c3.go

package main

import "fmt"

// Shape is the interface that all shapes must implement
type Shape interface {
	Area() float64
}

// Rectangle represents a rectangle shape
type Rectangle struct {
	Width  float64
	Height float64
}

// Area calculates the area of a rectangle
func (r *Rectangle) Area() float64 {
	return r.Width * r.Height
}

// Circle represents a circle shape
type Circle struct {
	Radius float64
}

// Area calculates the area of a circle
func (c *Circle) Area() float64 {
	return 3.14159 * c.Radius * c.Radius
}

// CompositeShape represents a composite shape that can contain other shapes
type CompositeShape struct {
	Shapes []Shape
}

// Area calculates the area of a composite shape by summing the areas of its child shapes
func (c *CompositeShape) Area() float64 {
	var area float64
	for _, shape := range c.Shapes {
		area += shape.Area()
	}
	return area
}

func main() {
	rect := &Rectangle{Width: 10, Height: 5}
	circle := &Circle{Radius: 3}
	composite := &CompositeShape{Shapes: []Shape{rect, circle}}
	fmt.Println("Area of composite shape:", composite.Area()) // prints "Area of composite shape: 34.9159"
}