Things I Love About Go(cambus.net)

    type Fruit struct {
        Name    string
        Species string
    }

    // define a method on Fruit structs named Rename
    func (f *Fruit) Rename(s string) {
        f.Name = s
    }

    type Candy struct {
        Name    string
        Company string
    }

    // define a method on Candy structs named Rename
    func (c *Candy) Rename(s string) {
        c.Name = s
    }

    // any type that defines a method named Rename is also 
    // of type Renamable.
    type Renamable interface {
        Rename(string)
    }

    // produce something that implements Renamable.  Its   
    // fields will be unknown, but the method Rename will be 
    // known to exist.
    func SomeProducer(...) Renamable {
        ...
    }

    x := SomeProducer(...)
    // at this point, x is of type Renamable.  We do not 
    // know what fields it has.  The only thing we know is 
    // that it has some method named Rename that takes a 
    // single string for its only argument and returns 
    // nothing.

    switch t := x.(type) {
    case Fruit:
        // T is of type Fruit, while x is of type Renamable
        fmt.Print(t.Species)
    case Candy:
        // T is of type Candy, while x is of type Renamable
        fmt.Print(t.Company)
    default:
        // some other type.
    }