Class 16: Legacy code
Held:
Preliminaries
Related Pages
Updates
News / Etc.
- I forgot the clickers. Maybe Wednesday.
Upcoming work
- For Wednesday:
- Wikipedia on UML. https://en.wikipedia.org/wiki/Unified_Modeling_Language
- Saasbook: 11.2 (Just Enough UML)
- No additional programming assignments.
Good things to do
- SAAC presentation Tuesday at 11am in JRC 101.
- CS Table, Tuesday at noon: Face recognition
- W. Kamau Bell, Tuesday at 6pm, Harris.
- Prazak Quartet, Tuesday, 28 February 2017, 7:30 p.m., Herrick.
- CS Extras, Thursday at 4:15 pm, Summer Code Camps
Preparatory Activity
On a sheet of paper (supplied), answer the following questions.
- What is one compelling point for your side in the global surveillance “debate”?
- What is “legacy code”? (We see lots of definitions within the chapter.)
- List three “code smells” that you regularly notice.
- What is SOFA?
- List three refactoring techniques that you regularly use.
Global Surveillance
“I would like to discuss the idea of global surveillance and where to draw the line. It’s a grey area for me and I’d like to get more opinions on it.”
- Arguing for as much surveillance as possible: MG, CG, NT, AH, SH, YL, EZ, GN
- Arguing for a moderate position: ST, RW, BR
- Arguing for none whatsoever: Everyone else.
Legacy Code
- What, from your perspective, is “legacy code”? (We see lots of definitions within the chapter.)
- Why do we care about it?
- What kinds of maintainance do we worry about for legacy code?
- How do we do this kind of maintainance?
Code Smells
- What are they?
- Why do we care?
- What are some useful smells to look for?
- SOFA (or the inverse thereof - LMMC)
- What are smells that you look for?
- How do we make things smell better?
Refactoring
- What do you see as the key principles of refactoring?
- What do you see as the key techniques we use to refactor?
- Sam’s perspective: There are a few purposes for the list of
refactoring techniques.
- They serve to remind programmers of the kinds of things they can do to make code better.
- They provide us with a vocabulary to talk about the kinds of changes you might make to a program.
- You should be experienced enough as programmers to have your own list of common “code improvements”. What are some of yours?
An Example
We’ll continue our example from last class. What “smells wrong” in this example?
class TimeSetter def self.convert(d) y = 1980 while (d > 365) do if ((y % 400 == 0) || (y % 4 == 0) && (y % 100 != 0)) if (d > 366) d -= 366 y += 1 end else d -= 365 y += 1 end end return [y,d] end end
Another Example
From Fields et al., _Refactoring: Ruby Edition,, pp. 2-4.
class Movie REGULAR = 0 NEW_RELEASE = 1 CHILDRENS = 2 attr_reader :title attr_accessor :price_code def initialize(title, price_code) @title, @price_code = title, price_code end end class Rental attr_reader :movie, :days_rented def initialize(movie, days_rented) @movie, @days_rented = movie, days_rented end end class Customer attr_reader :name def initialize(name) @name = name @rentals = [] end def add_rental(arg) @rentals << arg end def statement total_amount, frequent_renter_points = 0, 0 result = "Rental Record for #{@name}\n" @rentals.each do |element| this_amount = 0 # determine amounts for each line case element.movie.price_code when Movie::REGULAR this_amount += 2 this_amount += (element.days_rented - 2) * 1.5 if element.days_rented > 2 when Movie::NEW_RELEASE this_amount += element.days_rented * 3 when Movie::CHILDRENS this_amount += 1.5 this_amount += (element.days_rented - 3) * 1.5 if element.days_rented > 3 end # add frequent renter points frequent_renter_points += 1 # add bonus for a two day new release rental if element.movie.price_code == Movie.NEW_RELEASE && element.days_rented > 1 frequent_renter_points += 1 end # show figures for this rental result += "\t" + element.movie.title + "\t" + this_amount.to_s + "\n" total_amount += this_amount end # add footer lines result += "Amount owed is #{total_amount}\n" result += "You earned #{frequent_renter_points} frequent renter points" result end end