Open close principle implemented in golang

main.go

// https://longka.info/blog/2020/08/13/solid-open-close-principle-implemented-in-golang/

package main

import (
        "fmt"
        "math"
       )

type Shape interface {
    GetArea() float64
}

type Square struct {
    Width float64
}

func (s Square) GetArea() float64 {
    return s.Width*s.Width
}

type Circle struct {
    Radius float64
}

func (c Circle) GetArea() float64 {
    return c.Radius * c.Radius * math.Pi
}

type Rectangle struct {
    Length float64
    Width float64
}

func (r Rectangle) GetArea() float64 {
    return r.Width * r.Length
}

type ShapeManager struct {
   shapes    []Shape
}

func (smgr *ShapeManager) AddShape(shape Shape) {
   smgr.shapes = append(smgr.shapes, shape)
}

func (smgr ShapeManager) GetTotalArea() float64 {
    total := 0.0
    for _, shape := range smgr.shapes {
        total += shape.GetArea()
    }
    return total
}

func NewShapeManager() ShapeManager {
    smgr := ShapeManager{}
    smgr.shapes = []Shape{}
    return smgr
}

func main() {
    square := Square{10.0}
    circle := Circle{12.0}

    shapeManager := NewShapeManager()
    shapeManager.AddShape(square)
    shapeManager.AddShape(circle)
    fmt.Printf("shapeManager %+v\n", shapeManager)

    fmt.Println("Square Area ", square.GetArea())
    fmt.Println("Circle Area ", circle.GetArea())
    fmt.Println("Shape Manager Total Area ", shapeManager.GetTotalArea())

    // add rectangle
    rect := Rectangle{5.0, 6.0}
    fmt.Println("Rectangle Area ", rect.GetArea())

    shapeManager.AddShape(rect)
    fmt.Printf("shapeManager %+v\n", shapeManager)

    fmt.Println("Shape Manager Total Area ", shapeManager.GetTotalArea())
}

// https://longka.info/blog/2020/08/13/solid-open-close-principle-implemented-in-golang/