[exec.continues.on]

# 33 Execution control library [[exec]](./#exec)

## 33.9 Senders [[exec.snd]](exec.snd#exec.continues.on)

### 33.9.12 Sender adaptors [[exec.adapt]](exec.adapt#exec.continues.on)

#### 33.9.12.6 execution​::​continues_on [exec.continues.on]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3289)

continues_on adapts a sender into one
that completes on the specified scheduler[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3293)

The name continues_on denotes a pipeable sender adaptor object[.](#2.sentence-1)

For subexpressions sch and sndr,
if decltype((sch)) does not satisfy [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]"), ordecltype((sndr)) does not satisfy [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]"),continues_on(sndr, sch) is ill-formed[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3300)

Otherwise,
the expression continues_on(sndr, sch) is expression-equivalent to:transform_sender(*get-domain-early*(sndr), *make-sender*(continues_on, sch, sndr)) except that sndr is evaluated only once[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3308)

The exposition-only class template *impls-for* ([[exec.snd.expos]](exec.snd.expos "33.9.2 Exposition-only entities"))
is specialized for continues_on_t as follows:namespace std::execution {template<>struct *impls-for*<continues_on_t> : *default-impls* {static constexpr auto *get-attrs* =[](const auto& data, const auto& child) noexcept -> decltype(auto) {return *JOIN-ENV*(*SCHED-ATTRS*(data), *FWD-ENV*(get_env(child))); }; };}

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3323)

Let sndr and env be subexpressions
such that Sndr is decltype((sndr))[.](#5.sentence-1)

If [*sender-for*](exec.snd.concepts#concept:sender-for "33.9.3 Sender concepts [exec.snd.concepts]")<Sndr, continues_on_t> is false,
then
the expression continues_on.transform_sender(sndr, env) is ill-formed;
otherwise, it is equal to:auto [_, data, child] = sndr;return schedule_from(std::move(data), std::move(child));

[*Note [1](#note-1)*:

This causes the continues_on(sndr, sch) sender to becomeschedule_from(sch, sndr) when it is connected with a receiver
whose execution domain does not customize continues_on[.](#5.sentence-2)

— *end note*]

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3340)

Let out_sndr be a subexpression denoting
a sender returned from continues_on(sndr, sch) or one equal to such, and
let OutSndr be the type decltype((out_sndr))[.](#6.sentence-1)

Let out_rcvr be a subexpression denoting a receiver
that has an environment of type Env such that [sender_in](exec.snd.concepts#concept:sender_in "33.9.3 Sender concepts [exec.snd.concepts]")<OutSndr, Env> is true[.](#6.sentence-2)

Let op be an lvalue referring to the operation state
that results from connecting out_sndr with out_rcvr[.](#6.sentence-3)

Calling start(op) shall
start sndr on the current execution agent and
execute completion operations on out_rcvr on an execution agent of the execution resource associated with sch[.](#6.sentence-4)

If scheduling onto sch fails,
an error completion on out_rcvr shall be executed
on an unspecified execution agent[.](#6.sentence-5)