[support.coroutine]

# 17 Language support library [[support]](./#support)

## 17.13 Coroutines [support.coroutine]

### [17.13.1](#general) General [[support.coroutine.general]](support.coroutine.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5749)

The header <coroutine> defines several types providing
compile and run-time support for
coroutines in a C++ program[.](#general-1.sentence-1)

### [17.13.2](#coroutine.syn) Header <coroutine> synopsis [[coroutine.syn]](coroutine.syn)

[🔗](#header:%3ccoroutine%3e_)

// all freestanding#include <compare> // see [[compare.syn]](compare.syn "17.12.1 Header <compare> synopsis")namespace std {// [[coroutine.traits]](#coroutine.traits "17.13.3 Coroutine traits"), coroutine traitstemplate<class R, class... ArgTypes>struct coroutine_traits; // [[coroutine.handle]](#coroutine.handle "17.13.4 Class template coroutine_­handle"), coroutine handletemplate<class Promise = void>struct coroutine_handle; // [[coroutine.handle.compare]](#coroutine.handle.compare "17.13.4.8 Comparison operators"), comparison operatorsconstexpr bool operator==(coroutine_handle<> x, coroutine_handle<> y) noexcept; constexpr strong_ordering operator<=>(coroutine_handle<> x, coroutine_handle<> y) noexcept; // [[coroutine.handle.hash]](#coroutine.handle.hash "17.13.4.9 Hash support"), hash supporttemplate<class T> struct hash; template<class P> struct hash<coroutine_handle<P>>; // [[coroutine.noop]](#coroutine.noop "17.13.5 No-op coroutines"), no-op coroutinesstruct noop_coroutine_promise; template<> struct coroutine_handle<noop_coroutine_promise>; using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;

 noop_coroutine_handle noop_coroutine() noexcept; // [[coroutine.trivial.awaitables]](#coroutine.trivial.awaitables "17.13.6 Trivial awaitables"), trivial awaitablesstruct suspend_never; struct suspend_always;}

### [17.13.3](#coroutine.traits) Coroutine traits [[coroutine.traits]](coroutine.traits)

#### [17.13.3.1](#coroutine.traits.general) General [[coroutine.traits.general]](coroutine.traits.general)

[1](#coroutine.traits.general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5798)

Subclause [[coroutine.traits]](#coroutine.traits "17.13.3 Coroutine traits") defines requirements on classes representing[*coroutine traits*](#def:coroutine_traits),
and defines the class templatecoroutine_traits that meets those requirements[.](#coroutine.traits.general-1.sentence-1)

#### [17.13.3.2](#coroutine.traits.primary) Class template coroutine_traits [[coroutine.traits.primary]](coroutine.traits.primary)

[1](#coroutine.traits.primary-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5808)

The header [<coroutine>](#header:%3ccoroutine%3e "17.13.2 Header <coroutine> synopsis [coroutine.syn]") defines the primary templatecoroutine_traits such that
if ArgTypes is a parameter pack of types and
if the [*qualified-id*](expr.prim.id.qual#nt:qualified-id "7.5.5.3 Qualified names [expr.prim.id.qual]") R​::​promise_type is valid and
denotes a type ([[temp.deduct]](temp.deduct "13.10.3 Template argument deduction")),
then coroutine_traits<R, ArgTypes...> has the following publicly
accessible member:using promise_type = typename R::promise_type;

Otherwise, coroutine_traits<R, ArgTypes...> has no members[.](#coroutine.traits.primary-1.sentence-2)

[2](#coroutine.traits.primary-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5822)

Program-defined specializations of this template shall define a publicly
accessible nested type named promise_type[.](#coroutine.traits.primary-2.sentence-1)

### [17.13.4](#coroutine.handle) Class template coroutine_handle [[coroutine.handle]](coroutine.handle)

#### [17.13.4.1](#coroutine.handle.general) General [[coroutine.handle.general]](coroutine.handle.general)

[🔗](#lib:coroutine_handle)

