How to handle dynamic interface types in Golang?

Question

I am trying to handle dynamic interface type where I don't know whether interface is of type float64 or int64. I am using an API and Decode the response on a map where price is sometimes integer and sometimes float. eg JSON response is sometimes {price: 35} and sometimes {price: 35}

I have created an example code here

package main
import "fmt"

func main() {

    response := make(map[string]interface{})
    response["price"] = 2.1

    response1 := make(map[string]interface{})
    response1["price"] = 2

    price_response, _ := response["price"].(float64)
    price_response1, _ := response1["price"].(float64)

    fmt.Println(price_response, "==> price_response") //output = 2.1
    fmt.Println(price_response1,"==> price_response1") // //output = 0
}

The Output is get is

2.1 price_response
0 price_response1

Now here, I have to define type statically while doing type assertions on interface types. How am I supposed to handle this type issue to avoid getting 0 and instead getting the actual value converted into float64?

Answer 1

How am I supposed to handle this type issue to avoid getting 0 and instead getting the actual value converted into float64?

t, ok := i.(T)

This line of code checks whether the interface value i holds the concrete type T. If not, ok will be false and t will be the zero value of type T

price_response1, _ := response1["price"].(float64)

Here response1["price"] doesn't hold a type float64. Hence price_response1 has zero value of type float64, which is 0.

To print the underlying type of interface{} as a string you can use:

getType := fmt.Sprintf("%T", response1["price"])
fmt.Println(getType) 

See the below code to get the actual value converted into float64, if the underlying type is int:

package main

import "fmt"

func convertToFloat64(resp interface{}) {
    switch v := resp.(type) {
    case int:
        fmt.Println(float64(v), "==> price_response1")

    case float64:
        fmt.Println(v, "==> price_response")
    default:
        fmt.Println("unknown")
    }
}

func main() {
    response := make(map[string]interface{})
    response["price"] = 2.1
    convertToFloat64(response["price"])
    response1 := make(map[string]interface{})
    response1["price"] = 2
    convertToFloat64(response1["price"])

}

Output:

2.1 ==> price_response
2 ==> price_response1