rectangles: Add associated function

rectangles/src/main.rs

@@ -5,6 +5,14 @@ struct Rectangle {
 }
 
 impl Rectangle {
+    fn build_rectangle(width: u32, height: u32) -> Rectangle {
+        Rectangle { width, height }
+    }
+
+    fn square(size: u32) -> Rectangle {
+        Rectangle::build_rectangle(size, size)
+    }
+
     fn area(&self) -> u32 {
         self.width * self.height
     }
@@ -50,6 +58,14 @@ fn main() {
         rect,
         rect.can_hold(&rect),
     );
+
+    let square = Rectangle::square(3);
+
+    println!(
+        "The area of the square rectangle {:#?} is {} square pixels.",
+        square,
+        square.area()
+    );
 }
 
 fn area(width: u32, height: u32) -> u32 {