T is potentially-throwing, operator= can be used instead.

See also

operator=

assigns contents (public member function)