std::execution::read_env

 

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)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Execution control library

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>
inlineconstexpr/*unspecified*/ read_env{};		(since C++26) (customization point object)
Call signature
execution::senderauto read_env(auto&& query );		(since C++26)

A sender factory that returns a sender that reaches into a receiver’s environment and pulls out the current value associated with a given query object.

For any query object q, the expression read_env(q) is expression-equivalent to /*make-sender*/(read_env, q).

Customization point objects

The name execution::read_env denotes a customization point object, which is a const function object of a literalsemiregular class type. See CustomizationPointObject for details.

Example

An example usage of this factory is to schedule dependent work on the receiver's scheduler, which can be obtained with read_env(get_scheduler):

std::execution::senderauto task = std::execution::read_env(std::execution::get_scheduler)| std::execution::let_value([](auto sched){return std::execution::starts_on(sched, /*some nested work here*/);});   std::this_thread::sync_wait( std::move(task));// wait for it to finish