Go的。（type）取消编组JSON时发生意外

Question

I'm RTFMing, specifically the section on Decoding Arbitrary Go Data. Based on that section, I've written the following test program

var f interface{}

json.Unmarshal(
  []byte(`{"Name":"Wednesday","Age":6,"Parents":["Gomez","Morticia"]}`), &f)  

m := f.(map[string]interface{}) 
for k, v := range m {
    switch vv := v.(type) {
    case string:
        fmt.Println(k, "is string", vv)
    case int:
        fmt.Println(k, "is int", vv)
    case []interface{}:
        fmt.Println(k, "is an array:")
        for i, u := range vv {
            fmt.Println(i, u)
        }
    default:
        fmt.Println(k, "is of a type I don't know how to handle")
        fmt.Println("    Type Is:", vv)
    }
}

That is, I declare a variable with an empty interface type. Per the docs, I

use a type assertion to access f's underlying map[string]interface{}:

Then, I use range to do a for loop over the map's key/value pairs. If the value is a string, int, or []interface, the program says so. If that value is another type, (the default case), the program says I don't know how to handle it. This is almost verbatim code from the manual.

The program produces the following output.

Name is string Wednesday
Age is of a type I don't know how to handle
    Type Is: 6
Parents is an array:
0 Gomez
1 Morticia

That is -- it correctly identifies the types of strings and arrays -- for for some reason it seems like the type of the parsed 6 isn't and int -- it's 6.

So -- I guess my question is either *why does v.(type) return the actual number oinstead of int here or my question is why is that the wrong question?

Answer 1

JSON numbers are double precision floats, so the default type go uses is float64. You can see the defaults listed in the json.Unmarshal documentation.