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integrate wording from P3164
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@ericniebler
ericniebler committed Mar 29, 2024
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Showing 1 changed file with 118 additions and 50 deletions.
168 changes: 118 additions & 50 deletions execution.bs
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Expand Up @@ -5521,7 +5521,9 @@ template<class C>
sender with a receiver that has an environment of type `Env`. <span
class="wg21note">The type of the receiver does not affect an asychronous
operation's completion signatures, only the type of the receiver's
environment.</span>
environment.</span> A sender type whose completion signatures are knowable
independent of an execution environment is known as a <dfn
export=true>non-dependent sender</dfn>.

14. A <dfn export=true>sender algorithm</dfn> is a function that takes and/or
returns a sender. There are three categories of sender algorithms:
Expand Down Expand Up @@ -5641,7 +5643,7 @@ namespace std::execution {
template&lt;class Sndr>
concept sender = <i>see below</i>;

template&lt;class Sndr, class Env = empty_env>
template&lt;class Sndr, class... Env>
concept sender_in = <i>see below</i>;

template&lt;class Sndr, class Rcvr>
Expand All @@ -5660,9 +5662,9 @@ namespace std::execution {
struct get_completion_signatures_t;
inline constexpr get_completion_signatures_t get_completion_signatures {};

template&lt;class Sndr, class Env = empty_env>
requires sender_in&lt;Sndr, Env>
using completion_signatures_of_t = <i>call-result-t</i>&lt;get_completion_signatures_t, Sndr, Env>;
template&lt;class Sndr, class... Env>
requires sender_in&lt;Sndr, Env...>
using completion_signatures_of_t = <i>call-result-t</i>&lt;get_completion_signatures_t, Sndr, Env...>;

template&lt;class... Ts>
using <i>decayed-tuple</i> = tuple&lt;decay_t&lt;Ts>...>; // exposition only
Expand Down Expand Up @@ -6762,12 +6764,13 @@ namespace std::execution {
move_constructible&lt;remove_cvref_t&lt;Sndr>> && <i>// rvalues are movable, and</i>
constructible_from&lt;remove_cvref_t&lt;Sndr>, Sndr>; <i>// lvalues are copyable</i>

template&lt;class Sndr, class Env = empty_env>
template&lt;class Sndr, class... Env>
concept sender_in =
sender&lt;Sndr> &&
queryable&lt;Env> &&
requires (Sndr&& sndr, Env&& env) {
{ get_completion_signatures(std::forward&lt;Sndr>(sndr), std::forward&lt;Env>(env)) }
(sizeof...(Env) <= 1)
(queryable&lt;Env> &&...) &&
requires (Sndr&& sndr, Env&&... env) {
{ get_completion_signatures(std::forward&lt;Sndr>(sndr), std::forward&lt;Env>(env)...) }
-> <i>valid-completion-signatures</i>;
};

Expand Down Expand Up @@ -6871,8 +6874,13 @@ namespace std::execution {
is an lvalue referring to the coroutine's promise type, `Promise`. <span
class="wg21note">This includes the invocation of the promise type's
`await_transform` member if any, the invocation of the `operator co_await`
picked by overload resolution if any, and any necessary implicit
conversions and materializations.</span>
picked by overload resolution if any, and any necessary implicit conversions
and materializations.</span> Let <code><i>GET-AWAITER</i>(c)</code> be
expression-equivalent to <code><i>GET-AWAITER</i>(c, q)</code> where `q` is
an lvalue of an unspecified empty class type <i>`none-such`</i> that lacks
an `await_transform` member, and where
<code>coroutine_handle&lt;<i>none-such</i>></code> behaves as
`coroutine_handle<void>`.