namespace std {template<>struct coroutine_handle<void>{// [[coroutine.handle.con]](#coroutine.handle.con "17.13.4.2 Construct/reset"), construct/resetconstexpr coroutine_handle() noexcept; constexpr coroutine_handle(nullptr_t) noexcept;
 coroutine_handle& operator=(nullptr_t) noexcept; // [[coroutine.handle.export.import]](#coroutine.handle.export.import "17.13.4.4 Export/import"), export/importconstexpr void* address() const noexcept; static constexpr coroutine_handle from_address(void* addr); // [[coroutine.handle.observers]](#coroutine.handle.observers "17.13.4.5 Observers"), observersconstexpr explicit operator bool() const noexcept; bool done() const; // [[coroutine.handle.resumption]](#coroutine.handle.resumption "17.13.4.6 Resumption"), resumptionvoid operator()() const; void resume() const; void destroy() const; private:void* ptr; // *exposition only*}; template<class Promise>struct coroutine_handle {// [[coroutine.handle.con]](#coroutine.handle.con "17.13.4.2 Construct/reset"), construct/resetconstexpr coroutine_handle() noexcept; constexpr coroutine_handle(nullptr_t) noexcept; static coroutine_handle from_promise(Promise&);
 coroutine_handle& operator=(nullptr_t) noexcept; // [[coroutine.handle.export.import]](#coroutine.handle.export.import "17.13.4.4 Export/import"), export/importconstexpr void* address() const noexcept; static constexpr coroutine_handle from_address(void* addr); // [[coroutine.handle.conv]](#coroutine.handle.conv "17.13.4.3 Conversion"), conversionconstexpr operator coroutine_handle<>() const noexcept; // [[coroutine.handle.observers]](#coroutine.handle.observers "17.13.4.5 Observers"), observersconstexpr explicit operator bool() const noexcept; bool done() const; // [[coroutine.handle.resumption]](#coroutine.handle.resumption "17.13.4.6 Resumption"), resumptionvoid operator()() const; void resume() const; void destroy() const; // [[coroutine.handle.promise]](#coroutine.handle.promise "17.13.4.7 Promise access"), promise access Promise& promise() const; private:void* ptr; // *exposition only*};}

[1](#coroutine.handle.general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5892)

An object of typecoroutine_handle<T> is called a [*coroutine handle*](#def:coroutine_handle) and can be used to refer to a suspended or executing coroutine[.](#coroutine.handle.general-1.sentence-1)

A coroutine_handle object whose
member address() returns a null pointer value
does not refer to any
coroutine[.](#coroutine.handle.general-1.sentence-2)

Two coroutine_handle objects refer to the same coroutine
if and only if their member address() returns the same non-null value[.](#coroutine.handle.general-1.sentence-3)

[2](#coroutine.handle.general-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5903)

If a program declares an explicit or partial specialization ofcoroutine_handle, the behavior is undefined[.](#coroutine.handle.general-2.sentence-1)

#### [17.13.4.2](#coroutine.handle.con) Construct/reset [[coroutine.handle.con]](coroutine.handle.con)

[🔗](#lib:coroutine_handle,constructor)

`constexpr coroutine_handle() noexcept;
constexpr coroutine_handle(nullptr_t) noexcept;
`

[1](#coroutine.handle.con-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5916)

*Postconditions*: address() == nullptr[.](#coroutine.handle.con-1.sentence-1)

[🔗](#lib:from_promise,coroutine_handle)

`static coroutine_handle from_promise(Promise& p);
`

[2](#coroutine.handle.con-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5927)

*Preconditions*: p is a reference to a promise object of a coroutine[.](#coroutine.handle.con-2.sentence-1)

[3](#coroutine.handle.con-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5931)

*Postconditions*: addressof(h.promise()) == addressof(p)[.](#coroutine.handle.con-3.sentence-1)

[4](#coroutine.handle.con-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5935)

*Returns*: A coroutine handle h referring to the coroutine[.](#coroutine.handle.con-4.sentence-1)

[🔗](#lib:operator=,coroutine_handle)

`coroutine_handle& operator=(nullptr_t) noexcept;
`

[5](#coroutine.handle.con-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5946)

*Postconditions*: address() == nullptr[.](#coroutine.handle.con-5.sentence-1)

[6](#coroutine.handle.con-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5950)

*Returns*: *this[.](#coroutine.handle.con-6.sentence-1)

#### [17.13.4.3](#coroutine.handle.conv) Conversion [[coroutine.handle.conv]](coroutine.handle.conv)

[🔗](#lib:operator_coroutine_handle%3c%3e,coroutine_handle)

`constexpr operator coroutine_handle<>() const noexcept;
`

[1](#coroutine.handle.conv-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5963)

*Effects*: Equivalent to: return coroutine_handle<>​::​from_address(address());

