[exec.into.variant]

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

## 33.9 Senders [[exec.snd]](exec.snd#exec.into.variant)

### 33.9.12 Sender adaptors [[exec.adapt]](exec.adapt#exec.into.variant)

#### 33.9.12.13 execution​::​into_variant [exec.into.variant]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4722)

into_variant adapts a sender with multiple value completion signatures
into a sender with just one value completion signature
consisting of a variant of tuples[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4727)

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

For a subexpression sndr, let Sndr be decltype((sndr))[.](#2.sentence-2)

If Sndr does not satisfy [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]"),into_variant(sndr) is ill-formed[.](#2.sentence-3)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4733)

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

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4741)

The exposition-only class template *impls-for* ([[exec.snd.expos]](exec.snd.expos "33.9.2 Exposition-only entities"))
is specialized for into_variant as follows:

[🔗](#lib:impls-for%3cinto_variant_t%3e)

namespace std::execution {template<>struct *impls-for*<into_variant_t> : *default-impls* {static constexpr auto *get-state* = *see below*; static constexpr auto *complete* = *see below*; template<class Sndr, class... Env>static consteval void *check-types*() {auto cs = get_completion_signatures<*child-type*<Sndr>, *FWD-ENV-T*(Env)...>(); *decay-copyable-result-datums*(cs); // see [[exec.snd.expos]](exec.snd.expos "33.9.2 Exposition-only entities")}};}

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4762)

The member *impls-for*<into_variant_t>​::​*get-state* is initialized with a callable object equivalent to the following lambda:[]<class Sndr, class Rcvr>(Sndr&& sndr, Rcvr& rcvr) noexcept-> type_identity<value_types_of_t<*child-type*<Sndr>, *FWD-ENV-T*(env_of_t<Rcvr>)>> {return {};}

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4772)

The member *impls-for*<into_variant_t>​::​*complete* is initialized with a callable object equivalent to the following lambda:[]<class State, class Rcvr, class Tag, class... Args>(auto, State, Rcvr& rcvr, Tag, Args&&... args) noexcept -> void {if constexpr ([same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<Tag, set_value_t>) {using variant_type = typename State::type; *TRY-SET-VALUE*(rcvr, variant_type(*decayed-tuple*<Args...>{std::forward<Args>(args)...})); } else { Tag()(std::move(rcvr), std::forward<Args>(args)...); }}