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Contents
# 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](http://words.steveklabnik.com/beware-subclassing-ruby-core-classes)):
> What do you think this code should do?
```Ruby
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.
```Ruby
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
```Ruby
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:
```Ruby
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](Basic-Smell-Options.md).
Version data entries
49 entries across 47 versions & 2 rubygems