cobalt

Boost.Cobalt is a C++ library that gives developers tools for writing asynchronous code that reads like normal, top-to-bottom code. Normally, when a program needs to wait for something like a network response or a timer, it either blocks completely or forces the developer to use callbacks, which tangle the logic. This library uses coroutines to let the code wait for operations without freezing the whole application and without scattering logic across callback functions.

At a high level, the library provides building blocks like promises, tasks, generators, and channels. A promise starts running immediately, while a task waits until explicitly activated. Generators produce a series of values over time. Channels work like those in Go, allowing different parts of a program to pass messages to each other safely. The library also includes utilities like race, which lets a program wait for multiple operations at once and proceed when the first one finishes.

This is useful for developers building applications that handle heavy input and output, such as network servers or programs managing many simultaneous connections. For example, a server handling hundreds of client connections can use these tools to manage timers and communications cleanly. Instead of deeply nested callback functions, the developer writes straightforward code that waits for a response, processes it, and moves to the next step.

The library runs on top of Boost.Asio, a well-established C++ networking library, and requires a relatively modern version of C++ that supports coroutines. It provides a main entry point that handles setup, including forwarding interruption signals so the program can shut down gracefully. Notably, the repository uses Zig's build system for its testing, though the library itself is written entirely in C++.