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 here is that data structures are easy to extend with functions and hard to extend with data type, and objects are easy to extend with other objects but hard to extend with functionality.
	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.