Why it matters

Futures replace callback pyramids with linear-looking code. Understanding them is essential for modern async programming.

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The architecture

Future: read-only value. Completion states: pending, completed with value, completed with error.

Promise: writable side. set_value or set_error completes the future.

Future/Promise modelPromiseproducerFutureconsumerCallbacks / awaitprocess on completeasync/await syntax makes futures look like sync code; standard modern async pattern
Future + Promise pair.
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How it works end to end

Composition: chain futures with then/map/flatMap. Errors propagate through chains.

async/await: syntactic sugar over futures. Makes code linear.

All/Any combinators: wait for multiple futures.