gogo-server

Golang dynamically creating member of struct

I know there is struct in Go, 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(Circle)
circle.color = "black"
Solution

  • 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: