twtg_11.9.5.go

// Suppose:

var ai AbsInterface // declares method Abs()
type SqrInterface interface { Sqr() float }
var si SqrInterface
pp := new(Point)  // say *Point implements Abs, Sqr
var empty interface{}


// Then the following statements and type assertions are valid:

empty = pp;  // everything satisfies empty
ai = empty.(AbsInterface);  // underlying value pp implements Abs()
                            // (runtime failure otherwise)
si = ai.(SqrInterface);  // *Point has Sqr() even though AbsInterface doesn’t
empty = si;  // *Point implements empty set
             // Note: statically checkable so type assertion not necessary.