Agile Design

Requirements change and softwares rot.
We can write code more resilient to changes.

Transcript

1. Agile Design
2. Softwares rot • Difficult to change • Fragile • Dependencies • Needless Complexity • Needless Repetition • Difficult to understand
3. The COPY Program
4. Requirements Write a program that copies characters from the keyboard to the printer.
5. The initial design Copy Read Keyboard Write Printer char char
6. Version 1 of Copy program 1 def copy 2 while c = Keyboard.read do 3 Printer.write(c) 4 end 5 end
7. Change requirements The Copy program should also be able to read from paper tape reader.
8. First modification of Copy program 1 pt_flag = false 2 3 def copy 4 while c = (pt_flag ? PaperTape.read : Keyboard.read) do 5 Printer.write(c) 6 end 7 end
9. Give ‘em an inch The customers would sometimes like the Copy program to output to the paper tape punch.
10. Second modification of Copy program 1 pt_flag = false 2 punch_flag = false 3 4 def copy 5 while c = (pt_flag ? PaperTape.read : Keyboard.read) do 6 punch_flag ? Punch.write(c) : Printer.write(c) 7 end 8 end
11. Responding to change 1 class KeyboardReader 2 def read 3 Keyboard.read 4 end 5 end 6 7 8 def copy(reader=DefaultReader) 9 while c = reader.read do 10 Printer.write(c) 11 end 12 end
12. Agile Design A process, not an event Continuous improvement Principles, patterns, practices Keeping the design clean
13. Books • Agile Software Development, Principles, Patterns, and Practices, by Robert C. Martin • Working Effectively with Legacy Code, by Michael Feathers