#### [17.13.4.4](#coroutine.handle.export.import) Export/import [[coroutine.handle.export.import]](coroutine.handle.export.import)

[🔗](#lib:address,coroutine_handle)

`constexpr void* address() const noexcept;
`

[1](#coroutine.handle.export.import-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5976)

*Returns*: ptr[.](#coroutine.handle.export.import-1.sentence-1)

[🔗](#lib:from_address,coroutine_handle)

`static constexpr coroutine_handle<> coroutine_handle<>::from_address(void* addr);
`

[2](#coroutine.handle.export.import-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5987)

*Preconditions*: addr was obtained via a prior call to address on an object whose type is a specialization of coroutine_handle[.](#coroutine.handle.export.import-2.sentence-1)

[3](#coroutine.handle.export.import-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L5992)

*Postconditions*: from_address(address()) == *this[.](#coroutine.handle.export.import-3.sentence-1)

[🔗](#lib:from_address,coroutine_handle_)

`static constexpr coroutine_handle<Promise> coroutine_handle<Promise>::from_address(void* addr);
`

[4](#coroutine.handle.export.import-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6003)

*Preconditions*: addr was obtained via a prior call to address on an object of type cv coroutine_handle<Promise>[.](#coroutine.handle.export.import-4.sentence-1)

[5](#coroutine.handle.export.import-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6008)

*Postconditions*: from_address(address()) == *this[.](#coroutine.handle.export.import-5.sentence-1)

#### [17.13.4.5](#coroutine.handle.observers) Observers [[coroutine.handle.observers]](coroutine.handle.observers)

[🔗](#lib:operator_bool,coroutine_handle)

`constexpr explicit operator bool() const noexcept;
`

[1](#coroutine.handle.observers-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6021)

*Returns*: address() != nullptr[.](#coroutine.handle.observers-1.sentence-1)

[🔗](#lib:done,coroutine_handle)

`bool done() const;
`

[2](#coroutine.handle.observers-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6032)

*Preconditions*: *this refers to a suspended coroutine[.](#coroutine.handle.observers-2.sentence-1)

[3](#coroutine.handle.observers-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6036)

*Returns*: true if the coroutine is suspended at its
final suspend point, otherwise false[.](#coroutine.handle.observers-3.sentence-1)

#### [17.13.4.6](#coroutine.handle.resumption) Resumption [[coroutine.handle.resumption]](coroutine.handle.resumption)

[1](#coroutine.handle.resumption-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6044)

Resuming a coroutine via resume, operator(), or destroy on an execution agent other than the one on which it was suspended
has implementation-defined behavior
unless
each execution agent either is
an instance of std​::​thread or std​::​jthread,
or is the thread that executes main[.](#coroutine.handle.resumption-1.sentence-1)

[*Note [1](#coroutine.handle.resumption-note-1)*:

A coroutine that is resumed on a different execution agent should
avoid relying on consistent thread identity throughout, such as holding
a mutex object across a suspend point[.](#coroutine.handle.resumption-1.sentence-2)

— *end note*]

[*Note [2](#coroutine.handle.resumption-note-2)*:

A concurrent resumption of the coroutine can result in a data race[.](#coroutine.handle.resumption-1.sentence-3)

— *end note*]

[🔗](#lib:operator(),coroutine_handle)

`void operator()() const;
void resume() const;
`

[2](#coroutine.handle.resumption-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6069)

*Preconditions*: *this refers to a suspended coroutine[.](#coroutine.handle.resumption-2.sentence-1)

The coroutine is not suspended at its final suspend point[.](#coroutine.handle.resumption-2.sentence-2)

[3](#coroutine.handle.resumption-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6074)

*Effects*: Resumes the execution of the coroutine[.](#coroutine.handle.resumption-3.sentence-1)

[🔗](#lib:destroy,coroutine_handle)

`void destroy() const;
`

[4](#coroutine.handle.resumption-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6085)

*Preconditions*: *this refers to a suspended coroutine[.](#coroutine.handle.resumption-4.sentence-1)

[5](#coroutine.handle.resumption-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6089)

*Effects*: Destroys the coroutine ([[dcl.fct.def.coroutine]](dcl.fct.def.coroutine "9.6.4 Coroutine definitions"))[.](#coroutine.handle.resumption-5.sentence-1)

#### [17.13.4.7](#coroutine.handle.promise) Promise access [[coroutine.handle.promise]](coroutine.handle.promise)

[🔗](#lib:promise,coroutine_handle)

