Infinite Cache: Python vs. Ruby

infinite_cache.py

# In Python:
from collections import defaultdict

def infinite_cache():
    cache = lambda: defaultdict(cache)
    return cache()

cache = infinite_cache()

infinite_cache.rb

# In Ruby:
cache = Hash.new do |h,k|
  h[k] = Hash.new(&h.default_proc)
end


# Or, if you want to mimic the Python version:
def infinite_cache
  block = lambda {|h,k| h[k] = Hash.new(&block) }
  Hash.new(&block)
end

cache = infinite_cache


# Mimic it even further, as Ruby's Hash doesn't have quite the same behavior as Python's "defaultdict" wrapper:
class DefaultHash < Hash
  def initialize(value=nil, &block)
    value ||= block

    case value
    when Proc, Method then self.default_proc = proc {|h,k| h[k] = value.call }
    when Class        then self.default_proc = proc {|h,k| h[k] = value.new  }
    else
      self.default = value
    end
  end
end

def infinite_cache
  cache = proc{ DefaultHash.new(cache) }
  cache[]
end

cache = infinite_cache