CODEWITHSUNDEEP
rubydry
Steve Katz
Steve Katz

Reputation: 105

Avoid reppetitive respond_to? calling

I need to check whether a object respond to an arbitrary number of methods.

And i'm tired of doing this:

if a.respond_to?(:foo) && a.respond_to?(:bar) && a.respond_to?(:blah)

What would be a more "correct" DRY way to do this?

Upvotes: 0

Views: 371

Answers (4)

user904990
user904990

Reputation:

Try this if you have nothing against monkeypatching:

class Object
  def respond_to_all? *meths
    meths.all? { |m| self.respond_to?(m) }
  end

  def respond_to_any? *meths
    meths.any? { |m| self.respond_to?(m) }
  end
end

p 'a'.respond_to_all? :upcase, :downcase, :capitalize
#=> true

p 'a'.respond_to_all? :upcase, :downcase, :blah
#=> false

p 'a'.respond_to_any? :upcase, :downcase, :blah
#=> true

p 'a'.respond_to_any? :upcaze, :downcaze, :blah
#=> false

UPDATE: using meths.all? and meths.any?. @MarkThomas, thanks for refreshing my mind.

UPDATE: fixing responsd typo.

Upvotes: 2

Mark Thomas
Mark Thomas

Reputation: 37517

You can always wrap it in a helper method:

def has_methods?(obj, *methods)
   methods.all?{|method| obj.respond_to? method}
end

Upvotes: 3

Zach Kemp
Zach Kemp

Reputation: 11904

The 'correct' way (or one of many, anyway), is Tell Don't Ask, meaning that if you're sending the object a message, you expect it to respond without complaining. This is also known as Duck Typing (if it can quack, it's a duck).

I can't give you any specific advice, because you haven't asked a specific question. If you're testing for three different methods it seems like you don't know what kind of object a is, which can be an interesting case to deal with. Post more code!

Upvotes: 0

megas
megas

Reputation: 21791

Check the Active Support extension from Rails. It has method try. It's hard to say how you can use this method because of lack of context, maybe something like this:

if a.try(:foo) && a.try(:bar) && a.try(:blah)

In order to use this method you should 

require 'active_support/core_ext/object/try.rb'

Also check my version of this method the tryit:

Upvotes: 0

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