`Promise& promise() const;
`

[1](#coroutine.handle.promise-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6102)

*Preconditions*: *this refers to a coroutine[.](#coroutine.handle.promise-1.sentence-1)

[2](#coroutine.handle.promise-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6106)

*Returns*: A reference to the promise of the coroutine[.](#coroutine.handle.promise-2.sentence-1)

#### [17.13.4.8](#coroutine.handle.compare) Comparison operators [[coroutine.handle.compare]](coroutine.handle.compare)

[🔗](#lib:operator==,coroutine_handle)

`constexpr bool operator==(coroutine_handle<> x, coroutine_handle<> y) noexcept;
`

[1](#coroutine.handle.compare-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6120)

*Returns*: x.address() == y.address()[.](#coroutine.handle.compare-1.sentence-1)

[🔗](#lib:operator%3c=%3e,coroutine_handle)

`constexpr strong_ordering operator<=>(coroutine_handle<> x, coroutine_handle<> y) noexcept;
`

[2](#coroutine.handle.compare-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6131)

*Returns*: compare_three_way()(x.address(), y.address())[.](#coroutine.handle.compare-2.sentence-1)

#### [17.13.4.9](#coroutine.handle.hash) Hash support [[coroutine.handle.hash]](coroutine.handle.hash)

[🔗](#lib:hash,coroutine_handle)

`template<class P> struct hash<coroutine_handle<P>>;
`

[1](#coroutine.handle.hash-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6144)

The specialization is enabled ([[unord.hash]](unord.hash "22.10.19 Class template hash"))[.](#coroutine.handle.hash-1.sentence-1)

### [17.13.5](#coroutine.noop) No-op coroutines [[coroutine.noop]](coroutine.noop)

#### [17.13.5.1](#coroutine.promise.noop) Class noop_coroutine_promise [[coroutine.promise.noop]](coroutine.promise.noop)

[🔗](#lib:noop_coroutine_promise)

`struct noop_coroutine_promise {};
`

[1](#coroutine.promise.noop-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6158)

The class noop_coroutine_promise defines the promise type for
the coroutine referred to
by noop_coroutine_handle ([[coroutine.syn]](#coroutine.syn "17.13.2 Header <coroutine> synopsis"))[.](#coroutine.promise.noop-1.sentence-1)

#### [17.13.5.2](#coroutine.handle.noop) Class coroutine_handle<noop_coroutine_promise> [[coroutine.handle.noop]](coroutine.handle.noop)

#### [17.13.5.2.1](#coroutine.handle.noop.general) General [[coroutine.handle.noop.general]](coroutine.handle.noop.general)

[🔗](#lib:coroutine_handle%3cnoop_coroutine_promise%3e)

namespace std {template<>struct coroutine_handle<noop_coroutine_promise>{// [[coroutine.handle.noop.conv]](#coroutine.handle.noop.conv "17.13.5.2.2 Conversion"), conversionconstexpr operator coroutine_handle<>() const noexcept; // [[coroutine.handle.noop.observers]](#coroutine.handle.noop.observers "17.13.5.2.3 Observers"), observersconstexpr explicit operator bool() const noexcept; constexpr bool done() const noexcept; // [[coroutine.handle.noop.resumption]](#coroutine.handle.noop.resumption "17.13.5.2.4 Resumption"), resumptionconstexpr void operator()() const noexcept; constexpr void resume() const noexcept; constexpr void destroy() const noexcept; // [[coroutine.handle.noop.promise]](#coroutine.handle.noop.promise "17.13.5.2.5 Promise access"), promise access noop_coroutine_promise& promise() const noexcept; // [[coroutine.handle.noop.address]](#coroutine.handle.noop.address "17.13.5.2.6 Address"), addressconstexpr void* address() const noexcept; private: coroutine_handle(*unspecified*); void* ptr; // *exposition only*};}

#### [17.13.5.2.2](#coroutine.handle.noop.conv) Conversion [[coroutine.handle.noop.conv]](coroutine.handle.noop.conv)

[🔗](#lib:operator_coroutine_handle%3c%3e,coroutine_handle%3cnoop_coroutine_promise%3e)

`constexpr operator coroutine_handle<>() const noexcept;
`

[1](#coroutine.handle.noop.conv-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6206)

*Effects*: Equivalent to: return coroutine_handle<>​::​from_address(address());

