beman.lazy: Beman Library Implementation of lazy (P3552)

beman::execution::lazy<T, Context> is a class template which is used as the the type of coroutine tasks. The corresponding objects are senders. The first template argument (T) defines the result type which becomes a set_value_t(T) completion signatures. The second template argument (Context) provides a way to configure the behavior of the coroutine. By default it can be left alone.

Implements: std::execution::lazy proposed in Add a Coroutine Lazy Type (P3552r0).

Usage

The following code snippet shows a basic use of beman::lazy::lazy using sender/receiver facilities to implement version of hello, world:

#include <beman/lazy/lazy.hpp>
#include <beman/execution/execution.hpp>
#include <iostream>

namespace ex = beman::execution;
namespace ly = beman::lazy;

int main() {
    return std::get<0>(*ex::sync_wait([]->ex::lazy<int> {
        std::cout << "Hello, world!\n";
        co_return co_await ex::just(0);
    }()));
}

Full runnable examples can be found in examples/ (e.g., ./examples/hello.cpp).

Help Welcome

There are plenty of things which need to be done. See the contributions page for some ideas how to contribute. The resources page contains some links for general information about coroutines.

Building beman.lazy

Dependencies

This project depends on beman::execution (which will be automatically obtained using cmake's FetchContent*).

Build-time dependencies:

• cmake
• ninja, make, or another CMake-supported build system
  • CMake defaults to "Unix Makefiles" on POSIX systems

How to build beman.lazy

This project strives to be as normal and simple a CMake project as possible. This build workflow in particular will work, producing a static libbeman.lazy.a library, ready to package with its headers:

cmake --workflow --preset gcc-debug
cmake --workflow --preset gcc-release
cmake --install build/gcc-release --prefix /opt/beman.lazy

Contributing

Please do! Issues and pull requests are appreciated.