How to f*ck_up_the_refactoring - Andrii Savchenko

How to f*ck up
the refactoring
The ultimate guide
Saturday, April 6, 13

Situation

•2 developers

•2 developers
•2 projects

•2 developers
•2 projects
•Near the same stage

Project1
• Written by novice

Project1
• Full of code duplication

Project1
• Full of code duplication
• Denormalized data structure

Project1
Still maintainable

Project2
• Written by more experienced developer

Project2
• No code duplication

Project2
• No code duplication
• No data duplication

Project2
Maintainable through rewrite

@ptico
}Github
Twitter
LinkedIn
Andrey Savchenko
Aejis

Refactoring
anti-patterns

“IDD”
Intuition Driven Development

lib/extensions.rb________
class Hash
def to_ostruct
# Convert text to ostruct
end
end
module Wicked::Controller::Concerns::RenderRedirect
def process_resource!(resource)
# processing staff
end
end

app/controllers/application_controller.rb
module AjaxActions
def users_list
render :json => @users
end
end

lib/model_helper.rb
module ModelHelpers
def as_json(*)
super(:include => :logs)
end
end

Howtoprevent
• Do not do refactor unless you know
exactly what you do
• Do not assign refactor tasks to the juniors
• Learn design patterns

“DRY Madness”

DRY does not mean “don’t type the
same characters twice”‟David Chelimsky

Bad
%(foo bar baz).each do |name|
define_method(:"set_#{name}") do |val|
val = val.to_s if name == "bar"
name = :"#{name}_name"
self.prev[name] = self.attributes[name]
self.attributes[name] = val
end
end

Good
def set_attribute(name, val)
prev[name] = attributes[name]
attributes[name] = val
end
def set_foo(val)
set_attribute(:foo_name, val)
end
def set_bar(val)
set_attribute(:bar_name, val.to_s)
end
def set_baz(val)
set_attribute(:baz_name, val)
end

tasks.do_the_task(:special, "foo")
tasks.do_the_task(:ordinal, "bar")
def do_the_task(type, val)
if type == :special
val = convert_val_for_special(val)
end
if type == :ordinal && val.is_a?(String)
self.is_string = true
end
self.type = type
self.state = :done
self.val = val
save
end
Bad

Good
def do_special_task(val)
val = convert_val_for_special(val)
persist_task(:special, val)
end
def do_ordinal_task(val)
self.is_string = true if val.is_a?(String)
persist_task(:ordinal, val)
end
def do_another_task
persist_task(:another, val)
end
def persist_task(type, val)
self.type = type
self.state = :done
self.val = val
save
end

Howtoprevent
• Don’t afraid to type twice - afraid to
implement twice
• Avoid metaprogramming
• Avoid metaprogramming

“Frankenstein”

class PigLivery
def filter(blood)
# do important things
end
end
class Pig
def initialize
@livery = PigLivery.new
# ...
end
end

- class PigLivery
+ class PigHumanLivery
class Human
def initialize
@livery = PigHumanLivery.new
# ...
end
end
def initialize
if for_human?
resize_a_bit
end
end

class FrankensteinMonster
def initialize
@livery = PigHumanLivery.new
@eyes = CatDogEyes.new
@jaw = MonkeyJaw.new
# ...
end
end

Howtoprevent
• Use OOP superpower (subclassing instead
conditions, etc.)
• Follow the interface segregation principle

“General content”

class GeneralContent
# Attrs: title, body, coords, tags
end
class Page < GeneralContent
# Uses: title, body, tags
end
class City < GeneralContent
# Uses: title, body, coords
end
class Hotel < GeneralContent
# Uses: title, coords, stars, tags
end

Howtoprevent
• Do not rebuild data structure while
business requirements is not ﬁnalized
• If you consciously do something like this —
try to change your profession

Common tips

Don’trefactor onearly
stages

You have enought time


Learndesign patterns
andprinciples

SOLID
GRASP
YAGNI

Usecommonsense

Questions?
Attributions:
Linecons by Sergey Shmidt
http://www.flickr.com/photos/amyn-design/8548659957/
http://www.flickr.com/photos/greenflames09/100781977/
Andrey Savchenko
Aejis
@ptico

How to f*ck_up_the_refactoring - Andrii Savchenko

How to f*ck_up_the_refactoring - Andrii Savchenko

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