Unmarshaling JSON text with a long integer number to Struct with field of type interface{}

json-unmarshal-test.go

package main

import (
	"encoding/json"
	"fmt"
)

type container struct {
	Name  string
	Value interface{}
}

type person struct {
	Name   string
	Number uint64
}

func main() {
	// Raw data
	data := "{\"Name\":\"Container\",\"Value\":{\"Name\":\"Joe\",\"Number\":123456789}}"

	c := &container{}

	// After unmarshaling "Number" will be 1.23456789e+08 instead of 123456789
	// As the default Unmarshaling logic is to use float64
	json.Unmarshal([]byte(data), c)
	fmt.Printf("%v\n", c)

	// At this point Value was marshaled into a generic map map[string]interface{}.
	// Therefore, we cannot cast c.Value into a struct of type person.
	// To do that we can Marshal c.Value and unmarshal it into a person struct,
	// however, this will cause an error because the value of "Number" is float
	// and not an integer
	marshaledValue, _ := json.Marshal(c.Value)
	p := &person{}
	if err := json.Unmarshal(marshaledValue, p); err != nil {
		fmt.Printf("%v\n", err)
		return
	}
}