Polymorphism in GoLang

// Golang program to illustrate the
// concept of interfaces

package main

import (
    "fmt"
)

// defining an interface
type Figure interface{

    Area() float64
}

// declaring a struct
type Rectangle struct{
    
    // declaring struct variables
    length float64
    width float64
}

// declaring a struct
type Square struct{
    
    // declaring struct variable
    side float64
}

// function to calculate
// area of a rectangle
func (rect Rectangle) Area() float64{

    // Area of rectangle = l * b
    area := rect.length * rect.width
    return area
}

// function to calculate
// area of a square
func (sq Square) Area() float64{
    
    // Area of square = a * a
    area := sq.side * sq.side
    return area
}

// main function
func main() {
    
    // declaring a rectangle instance
    rectangle := Rectangle{
    
        length: 10.5,
        width: 12.25,
    }
    
    // declaring a square instance
    square := Square{
    
        side: 15.0,
    }
    
    // The Figure interface can hold rectangle and square type as they both implements the interface
    var f1 Figure = rectangle
    var f2 Figure = square
      
    // printing the calculated result
    fmt.Printf("Area of rectangle: %.3f unit sq.\n", f1.Area())
    fmt.Printf("Area of square: %.3f unit sq.\n", f2.Area())
}

// Golang program to illustrate the
// concept of polymorphism
package main

import (
    "fmt"
)

// defining an interface
type Reading interface{

    // declaring interface method
    reading_time() int
}

// declaring a struct
type Book struct{
    
    // declaring struct variables
    name string
    page_count int
}

// declaring a struct
type Newspaper struct{

    // declaring struct variables
    name string
    page_count int
}

// declaring a struct
type Magazine struct{

    // declaring struct variables
    name string
    page_count int
}

// function to calculate reading
// time for book 
func (book Book) reading_time() int {
    
    // taking average speed
    // of 10 mins per page
    read_time := 10 * book.page_count
    return read_time
}

// function to calculate reading
// time for newspaper
func (newspaper Newspaper) reading_time() int {

    // taking average speed
    // of 30 mins per page
    read_time := 30 * newspaper.page_count
    return read_time
}

// function to calculate reading
// time for magazine
func (magazine Magazine) reading_time() int {
    
    // taking average speed
    // of 5 mins per page
    read_time := 5 * magazine.page_count
    return read_time
}

// function to calculate reading time
func calcReadingTime(ReadingTime []Reading) int {

        totalTime := 0
    
    // looping through elements
    // of the Reading array    
        for _, t := range ReadingTime {
        
        // run time polymorphism, call to 
        // method depends on object being
        // referred at run time
            totalTime += t.reading_time() 
        }
    
        return totalTime
}

// main function
func main() {
    
    // declaring a book instance
    book1 := Book{
        name: "Goosebumps", 
        page_count: 150,
    }
    
    // declaring a newspaper instance
    newspaper1 := Newspaper{
        name: "TOI",
        page_count: 12,
    }
    
    // declaring a magazine instance
    magazine1 := Magazine{
        name: "Forbes",
        page_count: 40,
    }
    
    // array of type Reading interface
    ReadingTime := []Reading{book1, newspaper1, magazine1}
    
    // total reading time calculated
        totalTime := calcReadingTime(ReadingTime)
    
    // Printing total time for reading
        fmt.Printf("Total Time is %d minutes.\n", totalTime)
}