golang 动态 实例化 结构体

scut1135 · · 7597 次点击 · · 开始浏览    
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真理 http://stackoverflow.com/questions/10210188/instance-new-type-golang

So, if I understand your question correctly, you are asking about how you can create an object when you just have the name of the type as string. So, for example, you might have a string "MyStruct" and you want to create an object of this type.

Unfortunately, that's not easily possible because Go is a statically typed language and the linker will eliminate dead code (or inline parts of it). So, there is no guarantee, that your final executable will even contain the code of "MyStruct".

You can however, maintain a global map[string]reflect.Type manually. For example by initializing this map in the init() function of your packages which defines such discover-able types. This will also tell the compiler that you are using the types. Afterwards, you can use this map to look up the reflect.Type of the type you want to create and use reflect.New to get a pointer to a new object of that type (stored as a reflect.Value). You can extract the object into an interface with something like this:

reflect.New(yourtype).Elem().Interface()

Elem() will de-reference the pointer and Interface() will return the reflected value as an interface{}. See The Laws of Reflection for further details.

PS: There might be a better way to structure your program which doesn't even require reflection and which let the compiler catch more errors. Have you considered using a factory method for example? An other easy solution might be to maintain a map[string]func() interface{} of functions which can be invoked to create a new object with that name.




http://mikespook.com/2012/07/%E5%9C%A8-golang-%E4%B8%AD%E7%94%A8%E5%90%8D%E5%AD%97%E8%B0%83%E7%94%A8%E5%87%BD%E6%95%B0/

但这里有一个限制:这个 map 仅仅可以用原型是“func()”的没有输入参数或返回值的函数。
如果想要用这个方法实现调用不同函数原型的函数,需要用到 interface{}。


***********参考*****************


1.  https://www.socketloop.com/tutorials/golang-fix-type-interface-has-no-field-or-no-methods-and-type-assertions-example

Golang : Fix type interface{} has no field or no methods and type assertions example



2. golang用字符串反射实例化结构体

package main
 
import (
 "fmt"
 "reflect"
)
 
type Foo struct {
}
type Bar struct {
}
 
//用于保存实例化的结构体对象
var regStruct map[string]interface{}
 
func main() {
 str := "Bar"
 if regStruct[str] != nil {
  t := reflect.ValueOf(regStruct[str]).Type()
  v := reflect.New(t).Elem()
  fmt.Println(v)
 }
 
}
 
func init() {
 regStruct = make(map[string]interface{})
 regStruct["Foo"] = Foo{}
 regStruct["Bar"] = Bar{}
}



3. http://stackoverflow.com/questions/17507697/dry-out-my-go-function-with-interfaces


kinds := map[string]func() Entity {
    "user": func() Entity { return &User{} },
    "space": func() Entity { return &Space{} },
    "room": func() Entity { return &Room{} },
}
	
func Create(kind string) {
    instance := kinds[kind]()

    decoder.Decode(instance)

    saveEntity(instance)
}

4.  新手求解 golang 动态new struct 

http://www.oschina.net/question/1388294_141504?sort=default&p=2#answers

<span style="font-size:14px;">我现在是这样做的

var ModelObj map[string]interface{} = map[string]interface{}{

"Member": new(Member), 
} 


func GetModObj(mod string) interface{} { 
if ModelObj[mod] != nil { 
return ModelObj[mod] 
} else { 
return nil 
} 
} </span>


5. http://stackoverflow.com/questions/13856539/how-do-you-get-struct-value-on-unknown-interface




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感谢作者:scut1135

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