Using functions in Go declarations

funcvars.md

Using functions in Go declarations

The best way to approach the limitations of Go's type system in regards to the function signature and closures, is to simply use variables. This also gives you something you can set to nil to become a typed nil, which is quite nasty syntax also.

var DefaultHandler = func(s string) error {
  return nil
}

then you can use this:

var ConfigTree = Config{
  Name: "somename",
  Handler: DefaultHandler,
}

func main() {
  if err := ConfigTree.Handler("testing"); err != nil {
    panic(err)
  }
  ConfigTree = nil
  if ConfigTree != nil {
    panic("this cannot happen") // expect linter to say so
  }
}

This lets you DRY out some of your Go code :)