<span class="ed-note">I have opened
[cwg#250](https://github.com/cplusplus/CWG/issues/250) to give these
Expand All @@ -6886,18 +6894,18 @@ namespace std::execution {
template&lt;class T>
concept <i>await-suspend-result</i> = <i>see below</i>;

template&lt;class A, class Promise>
template&lt;class A, class... Promise>
concept <i>is-awaiter</i> = <i>// exposition only</i>
requires (A& a, coroutine_handle&lt;Promise> h) {
requires (A& a, coroutine_handle&lt;Promise...> h) {
a.await_ready() ? 1 : 0;
{ a.await_suspend(h) } -> <i>await-suspend-result</i>;
a.await_resume();
};

template&lt;class C, class Promise>
template&lt;class C, class... Promise>
concept <i>is-awaitable</i> =
requires (C (*fc)() noexcept, Promise& p) {
{ <i>GET-AWAITER</i>(fc(), p) } -> <i>is-awaiter</i>&lt;Promise>;
requires (C (*fc)() noexcept, Promise&... p) {
{ <i>GET-AWAITER</i>(fc(), p...) } -> <i>is-awaiter</i>&lt;Promise...>;
};
}
</pre>
Expand All @@ -6911,7 +6919,9 @@ namespace std::execution {

4. For a subexpression `c` such that `decltype((c))` is type `C`, and
an lvalue `p` of type `Promise`, <code><i>await-result-type</i>&lt;C, Promise></code>
denotes the type <code>decltype(<i>GET-AWAITER</i>(c, p).await_resume())</code>.
denotes the type <code>decltype(<i>GET-AWAITER</i>(c, p).await_resume())</code>,
and <code><i>await-result-type</i>&lt;C></code> denotes the type
<code>decltype(<i>GET-AWAITER</i>(c).await_resume())</code>.

5. Let <i>`with-await-transform`</i> be the exposition-only class template:

Expand Down Expand Up @@ -7098,30 +7108,64 @@ namespace std::execution {

### `execution::get_completion_signatures` <b>[exec.getcomplsigs]</b> ### {#spec-execution.getcomplsigs}

1. `get_completion_signatures` is a customization point object. Let `sndr` be an
expression such that `decltype((sndr))` is `Sndr`, and let `env` be an
expression such that `decltype((env))` is `Env`. Then
`get_completion_signatures(sndr, env)` is expression-equivalent to:
1. `get_completion_signatures` is a customization point object. For a
subexpression `sndr`, let `Sndr` be `decltype((sndr))`. Then
`get_completion_signatures(sndr)` is expression-equivalent to:

1. `decltype(sndr.get_completion_signatures(env)){}` if that
expression is well-formed,
1. `remove_cvref_t<Sndr>::completion_signatures()` if that expression is
well-formed,

2. Otherwise, `remove_cvref_t<Sndr>::completion_signatures{}` if that expression is well-formed,
2. Otherwise, `decltype(sndr.get_completion_signatures())()` if that
expression is well-formed,

3. Otherwise, if <code><i>is-awaitable</i>&lt;Sndr, <i>env-promise</i>&lt;Env>></code>
3. Otherwise, if <code><i>is-awaitable</i>&lt;Sndr></code>
is `true`, then:

<pre highlight="c++">
completion_signatures<
<i>SET-VALUE-SIG</i>(<i>await-result-type</i>&lt;Sndr,
<i>env-promise</i>&lt;Env>>), <i>// see [exec.snd.concepts]</i>
set_error_t(exception_ptr),
set_stopped_t()>{}
</pre>
<pre highlight="c++">
completion_signatures<
<i>SET-VALUE-SIG</i>(<i>await-result-type</i>&lt;Sndr>), <i>// see [exec.snd.concepts]</i>
set_error_t(exception_ptr),
set_stopped_t()>()
</pre>

4. Otherwise, `get_completion_signatures(sndr)` is ill-formed.

2. For a subexpression `env`, let `Env` be `decltype((env))`. Then
`get_completion_signatures(sndr, env)` is expression-equivalent to:

1. `remove_cvref_t<Sndr>::completion_signatures()` if that expression is
well-formed,

