extend-classes.go

package main

// Existing classes we can't extend because they are
// in a different package.
type Foo struct {
	Name string
}

type Bar struct {
	Name string
}

type Baz struct {
	Name string
}

// These new types are introduced so we can add
// methods too Foo, Bar, and Baz.
type MyFoo Foo
type MyBar Bar
type MyBaz Baz

// Add the new method to the new type so it implements Named.
func (foo *MyFoo) GetName() string {
	return foo.Name
}

// Add the new method to the new type so it implements Named.
func (bar *MyBar) GetName() string {
	return bar.Name
}

// Add the new method to the new type so it implements Named.
func (baz *MyBaz) GetName() string {
	return baz.Name
}

// Implemented by the new type.
type Named interface {
	GetName() string
}

func main() {
	var slice []Named
	// We have to wrap the old types in the new ones.  This takes
	// a copy of the struct.
	my_foo := MyFoo(Foo{Name: "fooname"})
	my_bar := MyBar(Bar{Name: "barname"})
	my_baz := MyBaz(Baz{Name: "bazname"})
	// Because they are wrapped, they implement the new
	// interface.
	slice = append(slice, &my_foo)
	slice = append(slice, &my_bar)
	slice = append(slice, &my_baz)
	for _, named := range slice {
		println(named.GetName())
	}
}