Allow exporting a normal, not-indifferent Hash

Following the conventions in `activesupport` and the semantics of the
`#to_hash` method in Ruby's standard library, the `#to_hash` method for
a hash that has mixed in `IndifferentAccess` will now export the hash as
a normal, not-indifferent hash.

CHANGELOG.md

@@ -15,6 +15,7 @@ Any violations of this scheme are considered to be bugs.
 * [#523](https://github.com/hashie/hashie/pull/523): Added TOC, ensure a keep-a-changelog formatted CHANGELOG - [@dblock](https://github.com/dblock).
 * [#522](https://github.com/hashie/hashie/pull/522): Added eierlegende Wollmilchsau mascot graphic - [@carolineartz](https://github.com/carolineartz).
 * [#530](https://github.com/hashie/hashie/pull/530): Added Hashie::Extensions::Dash::PredefinedValues - [@caalberts](https://github.com/caalberts).
+* [#536](https://github.com/hashie/hashie/pull/536): Added exporting a normal Hash from an indifferent one through the `#to_hash` method - [@michaelherold](https://github.com/michaelherold).
 * Your contribution here.
 
 ### Changed

README.md

@@ -333,6 +333,18 @@ myhash['fishes'][:food] = 'flakes'
 myhash['fishes']['food'] # => "flakes"
 ```
 
+To get back a normal, not-indifferent Hash, you can use `#to_hash` on the indifferent hash. It exports the keys as strings, not symbols:
+
+```ruby
+myhash = MyHash.new
+myhash["foo"] = "bar"
+myhash[:foo]  #=> "bar"
+
+normal_hash = myhash.to_hash
+myhash["foo"]  #=> "bar"
+myhash[:foo]  #=> nil
+```
+
 ### IgnoreUndeclared
 
 This extension can be mixed in to silently ignore undeclared properties on initialization instead of raising an error. This is useful when using a Trash to capture a subset of a larger hash.

lib/hashie/extensions/indifferent_access.rb

@@ -143,6 +143,18 @@ module Hashie
         super.convert!
       end
 
+      def to_hash
+        {}.tap do |result|
+          each_pair { |key, value| result[key] = value }
+
+          if default_proc
+            result.default_proc = default_proc
+          else
+            result.default = default
+          end
+        end
+      end
+
       with_minimum_ruby('2.5.0') do
         def slice(*keys)
           string_keys = keys.map { |key| convert_key(key) }

spec/hashie/extensions/indifferent_access_spec.rb

@@ -77,6 +77,36 @@ describe Hashie::Extensions::IndifferentAccess do
     end
   end
 
+  describe '#to_hash' do
+    let(:indifferent_hash) { Class.new(::Hash) { include Hashie::Extensions::IndifferentAccess } }
+
+    it 'returns a normal hash without indifference' do
+      indifferent = indifferent_hash.new
+      indifferent['cat'] = 'meow'
+
+      subject = indifferent.to_hash
+
+      expect(subject['cat']).to eq 'meow'
+      expect(subject[:cat]).to be_nil
+    end
+
+    it 'maintains the #default_proc when set' do
+      indifferent = indifferent_hash.new { |_hash, key| "Nothing here: #{key}" }
+
+      subject = indifferent.to_hash
+
+      expect(subject['babble']).to eq 'Nothing here: babble'
+    end
+
+    it 'maintains the #default when set' do
+      indifferent = indifferent_hash.new(0)
+
+      subject = indifferent.to_hash
+
+      expect(subject['babble']).to eq 0
+    end
+  end
+
   describe 'when included in dash' do
     let(:params) { { foo: 'bar' } }
     subject { IndifferentHashWithDash.new(params) }