Module: Nanoc3::Memoization

Included in:
Compiler, Item, Layout, OutdatednessChecker, RuleMemoryCalculator, RulesCollection
Defined in:
lib/nanoc3/base/memoization.rb

Overview

Adds support for memoizing functions.

Since:

  • 3.2.0

Instance Method Summary collapse

Instance Method Details

#memoize(method_name) ⇒ void

This method returns an undefined value.

Memoizes the method with the given name. The modified method will cache the results of the original method, so that calling a method twice with the same arguments will short-circuit and return the cached results immediately.

Memoization assumes that the current object as well as the function arguments are immutable. Mutating the object or the arguments will not cause memoized methods to recalculate their results. There is no way to un-memoize a result, and calculation results will remain in memory even if they are no longer needed.

Examples:

A fast fib function due to memoization


class FibFast

  extend Nanoc3::Memoization

  def run(n)
    if n == 0
      0
    elsif n == 1
      1
    else
      run(n-1) + run(n-2)
    end
  end
  memoize :run

end

Parameters:

  • method_name (Symbol, String) —

    The name of the method to memoize

Since:

  • 3.2.0



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# File 'lib/nanoc3/base/memoization.rb', line 43

def memoize(method_name)
  # Alias
  original_method_name = '__nonmemoized_' + method_name.to_s
  alias_method original_method_name, method_name

  # Redefine
  define_method(method_name) do |*args|
    # Get cache
    @__memoization_cache ||= {}
    @__memoization_cache[method_name] ||= {}

    # Recalculate if necessary
    if !@__memoization_cache[method_name].has_key?(args)
      result = send(original_method_name, *args)
      @__memoization_cache[method_name][args] = result
    end

    # Done
    @__memoization_cache[method_name][args]
  end
end