std::execution::just_error

 

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Execution concepts scheduler receiver receiver_of operation_state    sender sender_in sender_to Execution components Execution contexts run_loop Execution domains default_domain Forward progress guarantee forward_progress_guarantee Environments empty_env    get_env    env_of_t Queries std::stop_token_of_t std::get_stop_token std::get_allocator std::forwarding_query get_scheduler get_domain get_forward_progress_guarantee get_delegation_scheduler get_completion_scheduler Completion signatures completion_signatures completion_signatures_of_t transform_completion_signatures transform_completion_signatures_of    value_types_of_t error_types_of_t    tag_of_t sends_stopped    Sender adaptor closures sender_adaptor_closure Coroutine utility as_awaitable with_awaitable_senders

Core operations Operation state connect connect_result_t start Completion set_value set_error set_stopped Transformation transform_env transform_sender apply_sender Sender algorithms Sender factories just just_error just_stopped read_env schedule schedule_result_t Sender adaptors starts_on continues_on    on then upon_error upon_stopped let_value let_error let_stopped schedule_from when_all when_all_with_variant into_variant stopped_as_optional stopped_as_error bulk split Sender consumers this_thread::sync_wait this_thread::sync_wait_with_variant

 

Defined in header <execution>
inline constexpr just_error_t just_error{}; struct just_error_t { /*unspecified*/ };		(since C++26) (customization point object)
Call signature
execution::sender auto just_error( auto&& error );		(since C++26)

A sender factory that returns a sender which completes immediately by calling the receiver’s set_error().

Let e be a subexpression represented by an input error which will be injected and returned by the receiver. The expression just_error(e) is expression-equivalent to /*make-sender*/(just_error, /*product-type*/(e))

Customization point objects

The name execution::just_error denotes a customization point object, which is a const function object of a literal semiregular class type. The cv-unqualified version of its type is a tag type denoted as execution::just_error_t.

All instances of execution::just_error_t are equal. The effects of invoking different instances of type execution::just_error_t on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, execution::just_error can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to execution::just_error above, execution::just_error_t models

• std::invocable<execution::just_error_t, Args...>,
• std::invocable<const execution::just_error_t, Args...>,
• std::invocable<execution::just_error_t&, Args...>, and
• std::invocable<const execution::just_error_t&, Args...>.
  

Otherwise, no function call operator of execution::just_error_t participates in overload resolution.

Notes

If the provided error is an lvalue reference, a copy is made inside the returned sender and a non-const lvalue reference to the copy is sent to the receiver’s set_error. If the provided value is an rvalue reference, it is moved into the returned sender and an rvalue reference to it is sent to the receiver’s set_error.