Checks a dispatch condition necessary for further execution.


func dispatchPrecondition(condition: @autoclosure () -> DispatchPredicate)



A dispatch predicate for the current context to check.


Use this function to detect conditions about the current execution context that must prevent the program from proceeding even in shipping code.

  • In playgrounds and -Onone builds (the default for Xcode’s Debug configuration): if condition evaluates to false, stop program execution in a debuggable state.

  • In -O builds (the default for Xcode’s Release configuration): if condition evaluates to false, stop program execution.

  • In -Ounchecked builds, condition is not evaluated, but the optimizer may assume that it would evaluate to true. Failure to satisfy that assumption in -Ounchecked builds is a serious programming error.

See Also

Dispatch Objects

class DispatchObject

The base class for most dispatch types.

enum DispatchPredicate

Logical conditions to evaluate within a given execution context.

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