reverse_merge!() modifies the hash outside the method scope

Hi,

I have a Hash that is passed as a method argument to several methods on different Models. It has to be the same when it enters each method, but each Model can apply some specific default values to the Hash with reverse_merge!()

I'm surprised to see that in fact each method call modifies the original Hash, the one that is outside the scope of each method.

I don't doubt that it's an absolutly normal behavior from a Ruby perspective, but I don't think it's normal from the Rails perspective. At least I didn't expect this.

I've written a small rake task to illustrate this :

desc "bug reverse_merge!"
task(:reverse_merge) do
  
  options = {
    :attr1 => "generic string"
  }
  
  def some_method(options = {})
    default_options = {
      :attr1 => "default string",
      :attr2 => "another string"
    }
    options.reverse_merge!(default_options)

    puts "*** options INSIDE the method call :"
    puts options.inspect
  end
  
  puts "*** options BEFORE the method call :"
  puts options.inspect
  
  some_method(options)
  
  puts "*** options AFTER the method call :"
  puts options.inspect
  
end