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

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...	...	@@ -1,28 +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 {
8		- length float
	16	+ class Circle implements GeometricObject {
	17	+ radius float
9	9	}
10	10
11		- func Area(g GeometricObject) float {
12		- switch (g.type()):
13		- case Circle:
14		- return
	20	+ function Circumference(g GeometricObject) float {
	21	+ switch type(g):
15	15	case Square:
16		- return ...
	23	+ return 4 * g.length
	24	+ case Circle:
	25	+ return 2 * PI * g.radius
17	17	}
18		-
19		- func Circumference(g GeometricObject) float {
20		- ...
21		- }
22	22
	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	+
23	23	#### Object-Oriented Style
24	24
25		- class Square {
	35	+ interface GeometricObject {
	36	+ Circumference() float
	37	+ }
	38	+
	39	+ class Square implements GeometricObject {
26	26	length float
27	27
28	28	constructor(length float) {
...	...	@@ -29,16 +29,12 @@
29	29	this.length = length
30	30	}
31	31
32		- func Area() float {
33		- return this.length * this.length
34		- }
35		-
36	36	func Circumference() float {
37	37	return 4 * this.length
38	38	}
39	39	}
40	40
41		- class Circle {
	51	+ class Circle implements GeometricObject {
42	42	radius float
43	43
44	44	constructor(radius float) {
...	...	@@ -45,11 +45,15 @@
45	45	this.radius = radius
46	46	}
47	47
48		- func Area() float {
49		- return PI * this.radius * this.radius
50		- }
51		-
52	52	func Circumference() float {
53	53	return 2 * PI * this.radius
54	54	}
55	55	}
	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.