You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: interfaces_poly.go
    path of file: ./repos/the-way-to-go_ZH_CN/eBook/examples/chapter_11
    
    the code of the file until where you have to start completion: // interfaces_
    
func main() {
	r := Rectangle{5, 3} // Area() of Rectangle needs a value
	q := &Square{5}      // Area() of Square needs a pointer
	shapes := []Shaper{r, q}
	fmt.Println("Looping through shapes for area ...")
	for n := range shapes {
		fmt.Println("Shape details: ", shapes[n])
		fmt.Println("Area of this shape is: ", shapes[n].Area())
	}
}