Document EventLoopFuture callback lifetimes - #3701
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Motivation: Developers coming from UIKit often capture self weakly in Future callbacks to avoid retain cycles. For EventLoopFuture that pattern is unnecessary: callbacks run at most once and are then dropped, and dropping an EventLoopPromise without completing it is programmer error. Modifications: Add a Callback lifetimes section to the EventLoopFuture type docs, and note on EventLoopPromise that completing a promise is required. Result: The docs discourage weak and unowned captures in Future callbacks and explain why a strong capture of self is the correct default.
Lukasa
enabled auto-merge (squash)
August 13, 2026 12:16
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Summary
Developers coming from UIKit often capture self weakly in Future callbacks to avoid retain cycles. EventLoopFuture callbacks run at most once and are then dropped. Dropping an EventLoopPromise without completing it is programmer error. Together those rules mean a strong capture of self is the correct default.
This adds a Callback lifetimes section to the EventLoopFuture type docs and notes the completion requirement on EventLoopPromise.
Fixes #1575
Test plan
This change is documentation only. I reviewed the new section against the existing Callbacks threading notes on EventLoopFuture.