errors

func As ¶

func As(err error, target any) bool

As finds the first error in err's tree that matches target, and if one is found, sets target to that error value and returns true. Otherwise, it returns false.

The tree consists of err itself, followed by the errors obtained by repeatedly calling its Unwrap() error or Unwrap() []error method. When err wraps multiple errors, As examines err followed by a depth-first traversal of its children.

An error matches target if the error's concrete value is assignable to the value pointed to by target, or if the error has a method As(any) bool such that As(target) returns true. In the latter case, the As method is responsible for setting target.

An error type might provide an As method so it can be treated as if it were a different error type.

As panics if target is not a non-nil pointer to either a type that implements error, or to any interface type.

func Code ¶

func Code(err error) int

func Errorf ¶

func Errorf(code int, reason, format string, a ...any) error

func Is ¶

func Is(err, target error) bool

Is reports whether any error in err's tree matches target.

The tree consists of err itself, followed by the errors obtained by repeatedly calling its Unwrap() error or Unwrap() []error method. When err wraps multiple errors, Is examines err followed by a depth-first traversal of its children.

An error is considered to match a target if it is equal to that target or if it implements a method Is(error) bool such that Is(target) returns true.

An error type might provide an Is method so it can be treated as equivalent to an existing error. For example, if MyError defines

func (m MyError) Is(target error) bool { return target == fs.ErrExist }

then Is(MyError{}, fs.ErrExist) returns true. See syscall.Errno.Is for an example in the standard library. An Is method should only shallowly compare err and the target and not call Unwrap on either.

func Reason ¶

func Reason(err error) string

func Unwrap ¶

func Unwrap(err error) error

Unwrap returns the result of calling the Unwrap method on err, if err's type contains an Unwrap method returning error. Otherwise, Unwrap returns nil.

Unwrap only calls a method of the form "Unwrap() error". In particular Unwrap does not unwrap errors returned by [Join].