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接口是抽象基本工具
接口在分配值时候存储类型信息，反射在运行时检查类型和值方法
像一个接接口分配一个值
一个接口编码三件事 ：值，方法集，以及所存储值类型
image
接口内部结构三个部分：_type类型信息,*data指向实际值指针,itab是方法集.
方法接受接口作为参数,值传递给函数则会将该值,值方法集,类型打包到接口中
通过反射包运行时检查接口
一个值存储进接口,reflect检查接口各部分.不能直接检查接口结构而是反射包维护有权访问的接口结构副本
reflect.Type和reflect.Vallue
.type 侧重于公开类型相关数据因此只限于_type部分,
.value则必须将类型信息与值结合起来以检查和操作值.因此必须查看_type和*data部分
.type检查类型
.typeof()用于从一个值中提取值类型信息,该函数唯一的参数是一个空接口interface(),传递的值付到空接口,因此该值类型方法集合都可以轻松获得.
.typeof返回.type类型值有类型.type.size();.type.kind();.type.name();.type.filed()
.type.numfiled()得到结构中参数数目,.type.field(n).type.kind();
.method检查itab方法集(结构体所有实现方法)
.type.method(0);.type.methodbyname("name");.type.Nummethod()
t.nummethod()
.value()展示实际存储在接口中的信息
相关方法必须将类型信息和实际值结合在一起,为了从一个结构中提取字段信息,refelect包必须将结构布局只是,存储在_type中字段和字段偏移量信息与接口*data部分所指实际值结合起来解码
.value.kind .vallue.field()+.value.pointer()结合找到运行时状态
1package main
2
3import (
4 "log"
5 "reflect"
6)
7
8type Child struct {
9 Name string
10 Grade int
11 Nice bool
12}
13
14type Adult struct {
15 Name string
16 Occupation string
17 Nice bool
18}
19
20// search a slice of structs for Name field that is "Hank" and set its Nice
21// field to true.
22func nice(i interface{}) {
23 // retrieve the underlying value of i. we know that i is an
24 // interface.
25 v := reflect.ValueOf(i)
26
27 // we're only interested in slices to let's check what kind of value v is. if
28 // it isn't a slice, return immediately.
29 if v.Kind() != reflect.Slice {
30 return
31 }
32
33 // v is a slice. now let's ensure that it is a slice of structs. if not,
34 // return immediately.
35 if e := v.Type().Elem(); e.Kind() != reflect.Struct {
36 return
37 }
38
39 // determine if our struct has a Name field of type string and a Nice field
40 // of type bool
41 st := v.Type().Elem()
42
43 if nameField, found := st.FieldByName("Name"); found == false || nameField.Type.Kind() != reflect.String {
44 return
45 }
46
47 if niceField, found := st.FieldByName("Nice"); found == false || niceField.Type.Kind() != reflect.Bool {
48 return
49 }
50
51 // Set any Nice fields to true where the Name is "Hank"
52 for i := 0; i < v.Len(); i++ {
53 e := v.Index(i)
54 name := e.FieldByName("Name")
55 nice := e.FieldByName("Nice")
56
57 if name.String() == "Hank" {
58 nice.SetBool(true)
59 }
60 }
61}
62
63func main() {
64 children := []Child{
65 {Name: "Sue", Grade: 1, Nice: true},
66 {Name: "Ava", Grade: 3, Nice: true},
67 {Name: "Hank", Grade: 6, Nice: false},
68 {Name: "Nancy", Grade: 5, Nice: true},
69 }
70
71 adults := []Adult{
72 {Name: "Bob", Occupation: "Carpenter", Nice: true},
73 {Name: "Steve", Occupation: "Clerk", Nice: true},
74 {Name: "Nikki", Occupation: "Rad Tech", Nice: false},
75 {Name: "Hank", Occupation: "Go Programmer", Nice: false},
76 }
77
78 log.Printf("adults before nice: %v", adults)
79 nice(adults)
80 log.Printf("adults after nice: %v", adults)
81
82 log.Printf("children before nice: %v", children)
83 nice(children)
84 log.Printf("children after nice: %v", children)
85}