2. Otherwise, `decltype(sndr.get_completion_signatures(env))()` if that
expression is well-formed,

3. Otherwise, if <code><i>is-awaitable</i>&lt;Sndr,
<i>env-promise</i>&lt;Env>></code> is `true`, then:

<pre highlight="c++">
completion_signatures<
<i>SET-VALUE-SIG</i>(<i>await-result-type</i>&lt;Sndr,
<i>env-promise</i>&lt;Env>>), <i>// see [exec.snd.concepts]</i>
set_error_t(exception_ptr),
set_stopped_t()>()
</pre>

4. Otherwise, `get_completion_signatures(sndr, env)` is ill-formed.

2. Let `rcvr` be an rvalue receiver of type `Rcvr`, and let `Sndr` be the type of a
3. If `get_completion_signatures(sndr)` is well-formed and its type denotes a
specialization of the `completion_signatures` class template, then `Sndr` is
a non-dependent sender type ([async.ops]).

4. Given a pack of subexpressions `se`, the expression
`get_completion_signatures(se...)` is ill-formed if `sizeof...(se)` is less
than `1` or greater than `2`.

5. If `completion_signatures_of_t<Sndr>` and `completion_signatures_of_t<Sndr,
Env>` are both well-formed, they shall denote the same set of completion
signatures, disregarding the order of signatures and rvalue reference
qualification of arguments.

6. Let `rcvr` be an rvalue receiver of type `Rcvr`, and let `Sndr` be the type of a
sender such that `sender_in<Sndr, env_of_t<Rcvr>>` is `true`. Let `Sigs...` be the
template arguments of the `completion_signatures` specialization named by
`completion_signatures_of_t<Sndr, env_of_t<Rcvr>>`. Let <i>`CSO`</i> be
Expand Down Expand Up @@ -7157,7 +7201,7 @@ namespace std::execution {
[[noreturn]] void return_void() noexcept { terminate(); }

coroutine_handle<> unhandled_stopped() noexcept {
set_stopped((DR&&) <i>rcvr</i>);
set_stopped(std::move(<i>rcvr</i>));
return noop_coroutine();
}

Expand Down Expand Up @@ -7376,6 +7420,10 @@ namespace std::execution {
`exception_ptr` argument, the implementation is allowed to omit the
`exception_ptr` error completion signature from the set.

7. Unless otherwise specified, an adaptor whose child senders are all
non-dependent ([async.ops]) is itself non-dependent. This requirement applies
to any function that is selected by the implementation of the sender adaptor.

#### Sender adaptor closure objects <b>[exec.adapt.objects]</b> #### {#spec-execution.senders.adaptor.objects}

1. A <i>pipeable sender adaptor closure object</i> is a function object that
Expand Down Expand Up @@ -7722,13 +7770,22 @@ namespace std::execution {
of the invocable as a value completion.

2. The names `then`, `upon_error`, and `upon_stopped` denote customization point
objects. Let the expression <i>`then-cpo`</i> be one of `then`,
`upon_error`, or `upon_stopped`. For subexpressions `sndr` and `f`, let `Sndr` be
`decltype((sndr))` and let `F` be the decayed type of `f`. If `Sndr` does not
satisfy `sender`, or `F` does not satisfy <i>`movable-value`</i>,
objects. For `then`, `upon_error`, and `upon_stopped`, let <i>`set-cpo`</i>
be `set_value`, `set_error`, and `set_stopped` respectively. Let the
expression <i>`then-cpo`</i> be one of `then`, `upon_error`, or
`upon_stopped`. For subexpressions `sndr` and `f`, let `Sndr` be
`decltype((sndr))` and let `F` be the decayed type of `f`. If `Sndr` does
not satisfy `sender`, or `F` does not satisfy <i>`movable-value`</i>,
<code><i>then-cpo</i>(sndr, f)</code> is ill-formed.

3. Otherwise, the expression <code><i>then-cpo</i>(sndr, f)</code> is
3. Let <i>`invoke-result`</i> be an alias template such that
<code><i>invoke-result</i>&lt;Ts...></code> denotes the type
`invoke_result_t<F, Ts...>`. If `sender_in<Sndr>` is `true` and
<code><i>gather-signatures</i>&lt;tag_t&lt;<i>set-cpo</i>>,
completion_signatures_of_t&lt;Sndr>, <i>invoke-result</i>,
<i>type-list</i>></code> is ill-formed, the program is ill-formed.

