GIGO: words unreadable aloud

Cheap Ruby memoize using Hash default block

As MenTaLguY mentioned, you can give a block to Hash.new in Ruby. This leads to pretty simple memoization. E.g.,

# Demonstrate a "memoizing" behavior of certain Hash usage
def fib_n ( n )
    if n <= 1
        n
    else
        fib_n( n-1 ) + fib_n( n-2 )
    end
end
$fib_mh = Hash.new do |h,n|
        if n <= 1
            h[n] = n
        else
            h[n] = fib_m( n-1 ) + fib_m( n-2 )
        end
    end
def fib_m ( n )
    $fib_mh[ n ]
end
def compar (lim)
    # puts lim
    strt = Time.now
    puts fib_n(lim)
    mid = Time.now
    puts fib_m(lim)
    last= Time.now
    puts "Lim(#{lim}), no memoing, takes #{mid-strt} seconds."
    puts "Lim(#{lim}), memoing, takes #{last-mid} seconds."
end
compar( ARGV[0].to_i )

Unless you have a lot of time, don't try running this with an argument bigger than the mid-30s.

The RAA has a memoize mixin, but it doesn't use quite the same trick. It's still pretty short, though. The guts:

module Memoize
   MEMOIZE_VERSION = "1.1.0"
   def memoize(name)
      meth = method(name)
      cache = {}
      (class << self; self; end).class_eval do
         define_method(name) do |*args|
            cache.has_key?(args) ? cache[args] : cache[args] ||= meth.call(*args)
         end
      end
      cache
   end
end

11:56:34 PM comment/