/ Ruby on Rails
/
method

memoize

memoize(*symbols)
public

No documentation available.

# File activesupport/lib/active_support/memoizable.rb, line 56
    def memoize(*symbols)
      symbols.each do |symbol|
        original_method = "_unmemoized_#{symbol}""_unmemoized_#{symbol}"
        memoized_ivar = ActiveSupport::Memoizable.memoized_ivar_for(symbol)

        class_eval "include InstanceMethods                                                  # include InstanceMethods\n#\nif method_defined?(:\#{original_method})                                  # if method_defined?(:_unmemoized_mime_type)\nraise \"Already memoized \#{symbol}\"                                     #   raise \"Already memoized mime_type\"\nend                                                                      # end\nalias \#{original_method} \#{symbol}                                       # alias _unmemoized_mime_type mime_type\n#\nif instance_method(:\#{symbol}).arity == 0                                # if instance_method(:mime_type).arity == 0\ndef \#{symbol}(reload = false)                                          #   def mime_type(reload = false)\nif reload || !defined?(\#{memoized_ivar}) || \#{memoized_ivar}.empty?  #     if reload || !defined?(@_memoized_mime_type) || @_memoized_mime_type.empty?\n\#{memoized_ivar} = [\#{original_method}.freeze]                     #       @_memoized_mime_type = [_unmemoized_mime_type.freeze]\nend                                                                  #     end\n\#{memoized_ivar}[0]                                                  #     @_memoized_mime_type[0]\nend                                                                    #   end\nelse                                                                     # else\ndef \#{symbol}(*args)                                                   #   def mime_type(*args)\n\#{memoized_ivar} ||= {} unless frozen?                               #     @_memoized_mime_type ||= {} unless frozen?\nreload = args.pop if args.last == true || args.last == :reload       #     reload = args.pop if args.last == true || args.last == :reload\n#\nif defined?(\#{memoized_ivar}) && \#{memoized_ivar}                    #     if defined?(@_memoized_mime_type) && @_memoized_mime_type\nif !reload && \#{memoized_ivar}.has_key?(args)                      #       if !reload && @_memoized_mime_type.has_key?(args)\n\#{memoized_ivar}[args]                                           #         @_memoized_mime_type[args]\nelsif \#{memoized_ivar}                                             #       elsif @_memoized_mime_type\n\#{memoized_ivar}[args] = \#{original_method}(*args).freeze        #         @_memoized_mime_type[args] = _unmemoized_mime_type(*args).freeze\nend                                                                #       end\nelse                                                                 #     else\n\#{original_method}(*args)                                          #       _unmemoized_mime_type(*args)\nend                                                                  #     end\nend                                                                    #   end\nend                                                                      # end\n#\nif private_method_defined?(\#{original_method.inspect})                   # if private_method_defined?(:_unmemoized_mime_type)\nprivate \#{symbol.inspect}                                              #   private :mime_type\nend                                                                      # end\n", __FILE__, __LINE__ + 1
      end
    end

3Notes

Need to extend class when using this

MGPalmer · Dec 12, 20112 thanks

I had to dig around to find this out - if you want to use memoize somewhere, like an ActiveRecord model, you need to add

extend ActiveSupport::Memoizable

to the class. This doesn't seem to be explained anywhere (the only docs are 3 year old blog posts anyway).

this has been deprecated; replace with Memoist

roryokane · Jul 9, 2012

In Rails 3.2, memoize has been deprecated. In edge Rails, it has been removed.

The commit when it was deprecated: http://github.com/rails/rails/commit/36253916b0b788d6ded56669d37c96ed05c92c5c

A Stack Overflow question about this change: http://stackoverflow.com/q/9132197/578288

I personally disagree with the removal of memoize, and don’t recommend using the ||= pattern Rails now suggests. The exception is if your entire program only memoizes something once or twice, so it’s not worth including a gem for.

The easiest way to keep using memoize is to use the Memoist gem (http://github.com/matthewrudy/memoist , http://rubygems.org/gems/memoist), which is a simple extraction of ActiveSupport::Memoizable into its own gem.

instead of memoize

azhao · Nov 10, 2015

See this for deprecated https://github.com/rails/rails/commit/36253916b0b788d6ded56669d37c96ed05c92c5c

use 

def something
return @_var if defined? @_var
# more code
end