#### [17.13.5.2.3](#coroutine.handle.noop.observers) Observers [[coroutine.handle.noop.observers]](coroutine.handle.noop.observers)

[🔗](#lib:operator_bool,coroutine_handle%3cnoop_coroutine_promise%3e)

`constexpr explicit operator bool() const noexcept;
`

[1](#coroutine.handle.noop.observers-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6219)

*Returns*: true[.](#coroutine.handle.noop.observers-1.sentence-1)

[🔗](#lib:done,coroutine_handle%3cnoop_coroutine_promise%3e)

`constexpr bool done() const noexcept;
`

[2](#coroutine.handle.noop.observers-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6230)

*Returns*: false[.](#coroutine.handle.noop.observers-2.sentence-1)

#### [17.13.5.2.4](#coroutine.handle.noop.resumption) Resumption [[coroutine.handle.noop.resumption]](coroutine.handle.noop.resumption)

[🔗](#lib:operator(),coroutine_handle%3cnoop_coroutine_promise%3e)

`constexpr void operator()() const noexcept;
constexpr void resume() const noexcept;
constexpr void destroy() const noexcept;
`

[1](#coroutine.handle.noop.resumption-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6247)

*Effects*: None[.](#coroutine.handle.noop.resumption-1.sentence-1)

[2](#coroutine.handle.noop.resumption-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6251)

*Remarks*: If noop_coroutine_handle is converted to coroutine_handle<>,
calls to operator(), resume and destroy on that handle
will also have no observable effects[.](#coroutine.handle.noop.resumption-2.sentence-1)

#### [17.13.5.2.5](#coroutine.handle.noop.promise) Promise access [[coroutine.handle.noop.promise]](coroutine.handle.noop.promise)

[🔗](#lib:promise,coroutine_handle%3cnoop_coroutine_promise%3e)

`noop_coroutine_promise& promise() const noexcept;
`

[1](#coroutine.handle.noop.promise-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6266)

*Returns*: A reference to the promise object associated with this
coroutine handle[.](#coroutine.handle.noop.promise-1.sentence-1)

#### [17.13.5.2.6](#coroutine.handle.noop.address) Address [[coroutine.handle.noop.address]](coroutine.handle.noop.address)

[🔗](#lib:address,coroutine_handle%3cnoop_coroutine_promise%3e)

`constexpr void* address() const noexcept;
`

[1](#coroutine.handle.noop.address-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6280)

*Returns*: ptr[.](#coroutine.handle.noop.address-1.sentence-1)

[2](#coroutine.handle.noop.address-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6284)

*Remarks*: A noop_coroutine_handle's ptr is always a
non-null pointer value[.](#coroutine.handle.noop.address-2.sentence-1)

#### [17.13.5.3](#coroutine.noop.coroutine) Function noop_coroutine [[coroutine.noop.coroutine]](coroutine.noop.coroutine)

[🔗](#lib:noop_coroutine)

`noop_coroutine_handle noop_coroutine() noexcept;
`

[1](#coroutine.noop.coroutine-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6298)

*Returns*: A handle to a coroutine that has no observable effects
when resumed or destroyed[.](#coroutine.noop.coroutine-1.sentence-1)

[2](#coroutine.noop.coroutine-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6303)

*Remarks*: A handle returned from noop_coroutine may or may not
compare equal to a handle returned from another invocation
of noop_coroutine[.](#coroutine.noop.coroutine-2.sentence-1)

### [17.13.6](#coroutine.trivial.awaitables) Trivial awaitables [[coroutine.trivial.awaitables]](coroutine.trivial.awaitables)

[🔗](#lib:suspend_never)

namespace std {struct suspend_never {constexpr bool await_ready() const noexcept { return true; }constexpr void await_suspend(coroutine_handle<>) const noexcept {}constexpr void await_resume() const noexcept {}}; struct suspend_always {constexpr bool await_ready() const noexcept { return false; }constexpr void await_suspend(coroutine_handle<>) const noexcept {}constexpr void await_resume() const noexcept {}};}

[1](#coroutine.trivial.awaitables-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6335)

[*Note [1](#coroutine.trivial.awaitables-note-1)*:

The types suspend_never and suspend_always can be used
to indicate that an [*await-expression*](expr.await#nt:await-expression "7.6.2.4 Await [expr.await]") either never
suspends or always suspends, and in either case does not produce a value[.](#coroutine.trivial.awaitables-1.sentence-1)

— *end note*]