cppdraft_translate/cppdraft/exec/stop/when.md

[exec.stop.when]

33 Execution control library [exec]

33.9 Senders [exec.snd]

33.9.12 Sender adaptors [exec.adapt]

33.9.12.17 Exposition-only execution​::​stop-when [exec.stop.when]

1

#

stop-when fuses an additional stop token t into a sender so that, upon connecting to a receiver r, the resulting operation state receives stop requests from botht and the token returned from get_stop_token(get_env(r)).

2

#

The name stop-when denotes an exposition-only sender adaptor.

For subexpressions sndr and token:

• (2.1)

  If decltype((sndr)) does not satisfy sender, orremove_cvref_t<decltype((token))> does not satisfy stoppable_token, then stop-when(sndr, token) is ill-formed.

• (2.2)

  Otherwise, if remove_cvref_t<decltype((token))> modelsunstoppable_token thenstop-when(​sndr, token) is expression-equivalent tosndr.

• (2.3)

  Otherwise,stop-when(sndr, token) returns a sender osndr. If osndr is connected to a receiver r, let rtoken be the result of get_stop_token(get_env(r)).

  • (2.3.1)

    If the type of rtoken models unstoppable_token then the effects of connecting osndr to r are equivalent toconnect(write_env(sndr, prop(get_stop_token, token)), r).

  • (2.3.2)

    Otherwise, the effects of connecting osndr to r are equivalent toconnect(write_env(sndr, prop(get_stop_token, stoken)), r) where stoken is an object of an exposition-only type stoken-t such that: + (2.3.2.1) stoken-t models stoppable_token;

    • [(2.3.2.2)](#2.3.2.2)
      

stoken.stop_requested() returns token.stop_requested() || rtoken.stop_reques-
ted();

+
      [(2.3.2.3)](#2.3.2.3)

stoken.stop_possible() returns token.stop_possible() || rtoken.stop_possible(); and

+
      [(2.3.2.4)](#2.3.2.4)

for types Fn and Init such that both invocable and constructible_from<Fn, Init> are modeled, stoken-t​::​callback_type models stoppable-callback-for<Fn, stoken-t, Init>. [Note 1: For an object fn of type Fn constructed from a value, init, of type Init, registering fn using stoken-t​::​callback_type(stoken, init) results in an invocation of fn when a callback registered with token or rtoken would be invoked. fn is invoked at most once. — end note]