go/test/interface/convert.go

// $G $D/$F.go && $L $F.$A && ./$A.out

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Check uses of all the different interface
// conversion runtime functions.

package main

type Stringer interface { String() string }
type StringLengther interface { String() string; Length() int }
type Empty interface { }

type T string
func (t T) String() string {
	return string(t);
}
func (t T) Length() int {
	return len(t);
}

type U string
func (u U) String() string {
	return string(u);
}

var t = T("hello")
var u = U("goodbye")
var e Empty
var s Stringer = t
var sl StringLengther = t
var i int
var ok bool

func hello(s string) {
	if s != "hello" {
		panic("not hello: ", s);
	}
}

func five(i int) {
	if i != 5 {
		panic("not 5: ", i);
	}
}

func true(ok bool) {
	if !ok {
		panic("not true");
	}
}

func false(ok bool) {
	if ok {
		panic("not false");
	}
}

func main() {
	// T2I
	s = t;
	hello(s.String());

	// I2T
	t = s.(T);
	hello(t.String());

	// T2E
	e = t;

	// E2T
	t = e.(T);
	hello(t.String());

	// T2I again
	sl = t;
	hello(sl.String());
	five(sl.Length());

	// I2I static
	s = sl;
	hello(s.String());

	// I2I dynamic
	sl = s.(StringLengther);
	hello(sl.String());
	five(sl.Length());

	// I2E (and E2T)
	e = s;
	hello(e.(T).String());

	// E2I
	s = e.(Stringer);
	hello(s.String());

	// I2T2 true
	t, ok = s.(T);
	true(ok);
	hello(t.String());

	// I2T2 false
	var u1 U;
	u1, ok = s.(U);
	false(ok);

	// I2I2 true
	sl, ok = s.(StringLengther);
	true(ok);
	hello(sl.String());
	five(sl.Length());

	// I2I2 false (and T2I)
	s = u;
	sl, ok = s.(StringLengther);
	false(ok);

	// E2T2 true
	t, ok = e.(T);
	true(ok);
	hello(t.String());

	// E2T2 false
	i, ok = e.(int);
	false(ok);

	// E2I2 true
	sl, ok = e.(StringLengther);
	true(ok);
	hello(sl.String());
	five(sl.Length());

	// E2I2 false (and T2E)
	e = u;
	sl, ok = e.(StringLengther);
	false(ok);
}