Interfaces

This Go program demonstrates the use of interfaces and polymorphism. It defines an interface named geometry with methods area and perim. Two struct types, rect and circle, implement this interface by providing their own versions of the area and perim methods. The measure function takes a geometry interface as a parameter and calls its methods. Finally, in the main function, instances of rect and circle are created, and the measure function is called on each of them.

Let's go through each part of the code with inline comments and additional explanations:

package main

import (
    "fmt"
    "math"
)

// Define an interface named 'geometry' with methods 'area' and 'perim'
type geometry interface {
    area() float64
    perim() float64
}

// Define a struct named 'rect' with two fields: 'width' and 'height'
type rect struct {
    width, height float64
}

// Define a struct named 'circle' with a field 'radius'
type circle struct {
    radius float64
}

// Implement the 'area' method for the 'rect' struct
func (r rect) area() float64 {
    return r.width * r.height
}

// Implement the 'perim' method for the 'rect' struct
func (r rect) perim() float64 {
    return 2*r.width + 2*r.height
}

// Implement the 'area' method for the 'circle' struct
func (c circle) area() float64 {
    return math.Pi * c.radius * c.radius
}

// Implement the 'perim' method for the 'circle' struct
func (c circle) perim() float64 {
    return 2 * math.Pi * c.radius
}

// Function 'measure' takes a 'geometry' interface and prints information about it
func measure(g geometry) {
    fmt.Println(g)
    fmt.Println("Area:", g.area())
    fmt.Println("Perimeter:", g.perim())
}

func main() {
    // Create an instance of the 'rect' struct
    r := rect{width: 3, height: 4}

    // Create an instance of the 'circle' struct
    c := circle{radius: 5}

    // Call 'measure' function for the 'rect' instance
    measure(r)

    // Call 'measure' function for the 'circle' instance
    measure(c)
}

Output

{3 4}
12
14
{5}
78.53981633974483
31.41592653589793

Explanation:

1. The geometry interface is defined with two methods, area and perim.

2. Two struct types, rect and circle, implement the geometry interface by providing their own versions of the area and perim methods.

3. The measure function takes a parameter of type geometry and prints information about it, including calling the area and perim methods.

4. In the main function:

   • An instance of the rect struct (r) and an instance of the circle struct (c) are created.

   • The measure function is called for both the rect and circle instances, demonstrating polymorphism. The function can work with any type that implements the geometry interface, allowing for flexibility and code reusability.