interfaces-typeOf-variable.go

package main

import (
	"fmt"
	"strconv"
)

type Element interface{}
type List []Element

type Person struct {
	name string
	age  int
}

func (p Person) String() string {
	return "(name: " + p.name + " - age: " + strconv.Itoa(p.age) + " years)"
}

func main() {
	list := make(List, 3)
	list[0] = 1       // an int
	list[1] = "Hello" // a string
	list[2] = Person{"Dennis", 70}

	/*
		for index, element := range list {
			if value, ok := element.(int); ok {
				fmt.Printf("list[%d] is an int and its value is %d\n", index, value)
			} else if value, ok := element.(string); ok {
				fmt.Printf("list[%d] is a string and its value os %s\n", index, value)
			} else if value, ok := element.(Person); ok {
				fmt.Printf("list[%d] is a Person and its value is %s\n", index, value)
			} else {
				fmt.Printf("list[%d] is of a deifferent type\n")
			}
		}
	*/

	// We'd better use switch
	for index, element := range list {
		switch value := element.(type) {
		case int:
			fmt.Printf("list[%d] is an int and its value is %d\n", index, value)
		case string:
			fmt.Printf("list[%d] is an int and its value is %s\n", index, value)
		case Person:
			fmt.Printf("list[%d] is an int and its value is %s\n", index, value)
		default:
			fmt.Printf("list[%d] is of a different type\n", index)
		}
	}
}

/*
One thing to remember is that element.(type) cannot be used outside of the switch body,
which means in that case you have to use the comma-ok pattern .
*/