expose Unmarshaler interface

[sGy1980de]

Hey guys,

I was wondering why there seems to be no interface for the Unmarshaler type.
Turns out there is one, but it's hidden in the internal scope.

This makes it impossible to have an assertion, whether my own type implements it properly or not.
So is there a particular reason, why it is internal or is it by mistake?

[maoueh]

@sGy1980de As a workaround, you can always define the same interface in your own code and test against, this works also in Go, you don't need to check against the actual defined interface. Here and example that tests fmt.Stringer interface, using a custom defined one:

type S1 struct {
	value string
}

func (s *S1) String() string {
	return s.value
}

type myStringer interface {
	String() string
}

func main() {
	s1 := &S1{}
	var v interface{} = s1

	_, isStringer := v.(fmt.Stringer)
	_, isMyStringer := v.(myStringer)

	fmt.Println("Answers", isStringer, isMyStringer)
}

# Prints
# Answers true true

See https://play.golang.org/p/4_jwJ9OJtu6

You can use it to make your check on your side.