Ruby Extended Array class that supports full method chain

Question

Short:

Is there a way to create extended Array class named A, that supports full method chain with map, sort, sort_by and new method word and does not harm Array class?

Example:

 [
    A.new(a).word,
    A.new(a).sort.word,
    A.new(a).sort_by(&:-@).word,
    A.new(a).map(&:chr).sort.map(&:ord).word
  ]

Long story:

I solved this kata and created code that extends Array class with new word method:

class Array
  def word
    [*self[0..1],*self[-2..-1]].map(&:chr).join
  end
end
def sort_transform(a)
  [
    a.word,
    a.sort.word,
    a.sort_by(&:-@).word,
    a.map(&:chr).sort.map(&:ord).word
  ].join ?-
end

Then I thought this is not a good idea to add method for such kind of base classes. And I tried to implement new class that inherited all behavior from an Array.

class A < Array
  def word
    [*self[0..1],*self[-2..-1]].map(&:chr).join
  end
end

This addition breaks my code, because map, sort, sort_by returns an Array instance: A.new([1,2,3]).sort.class # Array. And Array does not understand a word method. And instead of A.new(a).sort.word I have to encapsulate part of chain into a A.new constructor: A.new(a.sort).word. That's definitely breaks pure method chain.

Is it possible to extend Array such way to reach pure method chains like this; A.new(a).sort.word?

When I tried to write line this: class A < Array

def word
    [*self[0..1],*self[-2..-1]].map(&:chr).join
  end
  def sort
    A.new(self.sort)
  end
end

This brings me main.rb:8:in 'sort': stack level too deep (SystemStackError) Finally already writing this lines I found a way to avoid deep stack: converting self to Array and then again convert it to A.

class A < Array
  def word
    [*self[0..1],*self[-2..-1]].map(&:chr).join
  end
  def sort
    A.new(self.to_a.sort)
  end
end

So is It an only way to implement such extension?

The article was given to me words.steveklabnik.com/beware-subclassing-ruby-core-classes And developer who gave me this article told that instances cast back to Array in method chain in Ruby because of C code. It implements for speed. — Dmitry Dmitriev
– Dmitry Dmitriev, Commented Jul 4, 2019 at 6:06
I'd use a refinement on Array instead. Why does no-one use refinements? — Amadan
– Amadan, Commented Jul 4, 2019 at 6:18
@Amadan this why I wrote this question :) To get information you gave. — Dmitry Dmitriev
– Dmitry Dmitriev, Commented Jul 4, 2019 at 6:25
Why would you add an instance method to Array, subclass Array or refine Array. Why not just define a method word with one argument for the given array? — Cary Swoveland
– Cary Swoveland, Commented Jul 4, 2019 at 21:19
@CarySwoveland: Why would you not refine? That's why they're for. Why refine over a function? Because it chains better, and chaining reads more naturally since it linearly represents causality. f.each_line.map(&:length).max has flow. find_max(get_lines(f).map(&:length)) goes back and forth and incurs a higher mental load. The non-parallelism between syntax and execution order is one of the reasons why I dislike Python: why is len a function but lower a method but map a function but join a method on string but sorted a function but sort a method... And comprehensions... >.< — Amadan
– Amadan, Commented Jul 10, 2019 at 10:27

Amadan · Accepted Answer · 2019-07-04 06:31:41Z

4

If you ever want to monkey-patch a core class but you think it's icky, you should remember that refinements are made just for this scenario.

module ArrayWithWord
  refine Array do
    def word
      [*self[0..1],*self[-2..-1]].map(&:chr).join
    end
  end
end

class WordTest
  using ArrayWithWord

  # [].word works here
  def self.sort_transform(a)
    [
      a.word,
      a.sort.word,
      a.sort_by(&:-@).word,
      a.map(&:chr).sort.map(&:ord).word
    ].join ?-
  end
end

WordTest.sort_transform(%w(foo bar baz quux))
# => "fbbq-bbfq-bbfq-bbfq"

# [].word doesn't work here
[].word
# => NoMethodError (undefined method `word' for []:Array)

answered Jul 4, 2019 at 6:31

Amadan

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