Example of Abstraction using Interfaces in Golang

package main
 
import "fmt"
 
// Define a new data type "Triangle"
type Triangle struct {
	base, height float32
}
 
// Define a new data type "Square"
type Square struct {
	length float32
}
 
// Define a new data type "Rectangle"
type Rectangle struct {
	length, width float32
}
 
// Define a new data type "Circle"
type Circle struct {
	radius float32
}
 
// A method for type "Triangle"
func (t Triangle) Area() float32 {
	return 0.5 * t.base * t.height
}
 
// A method for type "Square"
func (l Square) Area() float32 {
	return l.length * l.length
}
 
// A method for type "Rectangle"
func (r Rectangle) Area() float32 {
	return r.length * r.width
}
 
// A method for type "Circle"
func (c Circle) Area() float32 {
	return 3.14 * (c.radius * c.radius)
}
 
// Define an interface as achieve abstraction
type Area interface {
	Area() float32
}
 
func main() {
	// Declare and assign values to varaibles
	t := Triangle{base: 15, height: 25}
	s := Square{length: 5}
	r := Rectangle{length: 5, width: 10}
	c := Circle{radius: 5}
 
	// Define a variable of type interface
	var a Area
 
	// Assign to the interface a variable of type "Triangle"
	a = t
	fmt.Println("Area of Triangle", a.Area())
 
	// Assign to the interface a variable of type "Square"
	a = s
	fmt.Println("Area of Square", a.Area())
 
	// Assign to the interface a variable of type "Rectangle"
	a = r
	fmt.Println("Area of Rectangle", a.Area())
 
	// Assign to the interface a variable of type "Circle"
	a = c
	fmt.Println("Area of Circle", a.Area())
}