Changes for page Code Example: Data Structure Style vs. Object Style

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...	...	@@ -1,32 +1,42 @@
	1	+### Use Cases
	2	+
	3	+This example is intended to demonstrate the extensibility differences between data structures and objects by extending them with
	4	+
	5	+1. an Area() function (extending behavior)
	6	+1. a rectangle type (extending data type)
	7	+
1	1	### Data Structure Style
2	2
3		- type Square struct {
	10	+ interface GeometricObject {}
	11	+
	12	+ class Square implements GeometricObject {
4	4	length float
5	5	}
6	6
7		- type Circle struct {
	16	+ class Circle implements GeometricObject {
8	8	radius float
9	9	}
10	10
11		- func Area(g GeometricObject) float {
	20	+ function Circumference(g GeometricObject) float {
12	12	switch type(g):
13	13	case Square:
14		- return g.length * g.length
15		- case Circle:
16		- return PI * g.radius * g.radius
17		- }
18		-
19		- func Circumference(g GeometricObject) float {
20		- switch type(g):
21		- case Square:
22	22	return 4 * g.length
23	23	case Circle:
24	24	return 2 * PI * g.radius
25	25	}
26	26
	28	+1. Adding an Area() function with a very similar anatomy to Circumference() is easy because it only requires adding new code.
	29	+1. Adding a new datatype, Rectangle, is harder because it requires touching existing code, namely any functions like Circumference() or Area() that need to be enabled handle this datatype.
	30	+
	31	+####
	32	+
27	27	#### Object-Oriented Style
28	28
29		- class Square {
	35	+ interface GeometricObject {
	36	+ Circumference() float
	37	+ }
	38	+
	39	+ class Square implements GeometricObject {
30	30	length float
31	31
32	32	constructor(length float) {
...	...	@@ -33,16 +33,12 @@
33	33	this.length = length
34	34	}
35	35
36		- func Area() float {
37		- return this.length * this.length
38		- }
39		-
40	40	func Circumference() float {
41	41	return 4 * this.length
42	42	}
43	43	}
44	44
45		- class Circle {
	51	+ class Circle implements GeometricObject {
46	46	radius float
47	47
48	48	constructor(radius float) {
...	...	@@ -49,11 +49,15 @@
49	49	this.radius = radius
50	50	}
51	51
52		- func Area() float {
53		- return PI * this.radius * this.radius
54		- }
55		-
56	56	func Circumference() float {
57	57	return 2 * PI * this.radius
58	58	}
59	59	}
	62	+
	63	+1. Adding a function Area() to the GeometricObject interface is hard because it requires touching existing code, namely extending all Square and Circle classes with the new function.
	64	+1. Adding a new datatype, Rectangle, is easy because only new code is added, namely a Rectangle class.
	65	+
	66	+### Conclusion
	67	+
	68	+* The lesson learned here is that data structures are easy to extend with functions, and objects are easy to extend with data types.
	69	+* Although the difference between the two styles may seem insignificant in this simplified example, it has serious implications in complex production codebases with multiple data types and behaviors.