std:: unexpect_t, std:: unexpect

From cppreference.com

Defined in header `<expected>`
struct unexpect_t { explicit unexpect_t ( ) = default ; } ;	(1)	(since C++23)
inline constexpr std :: unexpect_t unexpect { } ;	(2)	(since C++23)

1) A tag type for in-place construction of an unexpected value in an


        std::expected

object.

2) A constant of type const std :: unexpect_t which is usually directly passed to a constructor of


        std::expected

to construct an unexpected value.

Like other construction tag types, unexpect_t is a trivial, empty class with an explicit default constructor.

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)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

Member functions
expected::expected
expected::~expected
expected::operator=
Observers
expected::operator-> expected::operator*
expected::operator bool expected::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_t unexpect

(constructor)	constructs the `expected` object (public member function)
in_place in_place_type in_place_index in_place_t in_place_type_t in_place_index_t (C++17)	in-place construction tag (tag)