Course of Raku / Functional, concurrent, reactive, and web programming / Reactive programming / await

Waiting for completion

await is the explicit way to wait, but reactive code waits too — just implicitly. A react block does not finish until all the supplies it watches are done, which gives you the same “everything has completed” guarantee:

my @values;

react {
    whenever Supply.from-list(2, 4, 6) {
        @values.push($_);
    }
}

say [+] @values; # 12

The say runs only after the react block has finished, so @values already holds every emitted value. In effect, the react block awaited the stream for you.

This is a useful pattern: use a react block to collect everything a supply emits, and then work with the collected result on the line after, confident that the stream is complete. Whether you wait for a promise with await or for a stream with react, the principle is the same — pause until the concurrent work is done, then continue with its results.

← Quiz — await | Await a promise →

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Waiting for completion

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