errors

Documentation

Index

• func As(err error, target interface{}) bool
• func Cause(err error) error
• func Errorf(format string, a ...interface{}) error
• func Is(err, target error) bool
• func Merge(err ...error) error
• func New(text string) error
• func Unwrap(err error) error
• func Wrapf(err error, format string, a ...interface{}) error

Functions

func As

func As(err error, target interface{}) bool

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

The chain consists of err itself followed by the sequence of errors obtained by repeatedly calling Unwrap.

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(interface{}) 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 Cause

func Cause(err error) error

Cause returns the underlying cause for this error, if possible. If err does not implement causer.Cause(), then err is returned.

Deprecated: Use errors.Unwrap, errors.Is or errors.As instead.

func Errorf

func Errorf(format string, a ...interface{}) error

Errorf formats according to a format specifier and returns the string as a value that satisfies error.

If the format specifier includes a %w verb with an error operand, the returned error will implement an Unwrap method returning the operand. It is invalid to include more than one %w verb or to supply it with an operand that does not implement the error interface. The %w verb is otherwise a synonym for %v.

func Is

func Is(err, target error) bool

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

The chain consists of err itself followed by the sequence of errors obtained by repeatedly calling Unwrap.

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 == os.ErrExist }

then Is(MyError{}, os.ErrExist) returns true. See syscall.Errno.Is for an example in the standard library.

func Merge

func Merge(err ...error) error

Merge errors into one, nil errors are discarded and returns nil if all errors are nil.

func New

func New(text string) error

New returns an error that formats as the given text. Each call to New returns a distinct error value even if the text is identical.

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.

func Wrapf

func Wrapf(err error, format string, a ...interface{}) error

Wrapf wraps an error with a message. Wrapf returns nil if error is nil.