Overview

Errors are values in Go!

Errors

• Most of the funcs in the standard library return 2 values. One is the expected value of expected type, the other is error.
• error is an interface defined in the builtin package
  • type error interface { Error() string }
  • Any type which has a Error() string receiver, implements it
• Standard library has some concrete implementations of error interface. Like:
  • *fs.PathError
  • *strconv.NumError
• package errors
  • errors.New(<message>)
    • it makes it easy to create errors on the fly

Russian doll of errors

• With Go 1.13, you can define custom errors which wrap other errors like a Matryoshka...

• errors package has 2 new methods:

  • As finds the first error in err's chain that matches target
  • Is reports whether any error in err's chain matches target

• All you need to do, in order for standard library to work with such an implementation of error is to implement Unwrap() error method on your custom error type