mdznr/Swift Assertion Cheat Sheet.md

Last active February 16, 2022 23:31

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Compares the different behaviors of the various assertion functions in Swift

Raw

function	debug	release	release
Optimization Level	`-Onone`	`-O`	`-Ounchecked`
`assert()`	YES	NO	NO
`assertionFailure()`	YES	NO	NO^**
`precondition()`	YES	YES	NO
`preconditionFailure()`	YES	YES	YES^**
`fatalError()`^*	YES	YES	YES

Value	Meaning
YES	Terminates
NO	Does not terminate

^* Not really an assertion. It’s designed to terminate code execution always, no matter what.

^** The optimizer may assume that this function will never be called.

Sources:

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