Add the EXACTLY_ONCE contract to suspendCancellableContinuation - #4574
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dkhalanskyjb merged 1 commit intoNov 25, 2025
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`suspendCancellableContinuation` invokes its block exactly once. `suspendCoroutineUninterceptedOrReturn`, which is used for implementing `suspendCancellableContinuation`, already has a contract stating just that, so for consistency and completeness, we add a contract to `suspendCancellableContinuation` itself as well. This will let the compiler recognize that `val`-variables can be safely assigned inside the lambda, as they won't be reassigned or left uninitialized (which would be the case if the lambda executed more than once or possibly not execute at all). There were no use cases actually reported for this.
murfel
approved these changes
Nov 25, 2025
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| /** Tests that the compiler recognizes that [suspendCancellableCoroutine] invokes its block exactly once. */ |
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by allowing the val variable
(the point of focus could be not immediately clear in future)
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Given that the whole test is five lines, there isn't a lot of room for misinterpreting what the test does, especially given that the KDoc describes that we're testing the EXACTLY_ONCE contract.
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| assertEquals(1, i) | ||
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| } No newline at end of file |
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Could you set your editor to add newlines?
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It's not at all straightforward, I'm afraid. Of course, I will make sure to do that if I learn that the lack of newlines in Kotlin files leads to some actual problems.
dkhalanskyjb
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November 25, 2025 13:02
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suspendCancellableContinuationinvokes its block exactly once.suspendCoroutineUninterceptedOrReturn,which is used for implementing
suspendCancellableContinuation, already has a contract stating just that,so for consistency and completeness, we add a contract to
suspendCancellableContinuationitself as well.This will let the compiler recognize that
val-variables can be safely assigned inside the lambda, as they won't be reassigned or left uninitialized (which would be the case if the lambda executed more than once or possibly not execute at all).There were no use cases actually reported for this.