golang无法解析json以创建反射对象 [英] golang fails to parse json for reflection created object
问题描述
我尝试编写简单的消息协议,并且遇到了问题。我有很多消息类型,我想要这样的字典来处理消息:
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(未知消息类型,typeId)
返回零
}
它工作正常,但是当我使用GetValueByTypeId实例化消息并尝试解组json时 - 我收到map [string]接口而不是我的消息。
我做了一个简单的例子来重现问题:
http://play.golang.org/p/QEyDN9vztr
请阅读文章: http://research.swtch.com/interfaces ,特别是内存优化。 p>
定义中的接口{}由两个指针组成 - 包括方法表(例如类型)和它所保存的数据。因此,对于
var destination3接口{} = reflect.Zero(reflect.TypeOf(Message {}))。 b $ b
它是空的方法表(如 interface {}
没有方法)并引用 Message {}
。通过引用它可以返回对此结构的引用,所以unmarhal用任何匹配 interface {}
覆盖它。
如果数据 interface {}
变量持有本身就是一个指针,那么它会以使用该指针的方式进行优化,而不是创建 interface {}
结构。因此,引用它可以引用原始变量。
http://play.golang.org/p/KsIS29rUAX
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:
http://play.golang.org/p/QEyDN9vztr
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()
it is empty method table (as interface{}
has no methods) and reference to Message{}
. Taking reference from it returns the reference to this struct so the unmarhal overwrites it with whatever matches interface{}
.
If the data interface{}
variable holds is a pointer itself, then it is optimized in a way that this pointer is used instead creating interface{}
structure. So getting reference to it gives the reference to original variable.
http://play.golang.org/p/KsIS29rUAX
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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