嵌入式结构的多态JSON解组 [英] Polymorphic JSON unmarshalling of embedded structs

问题描述

这里是一个示例(另请参见 https://play.golang.org/p/or7z4Xc8tN ):

Here is an example (see also https://play.golang.org/p/or7z4Xc8tN):

package main

import (
    "encoding/json"
    "fmt"
)

type A struct {
    X string
    Y int
}

type B struct {
    A
    Y string 
}

func main() {
    data := []byte(`{"X": "me", "Y": "hi"}`)
    b := &B{}
    json.Unmarshal(data, b)
    fmt.Println(b)
    fmt.Println(b.A)

    b = &B{}
    data = []byte(`{"X": "me", "Y": 123}`)
    json.Unmarshal(data, b)
    fmt.Println(b)
    fmt.Println(b.A)
}

哪个输出:

&{{me 0} hi}
{me 0}
&{{me 0} }
{me 0}

是否有一种方法可以将字段Y多态解组为int或字符串?甚至因为定义了B.Y就完全取消了对A.Y的编组?

Is there a way to polymorphically unmarshal the field Y to either an int or a string? Or even unmarshal into A.Y at all since B.Y is defined?

我知道有些人可能建议使用诸如json.Unmarshall(data, &b.A)之类的工具进行编组，但是我不知道我是否可以将其适合我的当前设计.

I know some might suggest unmarshalling with something like json.Unmarshall(data, &b.A), but I don't know if I can fit that into my current design.

推荐答案

Go唯一的多态性是接口.嵌入不提供多态性.

Go's only polymorphism is interfaces. Embedding does not offer polymorphism.

如果您试图在无法假设某个字段将是哪种类型的情况下解组JSON，则可以将interface{}类型的字段与类型断言，fmt.Sprint或反射类型一起使用.您应该使用哪个取决于特定的用例-一旦获得了价值，您将如何处理它?在某些时候，您必须注意它是int还是string，这将决定如何处理该值.

If you're trying to unmarshal JSON where you can't assume what type one of the fields is going to be, you can use a field of type interface{} along with type assertions, fmt.Sprint, or reflection. Which you should use depends on the particular use case - once you've got the value, what are you going to do with it? At some point you have to care if it's an int or a string, which will determine how you handle the value.

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