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cppdraft/exec/adapt/general.md

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+[exec.adapt.general]
+
+# 33 Execution control library [[exec]](./#exec)
+
+## 33.9 Senders [[exec.snd]](exec.snd#exec.adapt.general)
+
+### 33.9.12 Sender adaptors [[exec.adapt]](exec.adapt#general)
+
+#### 33.9.12.1 General [exec.adapt.general]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3002)
+
+Subclause [[exec.adapt]](exec.adapt "33.9.12 Sender adaptors") specifies a set of sender adaptors[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3005)
+
+The bitwise inclusive or operator is overloaded
+for the purpose of creating sender chains[.](#2.sentence-1)
+
+The adaptors also support function call syntax with equivalent semantics[.](#2.sentence-2)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3010)
+
+Unless otherwise specified:
+
+- [(3.1)](#3.1)
+
+  A sender adaptor is prohibited from causing observable effects,
+apart from moving and copying its arguments,
+before the returned sender is connected with a receiver using connect,
+and start is called on the resulting operation state[.](#3.1.sentence-1)
+
+- [(3.2)](#3.2)
+
+  A parent sender ([[exec.async.ops]](exec.async.ops "33.3 Asynchronous operations")) with a single child sender sndr has
+an associated attribute object equal to*FWD-ENV*(get_env(sndr)) ([[exec.fwd.env]](exec.fwd.env "33.5.1 forwarding_­query"))[.](#3.2.sentence-1)
+
+- [(3.3)](#3.3)
+
+  A parent sender with more than one child sender has
+an associated attributes object equal to env<>{}[.](#3.3.sentence-1)
+
+- [(3.4)](#3.4)
+
+  When a parent sender is connected to a receiver rcvr,
+any receiver used to connect a child sender has
+an associated environment equal to *FWD-ENV*(get_env(rcvr))[.](#3.4.sentence-1)
+
+- [(3.5)](#3.5)
+
+  An adaptor whose child senders are all non-dependent ([[exec.async.ops]](exec.async.ops "33.3 Asynchronous operations"))
+is itself non-dependent[.](#3.5.sentence-1)
+
+- [(3.6)](#3.6)
+
+  These requirements apply to any function
+that is selected by the implementation of the sender adaptor[.](#3.6.sentence-1)
+
+- [(3.7)](#3.7)
+
+  *Recommended practice*: Implementations should use
+the completion signatures of the adaptors
+to communicate type errors to users and
+to propagate any such type errors from child senders[.](#3.7.sentence-1)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3043)
+
+If a sender returned from a sender adaptor specified in [[exec.adapt]](exec.adapt "33.9.12 Sender adaptors") is specified to include set_error_t(Err) among its set of completion signatures
+where decay_t<Err> denotes the type exception_ptr,
+but the implementation does not potentially evaluate
+an error completion operation with an exception_ptr argument,
+the implementation is allowed to omit
+the exception_ptr error completion signature from the set[.](#4.sentence-1)

cppdraft/exec/adapt/obj.md

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+[exec.adapt.obj]
+
+# 33 Execution control library [[exec]](./#exec)
+
+## 33.9 Senders [[exec.snd]](exec.snd#exec.adapt.obj)
+
+### 33.9.12 Sender adaptors [[exec.adapt]](exec.adapt#obj)
+
+#### 33.9.12.2 Closure objects [exec.adapt.obj]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3055)
+
+A [*pipeable sender adaptor closure object*](#def:sender_adaptor_closure_object,pipeable "33.9.12.2 Closure objects [exec.adapt.obj]") is a function object
+that accepts one or more [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") arguments and returns a [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]")[.](#1.sentence-1)
+
+For a pipeable sender adaptor closure object c and
+an expression sndr such that decltype((sndr)) models [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]"),
+the following expressions are equivalent and yield a [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]"):c(sndr) sndr | c
+
+Given an additional pipeable sender adaptor closure object d,
+the expression c | d produces
+another pipeable sender adaptor closure object e:
+
+e is a perfect forwarding call wrapper ([[func.require]](func.require "22.10.4 Requirements"))
+with the following properties:
+
+- [(1.1)](#1.1)
+
+  Its target object is an object d2 of type decltype(auto(d)) direct-non-list-initialized with d[.](#1.1.sentence-1)
+
+- [(1.2)](#1.2)
+
+  It has one bound argument entity,
+an object c2 of type decltype(auto(c)) direct-non-list-initialized with c[.](#1.2.sentence-1)
+
+- [(1.3)](#1.3)
+
+  Its call pattern is d2(c2(arg)),
+where arg is the argument used in a function call expression of e[.](#1.3.sentence-1)
+
+The expression c | d is well-formed if and only if
+the initializations of the state entities ([[func.def]](func.def "22.10.3 Definitions")) of e are all well-formed[.](#1.sentence-5)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3088)
+
+An object t of type T is
+a pipeable sender adaptor closure object
+if T models [derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<sender_adaptor_closure<T>>,T has no other base classes
+of type sender_adaptor_closure<U> for any other type U, andT does not satisfy [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]")[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3096)
+
+The template parameter D for sender_adaptor_closure can be
+an incomplete type[.](#3.sentence-1)
+
+Before any expression of type cv D appears as
+an operand to the | operator,D shall be complete and
+model [derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<sender_adaptor_closure<D>>[.](#3.sentence-2)
+
+The behavior of an expression involving an object of type cv D as an operand to the | operator is undefined
+if overload resolution selects a program-defined operator| function[.](#3.sentence-3)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3107)
+
+A [*pipeable sender adaptor object*](#def:sender_adaptor_object,pipeable "33.9.12.2 Closure objects [exec.adapt.obj]") is a customization point object
+that accepts a [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") as its first argument and
+returns a [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]")[.](#4.sentence-1)
+
+If a pipeable sender adaptor object accepts only one argument,
+then it is a pipeable sender adaptor closure object[.](#4.sentence-2)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L3114)
+
+If a pipeable sender adaptor object adaptor accepts more than one argument,
+then let sndr be an expression
+such that decltype((sndr)) models [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]"),
+let args... be arguments
+such that adaptor(sndr, args...) is a well-formed expression
+as specified below, and
+let BoundArgs be a pack that denotes decltype(auto(args))...[.](#5.sentence-1)
+
+The expression adaptor(args...) produces
+a pipeable sender adaptor closure object f that is a perfect forwarding call wrapper with the following properties:
+
+- [(5.1)](#5.1)
+
+  Its target object is a copy of adaptor[.](#5.1.sentence-1)
+
+- [(5.2)](#5.2)
+
+  Its bound argument entities bound_args consist of
+objects of types BoundArgs... direct-non-list-initialized withstd​::​forward<decltype((args))>(args)..., respectively[.](#5.2.sentence-1)
+
+- [(5.3)](#5.3)
+
+  Its call pattern is adaptor(rcvr, bound_args...),
+where rcvr is
+the argument used in a function call expression of f[.](#5.3.sentence-1)
+
+The expression adaptor(args...) is well-formed if and only if
+the initializations of the bound argument entities of the result,
+as specified above, are all well-formed[.](#5.sentence-3)