Possible help in code refactoring - ruby

Question

Sandi Metz says in SOLID OOPS concepts from GORUCO that presence of if..else blocks in Ruby can be considered to be a deviation from Open-Close Principle. What all methods can be used to avoid not-urgent if..else conditions? I tried the following code:
class Fun
def park(s=String.new)
puts s
end
def park(i=Fixnum.new)
i=i+2
end
end
and found out that function overloading does not work in Ruby. What are other methods through which the code can be made to obey OCP?
I could have simply gone for:
class Fun
def park(i)
i=i+2 if i.class==1.class
puts i if i.class=="asd".class
end
end
but this is in violation to OCP.

Answer 1

With your current example, and wanting to avoid type detection, I would use Ruby's capability to re-open classes to add functionality you need to Integer and String:
class Integer
def park
puts self + 2
end
end
class String
def park
puts self
end
end
This would work more cleanly when altering your own classes. But maybe it doesn't fit your conceptual model (it depends what Fun represents, and why it can take those two different classes in a single method).
An equivalent but keeping your Fun class might be:
class Fun
def park_fixnum i
puts i + 2
end
def park_string s
puts s
end
def park param
send("park_#{param.class.to_s.downcase}", param)
end
end
As an opinion, I am not sure you will gain much writing Ruby in this way. The principles you are learning may be good ones (I don't know), but applying them forcefully "against the grain" of the language may create less readable code, regardless of whether it meets a well-intentioned design.
So what I would probably do in practice is this:
class Fun
def park param
case param
when Integer
puts param + 2
when String
puts param
end
end
end
This does not meet your principles, but is idiomatic Ruby and slightly easier to read and maintain than an if block (where the conditions could be far more complex so take longer for a human to parse).

Answer 2

You could just create handled classes for Fun like so
class Fun
def park(obj)
#parker ||= Object.const_get("#{obj.class}Park").new(obj)
#parker.park
rescue NameError => e
raise ArgumentError, "expected String or Fixnum but recieved #{obj.class.name}"
end
end
class Park
def initialize(p)
#park = p
end
def park
#park
end
end
class FixnumPark < Park
def park
#park += 2
end
end
class StringPark < Park
end
Then things like this will work
f = Fun.new
f.park("string")
#=> "string"
f.instance_variable_get("#parker")
#=> #<StringPark:0x1e04b48 #park="string">
f = Fun.new
f.park(2)
#=> 4
f.instance_variable_get("#parker")
#=> #<FixnumPark:0x1e04b48 #park=4>
f.park(22)
#=> 6 because the instance is already loaded and 4 + 2 = 6
Fun.new.park(12.3)
#=> ArgumentError: expected String or Fixnum but received Float

Answer 3

You could do something like this:
class Parent
attr_reader :s
def initialize(s='')
#s = s
end
def park
puts s
end
end
class Child1 < Parent
attr_reader :x
def initialize(s, x)
super(s)
#x = x
end
def park
puts x
end
end
class Child2 < Parent
attr_reader :y
def initialize(s, y)
super(s)
#y = y
end
def park
puts y
end
end
objects = [
Parent.new('hello'),
Child1.new('goodbye', 1),
Child2.new('adios', 2),
]
objects.each do |obj|
obj.park
end
--output:--
hello
1
2
Or, maybe I overlooked one of your twists:
class Parent
attr_reader :x
def initialize(s='')
#x = s
end
def park
puts x
end
end
class Child1 < Parent
def initialize(x)
super
end
def park
x + 2
end
end
class Child2 < Parent
def initialize(x)
super
end
def park
x * 2
end
end
objects = [
Parent.new('hello'),
Child1.new(2),
Child2.new(100),
]
results = objects.map do |obj|
obj.park
end
p results
--output:--
hello
[nil, 4, 200]
And another example using blocks, which are like anonymous functions. You can pass in the desired behavior to park() as a function:
class Function
attr_reader :block
def initialize(&park)
#block = park
end
def park
raise "Not implemented"
end
end
class StringFunction < Function
def initialize(&park)
super
end
def park
block.call
end
end
class AdditionFunction < Function
def initialize(&park)
super
end
def park
block.call 1
end
end
class DogFunction < Function
class Dog
def bark
puts 'woof, woof'
end
end
def initialize(&park)
super
end
def park
block.call Dog.new
end
end
objects = [
StringFunction.new {puts 'hello'},
AdditionFunction.new {|i| i+2},
DogFunction.new {|dog| dog.bark},
]
results = objects.map do |obj|
obj.park
end
p results
--output:--
hello
woof, woof
[nil, 3, nil]

Answer 4

Look at the is_a? method
def park(i)
i.is_a?(Fixnum) ? (i + 2) : i
end
But even better not to check a type, but use duck typing:
def park(i)
i.respond_to?(:+) ? (i + 2) : i
end
UPD: After reading comments. Yes, both examples above don't solve the OCP problem. That is how I would do it:
class Fun
# The method doesn't know how to pluck data. But it knows a guy
# who knows the trick
def pluck(i)
return __pluck_string__(i) if i.is_a? String
__pluck_fixnum__(i) if i.is_a? Fixnum
end
private
# Every method is responsible for plucking data in some special way
# Only one cause of possible changes for each of them
def __pluck_string__(i)
puts i
end
def __pluck_fixnum__(i)
i + 2
end
end

Answer 5

I understand or equal to operation in ruby but can you explain what
you have done with:
Object.const_get("#{obj.class}Park").new(obj)
In ruby, something that starts with a capital letter is a constant. Here is a simpler example of how const_get() works:
class Dog
def bark
puts 'woof'
end
end
dog_class = Object.const_get("Dog")
dog_class.new.bark
--output:--
woof
Of course, you can also pass arguments to dog_class.new:
class Dog
attr_reader :name
def initialize(name)
#name = name
end
def bark
puts "#{name} says woof!"
end
end
dog_class = Object.const_get("Dog")
dog_class.new('Ralph').bark
--output:--
Ralph says woof!
And the following line is just a variation of the above:
Object.const_get("#{obj.class}Park").new(obj)
If obj = 'hello', the first portion:
Object.const_get("#{obj.class}Park")
is equivalent to:
Object.const_get("#{String}Park")
And when the String class object is interpolated into a string, it is simply converted to the string "String", giving you:
Object.const_get("StringPark")
And that line retrieves the StringPark class, giving you:
Object.const_get("StringPark")
|
V
StringPark
Then, adding the second portion of the original line gives you:
StringPark.new(obj)
And because obj = 'hello', that is equivalent to:
StringPark.new('hello')
Capice?