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Jun 27, 2024
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rename read to read_env #253

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57 changes: 14 additions & 43 deletions execution.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -388,7 +388,7 @@ struct dynamic_buffer { //
sender_of<dynamic_buffer> auto async_read_array(auto handle) { // 2
return just(dynamic_buffer{}) // 4
| let_value([handle] (dynamic_buffer& buf) { // 5
return just(std::as_writeable_bytes(std::span(&buf.size, 1)) // 6
return just(std::as_writeable_bytes(std::span(&buf.size, 1))) // 6
| async_read(handle) // 7
| then( // 8
[&buf] (std::size_t bytes_read) { // 9
Expand Down Expand Up @@ -3196,29 +3196,16 @@ execution::sender auto just_stopped();
Returns a sender with no [=completion scheduler|completion schedulers=], which
completes immediately by calling the receiver's `set_stopped`.

### `execution::read` ### {#design-sender-factory-read}
### `execution::read_env` ### {#design-sender-factory-read}

<pre highlight="c++">
execution::sender auto read(auto tag);

execution::sender auto get_scheduler() {
return read(execution::get_scheduler);
}
execution::sender auto get_delegation_scheduler() {
return read(execution::get_delegation_scheduler);
}
execution::sender auto get_allocator() {
return read(execution::get_allocator);
}
execution::sender auto get_stop_token() {
return read(execution::get_stop_token);
}
execution::sender auto read_env(auto tag);
</pre>

Returns a sender that reaches into a receiver's environment and pulls out the
current value associated with the customization point denoted by `Tag`. It then
sends the value read back to the receiver through the value channel. For
instance, `get_scheduler()` (with no arguments) is a sender that asks the
instance, `read_env(get_scheduler)` is a sender that asks the
receiver for the currently suggested `scheduler` and passes it to the receiver's
`set_value` completion-signal.

Expand All @@ -3228,7 +3215,7 @@ onto it.

<pre highlight="c++">
execution::sender auto task =
execution::get_scheduler()
execution::read_env(get_scheduler)
| execution::let_value([](auto sched) {
return execution::starts_on(sched, <i>some nested work here</i>);
});
Expand All @@ -3237,7 +3224,7 @@ onto it.
</pre>

This code uses the fact that `sync_wait` associates a scheduler with the
receiver that it connects with `task`. `get_scheduler()` reads that scheduler
receiver that it connects with `task`. `read_env(get_scheduler)` reads that scheduler
out of the receiver, and passes it to `let_value`'s receiver's `set_value`
function, which in turn passes it to the lambda. That lambda returns a new
sender that uses the scheduler to schedule some nested work onto `sync_wait`'s
Expand Down Expand Up @@ -5325,7 +5312,7 @@ template&lt;class Initializer>
<td>allow the specialization of the provided sender algorithms</td>
<td>
<ul>
<li>sender factories (e.g., `schedule`, `just`, `read`)</li>
<li>sender factories (e.g., `schedule`, `just`, `read_env`)</li>
<li>sender adaptors (e.g., `continues_on`, `then`, `let_value`)</li>
<li>sender consumers (e.g., `start_detached`, `sync_wait`)</li>
</ul>
Expand Down Expand Up @@ -6001,10 +5988,6 @@ namespace std::execution {
3. `forwarding_query(get_allocator)` is a core constant expression and has value
`true`.

4. `get_allocator()` (with no arguments) is expression-equivalent to
`execution::read(get_allocator)` ([exec.read]).



### `get_stop_token` <b>[exec.get.stop.token]</b> ### {#spec-execution.get_stop_token}

Expand All @@ -6024,9 +6007,6 @@ namespace std::execution {
3. `forwarding_query(get_stop_token)` is a core constant
expression and has value `true`.

4. `get_stop_token()` (with no arguments) is expression-equivalent to
`execution::read(get_stop_token)` ([exec.read]).

### `execution::get_env` <b>[exec.get.env]</b> ### {#spec-execution.environment.get_env}

1. `execution::get_env` is a customization point object. For a subexpression
Expand Down Expand Up @@ -6057,9 +6037,6 @@ namespace std::execution {
3. `forwarding_query(execution::get_domain)` is a core constant
expression and has value `true`.

4. `get_domain()` (with no arguments) is expression-equivalent to
`execution::read(get_domain)` ([exec.read]).

### `execution::get_scheduler` <b>[exec.get.scheduler]</b> ### {#spec-execution.get_scheduler}

1. `get_scheduler` asks a queryable object for its associated scheduler.
Expand All @@ -6074,9 +6051,6 @@ namespace std::execution {
3. `forwarding_query(execution::get_scheduler)` is a core constant
expression and has value `true`.

4. `get_scheduler()` (with no arguments) is expression-equivalent to
`execution::read(get_scheduler)` ([exec.read]).

### `execution::get_delegation_scheduler` <b>[exec.get.delegation.scheduler]</b> ### {#spec-execution.get_delegation_scheduler}

1. `get_delegation_scheduler` asks a queryable object for a scheduler that can be
Expand All @@ -6093,9 +6067,6 @@ namespace std::execution {
3. `forwarding_query(execution::get_delegation_scheduler)` is a core
constant expression and has value `true`.

4. `get_delegation_scheduler()` (with no arguments) is expression-equivalent to
`execution::read(get_delegation_scheduler)` ([exec.read]).

### `execution::get_forward_progress_guarantee` <b>[exec.get.forward.progress.guarantee]</b> ### {#spec-execution.get_forward_progress_guarantee}

<pre highlight="c++">
Expand Down Expand Up @@ -7521,23 +7492,23 @@ namespace std::execution {
}
</pre>

#### `execution::read` <b>[exec.read]</b> #### {#spec-execution.senders.read}
#### `execution::read_env` <b>[exec.read.env]</b> #### {#spec-execution.senders.read.env}

1. `read` is a sender factory for a sender whose asynchronous operation
1. `read_env` is a sender factory for a sender whose asynchronous operation
completes synchronously in its start operation with a value completion
result equal to a value read from the receiver's associated environment.

2. `read` is a customization point object. For some query object `q`,
the expression `read(q)` is expression-equivalent to
<code><i>make-sender</i>(read, q)</code>.
2. `read_env` is a customization point object. For some query object `q`,
the expression `read_env(q)` is expression-equivalent to
<code><i>make-sender</i>(read_env, q)</code>.

3. The exposition-only class template <i>`impls-for`</i> ([exec.snd.general])
is specialized for `read` as follows:
is specialized for `read_env` as follows:

<pre highlight="c++">
namespace std::execution {
template&lt;>
struct <i>impls-for</i>&lt;<i>decayed-typeof</i>&lt;read>> : <i>default-impls</i> {
struct <i>impls-for</i>&lt;<i>decayed-typeof</i>&lt;read_env>> : <i>default-impls</i> {
static constexpr auto <em>start</em> =
[](auto query, auto& rcvr) noexcept -> void {
<i>TRY-SET-VALUE</i>(rcvr, query(get_env(rcvr)));
Expand Down