Polymorphism with Julia using functions, example using type Shape

Program: 

abstract type Shape end

# poymorhpic function computation

function area(shape::Shape)

    throw(MethodError("area() is not implemented for abstract type Shape"))

end

struct Circle <: Shape

    radius::Real

end

function area(c::Circle)

    return 3 * c.radius ^ 2

end

struct Rectangle <: Shape

    width::Real

    height::Real

end

function area(r::Rectangle)

    return r.width * r.height

end

struct Square <: Shape

    width::Real

end

function area(s::Square)

    return s.width * s.width

end

function main()

    shapes = Shape[Circle(1), Square(2), Rectangle(3, 4)]

   

    println("Area Circle(1) = ", area(shapes[1]))

    println("Area Square(2) = ", area(shapes[2]))

    println("Area Rectangle(3, 4) = ", area(shapes[3]))

end

main()

Output:

Area Circle(1) = 3

Area Square(2) = 4   

Area Rectangle(3, 4) = 12