XO0205: `?` where the enclosing function cannot return the failure

error · reported by the checker

? on a Result needs a function or closure that can fail, and ? on an optional needs one that returns an optional. A function without ! cannot propagate an error, and a requires ... else clause in such a function has nowhere to return its error either. Declare the error type (the diagnostic offers ! E as a fix), or handle the failure with match, ??, or ignore_err. See core 2.5 and 2.6.

Example

enum E { A }

fn g() -> Int ! E { 1 }

fn f() -> Int { g()? }

Fix

enum E { A }

fn g() -> Int ! E { 1 }

fn f() -> Int ! E { g()? }

Run xo explain XO0205 for this text in a terminal, or see section 10.6 of the specification.

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Reference

XO0205: `?` where the enclosing function cannot return the failure

Example

Fix