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Example of Abstraction using Interfaces in Golang

Golang is quite capable of implementing higher level abstractions, but the language designers chose not to implement certain abstractions into the programming language itself. You can use interfaces to create common abstraction that can be used by multiple types. Interfaces define one or more method declarations that must be satisfied to be compatible with the interface.
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())
}