golang(* interface {})(nil)是否为零？

发布时间：2020-12-16 19:03:11 所属栏目：大数据来源：网络整理

导读：代码段如下： package mainimport ( "fmt" "reflect")func main() { a := (*interface{})(nil) fmt.Println(reflect.TypeOf(a),reflect.ValueOf(a)) var b interface{} = (*interface{})(nil) fmt.Println(reflect.TypeOf(b),reflect.ValueOf(b)) fmt.Printl

代码段如下：

package main

import (
    "fmt"
    "reflect"
)

func main() {
    a := (*interface{})(nil)
    fmt.Println(reflect.TypeOf(a),reflect.ValueOf(a))
    var b interface{} = (*interface{})(nil)
    fmt.Println(reflect.TypeOf(b),reflect.ValueOf(b))
    fmt.Println(a == nil,b == nil)
}

输出如下：

*interface {} <nil>
*interface {} <nil>
true false

所以var interface {}不同于：=,为什么？

根据 golang faq

Under the covers,interfaces are implemented as two elements,a type and a value. The value,called the interface’s dynamic value,is an arbitrary concrete value and the type is that of the value. For the int value 3,an interface value contains,schematically,(int,3).

An interface value is nil only if the inner value and type are both unset,(nil,nil). In particular,a nil interface will always hold a nil type. If we store a nil pointer of type *int inside an interface value,the inner type will be *int regardless of the value of the pointer: (*int,nil). Such an interface value will therefore be non-nil even when the pointer inside is nil.

a：=(* interface {})(nil)等于var a * interface {} = nil.

但是var b interface {} =(* interface {})(nil),mean b是type interface {},而interface {}变量只有nil,当它的类型和值都是nil时,显然type * interface {}不是nil .

（编辑：李大同）

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