Custom Map function

[Gabriel Nelle]

Similar to the json.Marshal() it would be really great to have the ability to add my own Map() function to a struct in order to overwrite the default mapping.

Example use case:

type foo struct {
	data bar
}

type bar struct {
	Name  string
	Value string
}

func main() {
	f := &foo{
		data: bar{
			Name:  "foo",
			Value: "bar",
		},
	}
	fmt.Println(structs.Map(f))
}

In this example the actual data is hidden away and only accessible from the foo struct itself (at least outside the package). So I would want to build a function foo.Map() that can extract the data. In a nested case it is necessary that the map package calls the custom Map function if it exists.

[Gabriel Nelle]

see #101