Golang动态创建成员Struct

Question

I am fairly new to Golang. I know there is Struct in Golang. But for all I know, you have to define struct

type Circle struct{
    x,y,r float64
}

I am wondering how you can declare a new variable that doesn't exist in the Struct

circle := new(Cirlce)
circle.color = "black"

Thx in advance.

Answer 1

You will need to use a map (of type map[string]interface{}) to work with dynamic JSON. Here is an example of creating a new map:

// Initial declaration
m := map[string]interface{}{
    "key": "value",
}

// Dynamically add a sub-map
m["sub"] = map[string]interface{}{
    "deepKey": "deepValue",
}

Unmarshalling JSON into a map looks like:

var f interface{}
err := json.Unmarshal(b, &f)

The code above would leave you with a map in f, with a structure resembling:

f = map[string]interface{}{
    "Name": "Wednesday",
    "Age":  6,
    "Parents": []interface{}{
        "Gomez",
        "Morticia",
    },
}

You will need to use a type assertion to access it, otherwise Go won't know it's a map:

m := f.(map[string]interface{})

You will also need to use assertions or type switches on each item you pull out of the map. Dealing with unstructured JSON is a hassle.

More information:

• https://blog.golang.org/json-and-go
• https://godoc.org/encoding/json#Unmarshal