golang 中的 nil的场景分析

// nil is a predeclared identifier representing the zero value for a
// pointer, channel, func, interface, map, or slice type.
var nil Type // Type must be a pointer, channel, func, interface, map, or slice type

func t1() {
 var i interface{}
 var p *int

 fmt.Println("p==i", p == i)
 fmt.Println("i=", i, "i==null", i == nil)
 fmt.Println("p=", p, "p==nil", p == nil)
 fmt.Println("i TypeOf=", reflect.TypeOf(i), "i ValueOf", reflect.ValueOf(i))
 fmt.Println("p TypeOf=", reflect.TypeOf(p), "p ValueOf", reflect.ValueOf(p))
 i = p
 fmt.Println("---")
 fmt.Println("p==i", p == i)
 fmt.Println("i=", i, "i==null", i == nil)
 fmt.Println("p=", p, "p==nil", p == nil)
 fmt.Println("i TypeOf=", reflect.TypeOf(i), "i ValueOf", reflect.ValueOf(i))
 fmt.Println("p TypeOf=", reflect.TypeOf(p), "p ValueOf", reflect.ValueOf(p))

}

func t3() {
 f1 := func(i interface{}) bool {
  return i == nil
 }

 var a *int
 fmt.Println(f1(a)) // false
 fmt.Println(f1(nil)) // true
}

type A struct {
}

func (A) a1() int {
 return 123
}

func (*A) a2() int {
 return 321
}

type B interface {
}

func t2() {
 var a A
 var ap *A
 var b B
 var bp *B

 fmt.Println("a=", a, "a.a1()", a.a1(), a.a2()) //a= {} a.a1() 123 321; a == nil 会抛错 struct 不能和 nil 进行比较
 fmt.Println("ap=", ap, "ap==nil", ap == nil) //ap= <nil> ap==nil true

 fmt.Println("b=", b, " b==nil：", b == nil)  // b= <nil> b==nil： true
 fmt.Println("bp=", bp, " bp==nil：", bp == nil) //bp= <nil> bp==nil： true
}