How to pass a custom comparator to “sort”?

Question

Class A has the following comparator:

class A
  attr_accessor x

  def my_comparator(a)
    x**2 <=> (a.x)**2
  end
end

Answer 1

If you want to reuse these comparators in different places, it would be better to define them as a class, instead of rewriting the same lambda expression every time.

This is based on Java's implementation of Comparable interface:

module Comparator
  def compare(a, b)
    raise NotImplementedError, 'must implement this method'
  end

  def to_proc
    ->(a, b) { compare(a, b) }
  end
end

class LengthComparator
  include Comparator

  def compare(a, b)
    a.length <=> b.length
  end
end

class ReverseLengthComparator < LengthComparator
  def compare(a, b)
    -super
  end
end

You implement your comparison logic in the #compare method. You can then use this class like so: array.sort(&MyCustomComparator.new). It essentially boils down to a lambda expression, but supports more reusability in my opinion.