CODEWITHSUNDEEP
ruby-on-railsrubygemsmetaprogramming
Matt Huggins
Matt Huggins

Reputation: 83299

Where are these "without" methods in Rails gems getting defined?

I've seen a few places where *_without_* methods are being referenced in gems, and I don't see where they're being defined. Here are two examples from the validationgroup and delayed_jobs gems.

  1. In validation_group.rb, there is a method add_with_validation_group that is defined that references add_without_validation_group on its last line; however, add_without_validation_group does not appear to be defined anywhere.

    def add_with_validation_group(attribute,
                              msg = @@default_error_messages[:invalid], *args,
                              &block)
  add_error = true
  if @base.validation_group_enabled?
    current_group = @base.current_validation_group
    found = ValidationGroup::Util.current_and_ancestors(@base.class).
      find do |klass|
        klasses = klass.validation_group_classes
        klasses[klass] && klasses[klass][current_group] &&
        klasses[klass][current_group].include?(attribute)
      end
    add_error = false unless found
  end
  add_without_validation_group(attribute, msg, *args,&block) if add_error
end

  2. In DelayedJob's message_sending.rb, dynamically passed method parameters are being called as #{method}_without_send_later. However, I only see where #{method}_with_send_later is being defined anywhere in this gem.

    def handle_asynchronously(method)
  without_name = "#{method}_without_send_later"
  define_method("#{method}_with_send_later") do |*args|
    send_later(without_name, *args)
  end
  alias_method_chain method, :send_later
end

So my belief is that there's some Rails magic I'm missing with these "without" methods. However, I can't seem to figure out what to search for in Google to answer the question on my own.

Upvotes: 0

Views: 117

Answers (1)

brad
brad

Reputation: 32355

that's what alias_method_chain is providing you.

Basically when you say

alias_method_chain :some_method, :feature

You are provided two methods:

some_method_with_feature
some_method_without_feature

What happens is that when the original some_method is called, it actually calls some_method_with_feature. Then you get a reference to some_method_without_feature which is your original method declaration (ie for fallback/default behavior). So, you'll want to define some_method_with_feature to actually do stuff, which, as I say, is called when you call some_method

Example:

def do_something
  "Do Something!!"
end

def do_something_with_upcase
  do_something_without_upcase.upcase
end

alias_method_chain :do_something, :upcase

do_something # => "DO SOMETHING!!"

See the documentation here:

Upvotes: 4

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