===== error interface =====

==== What is it? ====
`error` is a built-in interface type in Go:

<code go>
type error interface {
    Error() string
}
</code>

Any type that implements `Error() string` can be used as an error.

==== What is it used for? ====
  * Standardize how functions return failure information.
  * Allow custom error types while still matching `error`.

==== Example ====
<code go>
type MyError struct{ Msg string }

func (e MyError) Error() string { return e.Msg }

func f() error {
    return MyError{Msg: "something went wrong"}
}
</code>

==== Notes ====
  * `nil` error means success.
  * Be careful: an interface can be non-nil even if it holds a typed nil (advanced pitfall).

==== Hard words (English) ====
  * **interface** /ˈɪntərfeɪs/: giao diện
  * **implement** /ˈɪmplɪment/: triển khai
  * **pitfall** /ˈpɪtfɔːl/: bẫy thường gặp