tmp/tmpn56mgcl5/{from.md → to.md}
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| 1 |
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#### `execution::continues_on` <a id="exec.continues.on">[[exec.continues.on]]</a>
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`continues_on` adapts a sender into one that completes on the specified
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scheduler.
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The name `continues_on` denotes a pipeable sender adaptor object. For
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subexpressions `sch` and `sndr`, if `decltype((sch))` does not satisfy
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`scheduler`, or `decltype((sndr))` does not satisfy `sender`,
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`continues_on(sndr, sch)` is ill-formed.
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Otherwise, the expression `continues_on(sndr, sch)` is
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expression-equivalent to:
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``` cpp
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transform_sender(get-domain-early(sndr), make-sender(continues_on, sch, sndr))
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```
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except that `sndr` is evaluated only once.
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The exposition-only class template *`impls-for`* [[exec.snd.expos]] is
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specialized for `continues_on_t` as follows:
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``` cpp
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namespace std::execution {
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template<>
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struct impls-for<continues_on_t> : default-impls {
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static constexpr auto get-attrs =
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[](const auto& data, const auto& child) noexcept -> decltype(auto) {
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return JOIN-ENV(SCHED-ATTRS(data), FWD-ENV(get_env(child)));
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};
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};
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}
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```
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Let `sndr` and `env` be subexpressions such that `Sndr` is
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`decltype((sndr))`. If `sender-for<Sndr, continues_on_t>` is `false`,
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then the expression `continues_on.transform_sender(sndr, env)` is
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ill-formed; otherwise, it is equal to:
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``` cpp
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auto [_, data, child] = sndr;
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return schedule_from(std::move(data), std::move(child));
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```
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[*Note 1*: This causes the `continues_on(sndr, sch)` sender to become
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`schedule_from(sch, sndr)` when it is connected with a receiver whose
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execution domain does not customize `continues_on`. — *end note*]
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Let `out_sndr` be a subexpression denoting a sender returned from
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`continues_on(sndr, sch)` or one equal to such, and let `OutSndr` be the
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type `decltype((out_sndr))`. Let `out_rcvr` be a subexpression denoting
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a receiver that has an environment of type `Env` such that
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`sender_in<OutSndr, Env>` is `true`. Let `op` be an lvalue referring to
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the operation state that results from connecting `out_sndr` with
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`out_rcvr`. Calling `start(op)` shall start `sndr` on the current
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execution agent and execute completion operations on `out_rcvr` on an
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execution agent of the execution resource associated with `sch`. If
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scheduling onto `sch` fails, an error completion on `out_rcvr` shall be
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executed on an unspecified execution agent.
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