Go语言爱好者周刊笔记-接口与反射关系

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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}