Question

I was trying to do an open source contribution, and the line of code in the star_rating method below with options.merge() (this is the change I tried to submit) was kicked back with the following message “This is invalid Ruby syntax (in both 1.8.7 and 1.9.3)…” My question is why? I checked the Hash#merge method on the ruby interactive shell and it seems to work.

def star_rating(options = {})
   ##original line of code
   has_many :rates_without_dimension, :as => :rateable, :class_name => 'RateMe', :dependent => :destroy, :conditions => {:dimension => nil}  

  ##line of code I tried to submit
  has_many :rates_without_dimension, :as => :rateable, options.merge(:class_name => 'RateMe'), :dependent => :destroy, :conditions => {:dimension => nil}  
end

Answer 1

This is indeed invalid syntax. The last arguments of a method call can be a Hash, in which case Ruby allows you to drop the enclosing {}:

foo(1, 2, 3, :a => 4, :b => 5)
# equivalent to:
foo(1, 2, 3, {:a => 4, :b => 5})

In your case, you have :as => :rateable before a simple argument (options.merge), that’s not allowed.

If you inverted them, you still wouldn’t get the effect you want:

has_many :rates_without_dimension, options.merge(:class_name => 'RateMe'), :as => :rateable, :dependent => :destroy, :conditions => {:dimension => nil}
# same as
has_many :rates_without_dimension, options.merge(:class_name => 'RateMe'), {:as => :rateable, :dependent => :destroy, :conditions => {:dimension => nil}}
# => has 3 arguments, not 2.

What you can do here is insure you are passing two parameters. One way to do this:

has_many :rates_without_dimension, options.merge(:class_name => 'RateMe', :as => :rateable, :dependent => :destroy, :conditions => {:dimension => nil})

Note that in Ruby 2.0, it will be possible to do what you wanted using the equivalent of the splat operators for arrays (*) which will be ** for hashes:

h = {:b => 2}
foo(:a => 1, **h, :c => 3)
# same as
foo(:a => 1, :b => 2, :c => 3) 

# so you will be allowed to write:
has_many :rates_without_dimension, :as => :rateable, **options.merge(:class_name => 'RateMe'), :dependent => :destroy, :conditions => {:dimension => nil}