pw::async2::Coro< T > Class Template Reference

Overview

template<typename T>
class pw::async2::Coro< T >

An asynchronous coroutine which implements the C++20 coroutine API.

Why coroutines?

Coroutines allow a series of asynchronous operations to be written as straight line code. Rather than manually writing a state machine, users can co_await any pw_async2 future or another coroutine.

Allocation

Pigweed's Coro<T> API supports checked, fallible allocations with pw::Allocator. The first argument to any coroutine function must be a CoroContext&. This allows the coroutine to allocate space for asynchronously-held stack variables using the CoroContext's allocator.

Failure to allocate coroutine "stack" space will result in the Coro<T> returning Status::Invalid().

Creating a coroutine function

To create a coroutine, a function must:

• Have an annotated return type of Coro<T>, where T is the type that will be returned from within the coroutine.
• Use co_return <value> rather than return <value> for any return statements. For pw::Status or pw::Result, use PW_CO_TRY and PW_CO_TRY_ASSIGN rather than PW_TRY and PW_TRY_ASSIGN.
• Accept a CoroContext as its first argument. The CoroContext's allocator is used to allocate storage for coroutine stack variables held across a co_await point.

Using co_await

Inside a coroutine function, co_await <expr> can be used for pw_async2 futures or other coroutines. The result will be a value of type T.

Public Types
using	promise_type = ::pw::async2::internal::CoroPromise< T >
	Used by the compiler to create a Coro<T> from a coroutine function.
using	value_type = T
	The type this coroutine returns from a co_return expression.

Public Member Functions
bool	ok () const

Static Public Member Functions
static Coro	Empty ()
	Creates an empty, invalid coroutine object.

Friends
template<typename , typename >
class	internal::Awaitable
template<typename , ReturnValuePolicy >
class	CoroTask
template<typename , typename E , ReturnValuePolicy >
class	FallibleCoroTask

Member Function Documentation

ok()

template<typename T >

bool pw::async2::Coro< T >::ok ( ) const

inline

Whether or not this Coro<T> is a valid coroutine.

This will return false if coroutine state allocation failed or if this Coro<T>::Pend method previously returned a Ready value.

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The documentation for this class was generated from the following file:

• pw_async2/public/pw_async2/coro.h