4. Otherwise, the expression <code><i>then-cpo</i>(sndr, f)</code> is
expression-equivalent to:

<pre highlight="c++">
Expand All @@ -7737,10 +7794,8 @@ namespace std::execution {
<i>make-sender</i>(<i>then-cpo</i>, f, sndr));
</pre>

4. For `then`, `upon_error`, and `upon_stopped`, let <i>`set-cpo`</i>
be `set_value`, `set_error`, and `set_stopped` respectively. The
exposition-only class template <i>`impls-for`</i>
([exec.snd.general]) is specialized for <i>`then-cpo`</i> as follows:
5. The exposition-only class template <i>`impls-for`</i> ([exec.snd.general]) is
specialized for <i>`then-cpo`</i> as follows:

<pre highlight="c++">
namespace std::execution {
Expand Down Expand Up @@ -7806,9 +7861,15 @@ namespace std::execution {
<i>make-sender</i>(<i>let-cpo</i>, f, sndr));
</pre>

5. The exposition-only class template <i>`impls-for`</i>
([exec.snd.general]) is specialized for <i>`let-cpo`</i> as
follows:
5. Let <i>`invoke-result`</i> be an alias template such that
<code><i>invoke-result</i>&lt;Ts...></code> denotes the type
`invoke_result_t<F, Ts...>`. If `sender_in<Sndr>` is `true` and
<code><i>gather-signatures</i>&lt;tag_t&lt;set-cpo>,
completion_signatures_of_t&lt;Sndr>, <i>invoke-result</i>,
<i>type-list</i>></code> is ill-formed, the program is ill-formed.

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

<pre highlight="c++">
namespace std::execution {
Expand Down Expand Up @@ -7917,7 +7978,7 @@ namespace std::execution {
env)</code> is ill-formed. Otherwise, it is equal to
<code><i>JOIN-ENV</i>(<i>let-env</i>(sndr), <i>FWD-ENV</i>(env))</code>.

7. Let the subexpression `out_sndr` denote the result of the invocation
8. Let the subexpression `out_sndr` denote the result of the invocation
<code><i>let-cpo</i>(sndr, f)</code> or an object copied or moved from such,
and let the subexpression `rcvr` denote a receiver such that the expression
`connect(out_sndr, rcvr)` is well-formed. The expression `connect(out_sndr,
Expand Down Expand Up @@ -7952,8 +8013,15 @@ namespace std::execution {
<i>make-sender</i>(bulk, <i>product-type</i>{shape, f}, sndr));
</pre>

4. The exposition-only class template <i>`impls-for`</i>
([exec.snd.general]) is specialized for `bulk_t` as follows:
4. Let <i>`invoke-result`</i> be an alias template such that
<code><i>invoke-result</i>&lt;Ts...></code> denotes the type
`invoke_result_t<F, Shape, Ts...>`. If `sender_in<Sndr>` is `true` and
<code><i>gather-signatures</i>&lt;tag_t&lt;set-cpo>,
completion_signatures_of_t&lt;Sndr>, <i>invoke-result</i>,
<i>type-list</i>></code> is ill-formed, the program is ill-formed.

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

<pre highlight="c++">
namespace std::execution {
Expand Down Expand Up @@ -7989,7 +8057,7 @@ namespace std::execution {
`true` if and only if `Tag` denotes a type other than `set_value_t`
or if the expression `f(auto(shape), args...)` is well-formed.

5. Let the subexpression `out_sndr` denote the result of the invocation
6. Let the subexpression `out_sndr` denote the result of the invocation
<code>bulk(sndr, shape, f)</code> or an object copied or moved from such,
and let the subexpression `rcvr` denote a receiver such that the expression
`connect(out_sndr, rcvr)` is well-formed. The expression `connect(out_sndr,
Expand Down

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