gistfile1.rb

require 'rubygems'
require 'thor'
require 'active_support/core_ext/hash'

h1 = {:a => 1}
# => {:a=>1} 

h2 = Thor::CoreExt::HashWithIndifferentAccess.new(:a => 2)
# => {"a"=>2} 

h3 = ActiveSupport::HashWithIndifferentAccess.new(:a => 3)
# => {"a"=>3}

h1.merge(h2)
# => {:a=>1, "a"=>2}

h1.merge(h3)
# => {:a=>1, "a"=>3}

h2.reverse_merge :a => 13
# => {:a=>13, "a"=>2}

h3.reverse_merge :a => 13
# => {"a"=>3}

def method1(opts={})
  opts = {
    :default => :options,
    :are => :not_merged
  }.merge(opts)
end

opts = {:default => :choices, :are => :merged}
thor_opts = Thor::CoreExt::HashWithIndifferentAccess.new(:default => :choices, :are => :string_indexed_and_merged)
as_opts = ActiveSupport::HashWithIndifferentAccess.new(:default => :choices, :are => :string_indexed_and_merged)

method1(opts)
# => {:default=>:choices, :are=>:merged}

method1(thor_opts)
# => {:default=>:options, :are=>:not_merged, "default"=>:choices, "are"=>:string_indexed_and_merged}

method1(as_opts)
# => {:default=>:options, :are=>:not_merged, "default"=>:choices, "are"=>:string_indexed_and_merged}

### Working with the usual default_options_hash.merge(user_options) won't work with neither HashWithIndifferentAccess versions. #symbolize_keys works on AS version, though:

# Thor version won't work

thor_opts.symbolize_keys
# => {"default"=>:choices, "are"=>:string_indexed_and_merged}

method1(thor_opts.symbolize_keys)
# => {:default=>:options, :are=>:not_merged, "default"=>:choices, "are"=>:string_indexed_and_merged}

# AS version works

as_opts.symbolize_keys
# => {:default=>:choices, :are=>:merged}

method1(as_opts.symbolize_keys)
# => {:default=>:choices, :are=>:merged} 


### Now a second method using ActiveSupport's #reverse_merge

def method2(opts={})
  opts = opts.reverse_merge :default => :options, :are => :not_merged
end

opts = {:default => :choices, :are => :reverse_merged}
thor_opts = Thor::CoreExt::HashWithIndifferentAccess.new(:default => :choices, :are => :string_indexed_and_reverse_merged)
as_opts = ActiveSupport::HashWithIndifferentAccess.new(:default => :choices, :are => :reverse_merged)

method2(opts)
# => {"default"=>:choices, "are"=>:reverse_merged}

method2(thor_opts)
# => {:default=>:options, :are=>:not_merged, "default"=>:choices, "are"=>:string_indexed_and_reverse_merged}

method2(as_opts)
# => {"default"=>:choices, "are"=>:reverse_merged}