Subclassed-From-Core-Class.md

Subclassed From Core Class

Introduction

Candidate classes for the Subclassed From Core Class smell are classes which inherit from Core Classes like Hash, String and Array.

Inheriting from Core Classes means that you are going to have a bad time debugging (the explanation below is taken from here):

What do you think this code should do?

List = Class.new(Array)

l = List.new
l << 1
l << 2
puts l.reverse.class # => Array

If you said “it prints Array” you’d be right. Let’s talk about a more pernicious issue: Strings.

class MyString < String
  def to_s
    "lol"
  end
end

s = MyString.new
s.concat "Hey"

puts s      # => Hey
puts s.to_s # => lol
puts "#{s}" # => Hey

That’s right! With Strings, Ruby doesn’t call #to_s: it puts the value in directly. Generally speaking, subclassing isn’t the right idea here.

Example

Given

class Ary < Array
end

class Str < String
end

Reek would report the Subclassed From Core Class smell for both classes. Instead of subclassing them you want a data structure that uses one of these core classes internally, but isn’t exactly like one. For instance:

require 'forwardable'

class List
  extend Forwardable
  def_delegators :@list, :<<, :length # and anything else

  def initialize(list = [])
    @list = list
  end

  def reverse
    List.new(@list.reverse)
  end
end

l = List.new
l << 1
l << 2
puts l.reverse.class  # => List

Configuration

Subclassed From Core Class offers the Basic Smell Options.