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

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Parent

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1		-Main.WebHome
	1	+Software Engineering.Clean Code.Objects and Data Structures.WebHome

Content

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	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 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.