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cppdraft/exec/snd/general.md

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+[exec.snd.general]
+
+# 33 Execution control library [[exec]](./#exec)
+
+## 33.9 Senders [[exec.snd]](exec.snd#general)
+
+### 33.9.1 General [exec.snd.general]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1325)
+
+Subclauses [[exec.factories]](exec.factories "33.9.11 Sender factories") and [[exec.adapt]](exec.adapt "33.9.12 Sender adaptors") define
+customizable algorithms that return senders[.](#1.sentence-1)
+
+Each algorithm has a default implementation[.](#1.sentence-2)
+
+Let sndr be the result of an invocation of such an algorithm or
+an object equal to the result ([[concepts.equality]](concepts.equality "18.2 Equality preservation")), and
+let Sndr be decltype((sndr))[.](#1.sentence-3)
+
+Let rcvr be a receiver of type Rcvr with associated environment env of type Env such that [sender_to](exec.snd.concepts#concept:sender_to "33.9.3 Sender concepts [exec.snd.concepts]")<Sndr, Rcvr> is true[.](#1.sentence-4)
+
+For the default implementation of the algorithm that produced sndr,
+connecting sndr to rcvr and
+starting the resulting operation state ([[exec.async.ops]](exec.async.ops "33.3 Asynchronous operations"))
+necessarily results in the potential evaluation ([[basic.def.odr]](basic.def.odr "6.3 One-definition rule")) of
+a set of completion operations
+whose first argument is a subexpression equal to rcvr[.](#1.sentence-5)
+
+Let Sigs be a pack of completion signatures corresponding to
+this set of completion operations, and
+let CS be
+the type of the expression get_completion_signatures<Sndr, Env>()[.](#1.sentence-6)
+
+Then CS is
+a specialization of
+the class template completion_signatures ([[exec.cmplsig]](exec.cmplsig "33.10 Completion signatures")),
+the set of whose template arguments is Sigs[.](#1.sentence-7)
+
+If none of the types in Sigs are dependent on the type Env, then
+the expression get_completion_signatures<Sndr>() is well-formed and
+its type is CS[.](#1.sentence-8)
+
+If a user-provided implementation of the algorithm
+that produced sndr is selected instead of the default:
+
+- [(1.1)](#1.1)
+
+  Any completion signature
+that is in the set of types
+denoted by completion_signatures_of_t<Sndr, Env> and
+that is not part of Sigs shall correspond to
+error or stopped completion operations,
+unless otherwise specified[.](#1.1.sentence-1)
+
+- [(1.2)](#1.2)
+
+  If none of the types in Sigs are dependent on the type Env, thencompletion_signatures_of_t<Sndr> andcompletion_signatures_of_t<Sndr, Env> shall denote the same type[.](#1.2.sentence-1)