38-interface-methodset.go

package _interface

import (
	"fmt"
)

type Appender interface {
	Append(int)
}
type Lener interface {
	Len() int
}

//list类型实现了Appender和Lener接口
type List []int

func (l List) Len() int {
	return len(l)
}

func (l *List) Append(val int) {
	*l = append(*l, val)
}

func CountInto(a Appender, start, end int) {
	for i := start; i <= end; i++ {
		a.Append(i)
	}
}
func LongEnough(l Lener) bool {
	return l.Len()*10 > 42
}

func main() {
	// A bare value
	var lst List
	// compiler error:
	// cannot use lst (type List) as type Appender in argument to CountInto:
	//       List does not implement Appender (Append method has pointer receiver)
	//CountInto(lst, 1, 10)
	if LongEnough(lst) { // VALID:Identical receiver type
		fmt.Printf("- lst is long enough\n")
	}

	// A pointer value
	plst := new(List)
	CountInto(plst, 1, 10) //VALID:Identical receiver type
	if LongEnough(plst) {
		// VALID: a *List can be dereferenced for the receiver
		fmt.Printf("- plst is long enough\n")
	}
}