golang无法解析json以创建反射对象

 interface {}  interface {} 

 包主
 
 importfmt
 
 func main（）{
 var m1 struct {Data string} 
 var m2 interface {} 
 var m3 interface {} 
 
 m2 =& m1 
 m3 = m1 
 
 fmt.Printf（& m1 =％p m2 =％p& m3 =％p \ n，& m1，m2，&m3）
} 
  

，在上面的例子中使用零等于m3。使用New等于m2。

I try to write simple message protocol in go and i've encountered a problem. I have a lot of message types and i want to have a dictionary like this to manipulate with messages:

var dict map[reflect.Type]int = map[reflect.Type]int{
    reflect.TypeOf(DataMessage{}):          1000,
    reflect.TypeOf(TextMessage{}):          1001,
    //....
}

func GetMessageTypeId(value interface{}) int {
    if id, ok := dict[reflect.TypeOf(value)]; ok {
        return id
    } else {
        return -1
    }
}

func GetValueByTypeId(typeId int) interface{} {
    for typeDec, id := range dict {
        if id == typeId {
            return reflect.Zero(typeDec).Interface()
        }
    }
    fmt.Println("Unknown message type", typeId)
    return nil
}

It works fine, but when i instantiate message with GetValueByTypeId and try to unmarshall json into it - i receive map[string]interface instead of my message. I've made simple example to reproduce the problem:

Please read this article: http://research.swtch.com/interfaces, especially the "Memory Optimizations".

The interface{} by definition consists of two pointers - to method table (e.g. type) and to data it holds. So for

var destination3 interface{} = reflect.Zero(reflect.TypeOf(Message{})).Interface()

interface{}Message{}interface{}

interface{}interface{}

package main

import "fmt"

func main() {
    var m1 struct{ Data string }
    var m2 interface{}
    var m3 interface{}

    m2 = &m1
    m3 = m1

    fmt.Printf("&m1=%p m2=%p &m3=%p\n", &m1, m2, &m3)
}

In your case, using Zero is equivalent to m3 in the example above. Using New is equivalent to m2.

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