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package main
import (
"fmt"
"time"
)
type MyWriter interface {
Write(p []byte) (i int, err error)
}
type DummyWriter interface {
Write(p []byte) (i int, err error)
}
type TestStruct struct{}
func (t TestStruct) Write(p []byte) (n int, err error) {
return len(p), nil
}
func usesWriter(w MyWriter) {
n, _ := w.Write([]byte("hello world"))
fmt.Println(n)
}
type MyStringer interface {
String() string
}
type DummyStringer interface {
String() string
}
func usesStringer(s MyStringer) {
fmt.Println(s.String())
}
func main() {
// TODO(mpl): restore when we can deal with empty interface.
// var t interface{}
var t DummyWriter
t = TestStruct{}
var tw MyWriter
var ok bool
tw, ok = t.(MyWriter)
if !ok {
fmt.Println("TestStruct does not implement MyWriter")
} else {
fmt.Println("TestStruct implements MyWriter")
usesWriter(tw)
}
n, _ := t.(MyWriter).Write([]byte("hello world"))
fmt.Println(n)
// not redundant with the above, because it goes through a slightly different code path.
if _, ok := t.(MyWriter); !ok {
fmt.Println("TestStruct does not implement MyWriter")
return
} else {
fmt.Println("TestStruct implements MyWriter")
}
// TODO(mpl): restore
/*
t = 42
foo, ok := t.(MyWriter)
if !ok {
fmt.Println("42 does not implement MyWriter")
} else {
fmt.Println("42 implements MyWriter")
}
_ = foo
if _, ok := t.(MyWriter); !ok {
fmt.Println("42 does not implement MyWriter")
} else {
fmt.Println("42 implements MyWriter")
}
*/
// var tt interface{}
var tt DummyStringer
tt = time.Nanosecond
var myD MyStringer
myD, ok = tt.(MyStringer)
if !ok {
fmt.Println("time.Nanosecond does not implement MyStringer")
} else {
fmt.Println("time.Nanosecond implements MyStringer")
usesStringer(myD)
}
fmt.Println(tt.(MyStringer).String())
if _, ok := tt.(MyStringer); !ok {
fmt.Println("time.Nanosecond does not implement MyStringer")
} else {
fmt.Println("time.Nanosecond implements MyStringer")
}
// TODO(mpl): restore
/*
tt = 42
bar, ok := tt.(MyStringer)
if !ok {
fmt.Println("42 does not implement MyStringer")
} else {
fmt.Println("42 implements MyStringer")
}
_ = bar
if _, ok := tt.(MyStringer); !ok {
fmt.Println("42 does not implement MyStringer")
} else {
fmt.Println("42 implements MyStringer")
}
*/
}
// Output:
// TestStruct implements MyWriter
// 11
// 11
// TestStruct implements MyWriter
// time.Nanosecond implements MyStringer
// 1ns
// 1ns
// time.Nanosecond implements MyStringer
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