Provides a select_loop! macro allowing to loop awaiting for multiple streams and/or futures, and is aimed to be used instead of using tokio's select! macro inside a loop, which may cause issues with cancelation safety.

Select loops are a nice design pattern to write async tasks continuously awaiting for events/messages while managing an internal state without mutexes, since only one event/message is processed at a time.

The body of the select_loop! macro looks like a match statement with additional syntax.

• F my_future => |item| ..., allows to await for a Future. Once the Future resolves the branch is executed.
• S my_stream => |item| ..., allows to await for a Stream. Each time the Stream outputs an item the branch is executed.

The macro takes ownership of the Future/Stream and requires it to be Unpin.

Additionally it is possible to hook on various stages of the select loop:

• @before => ... is executed just before any branch is executed, but after one of the futures or stream has outputed an item.
• @after => ... is executed just after any branch is executed.
• @exhausted => ... is executed when all futures and streams are exhausted. The value returned by the last @exhausted branch is returned by the select_loop! (it corresponds to a break ...; inside the macro expansion).

As the macro expands into a Rust loop, break and continue can be used like with normal loops. break followed by a value can even be used as long as all break return values of the same type, and that at least one @exhausted branch exists and the last one returns a value of the same type. If you have multiple nested loops, you can refer to the select loop using the 'select_loop lifetime.

Examples are available here