type_interfaces.go

package main

import (
	"fmt"
	"math"
)

type Square struct {
	side float32
}

type Circle struct {
	radius float32
}

type Shaper interface {
	Area() float32
}

func main() {
	var areaIntf Shaper
	sq1 := new(Square)
	sq1.side = 5

	areaIntf = sq1
	// Is Square the type of areaIntf ?
	if t, ok := areaIntf.(*Square); ok {
		fmt.Printf("The type of areaIntf is: %T\n", t)
	}
	if u, ok := areaIntf.(*Circle); ok {
		fmt.Printf("The type of areaIntf is: %T\n", u)
	} else {
		fmt.Println("areaIntf does not contain a variable of type Circle")
	}
	// testing with switch:
	switch t := areaIntf.(type) {
		case *Square:
			fmt.Printf("Type Square %T with value %v\n", t, t)
		case *Circle:
			fmt.Printf("Type Circle %T with value %v\n", t, t)
		/* 
		case bool:
   			fmt.Printf("Type boolean %t\n", t)
		case int:
   			fmt.Printf("Type int %d\n", t)
		case *bool:
   			fmt.Printf("Type pointer to boolean %t\n", *t)
		case *int:
   			fmt.Printf("Type pointer to int %d\n", *t)
		*/
		default:
   			fmt.Printf("Unexpected type %T", t)
	}
}

func (sq *Square) Area() float32 {
	return sq.side * sq.side
}

func (ci *Circle) Area() float32 {
	return ci.radius * ci.radius * math.Pi
}