Add an extension to maintain original Mash keys

One of the behaviors of Mash that we see regularly surprise users is
that Mash stringifies any keys passed into it. This leads to unexpected
lack of synergy between Mash and its cousins (particularly Dash), since
the property DSLs do not handle indifferent key access.

This extension ensures that the original keys are kept inside the Mash's
data structure, at the expense of more costly logic for fetching
information indifferently. I have included a benchmark that compares the
two. The benchmark shows that when you are passing string keys into a
Mash, using this extension will actually be _faster_ than the default
implementation, but that the reverse is true when passing symbol keys.

In hashie#296, I tried to do this universally for all Mashes, which slowed
down the fetching behavior for Mash significantly. I like this attempt
much better because it allows users to opt into the new behavior if they
want it, while still keeping the default implementation as-is.

Fixes hashie#196 by giving the option of keeping the original structure of the
Mash when using it with Dash.

Fixes hashie#246 by giving the option of opting into keeping the original
keys.

Closes hashie#296 by giving a more flexible path forward that doesn't change
the semantics of the main Mash class.

CHANGELOG.md

@@ -12,6 +12,7 @@ scheme are considered to be bugs.
 
 ### Added
 
+* [#326](https://github.com/intridea/hashie/pull/326): Added `Hashie::Extensions::Mash::MaintainOriginalKeys` to give Mashes the ability to keep the original structure given to it - [@michaelherold](https://github.com/michaelherold).
 * Your contribution here.
 
 ### Changed

Gemfile

@@ -3,6 +3,7 @@ source 'http://rubygems.org'
 gemspec
 
 group :development do
+  gem 'benchmark-ips'
   gem 'pry'
   gem 'pry-stack_explorer', platforms: [:ruby_19, :ruby_20, :ruby_21]
   gem 'rubocop', '0.34.2'

README.md

@@ -545,6 +545,25 @@ class Response < Hashie::Mash
 end
 ```
 
+### Mash Extension: KeepOriginalKeys
+
+This extension can be mixed into a Mash to keep the form of any keys passed directly into the Mash. By default, Mash converts keys to strings to give indifferent access. This extension still allows indifferent access, but keeps the form of the keys to eliminate confusion when you're not expecting the keys to change.
+
+```ruby
+class KeepingMash < ::Hashie::Mash
+  include Hashie::Extensions::Mash::KeepOriginalKeys
+end
+
+mash = KeepingMash.new(:symbol_key => :symbol, 'string_key' => 'string')
+mash.to_hash == { :symbol_key => :symbol, 'string_key' => 'string' }  #=> true
+mash.symbol_key  #=> :symbol
+mash[:symbol_key]  #=> :symbol
+mash['symbol_key']  #=> :symbol
+mash.string_key  #=> 'string'
+mash['string_key']  #=> 'string'
+mash[:string_key]  #=> 'string'
+```
+
 ### Mash Extension: SafeAssignment
 
 This extension can be mixed into a Mash to guard the attempted overwriting of methods by property setters. When mixed in, the Mash will raise an `ArgumentError` if you attempt to write a property with the same name as an existing method.

benchmarks/keep_original_mash_keys.rb

@@ -0,0 +1,28 @@
+require_relative '../lib/hashie'
+require 'benchmark/ips'
+
+class KeepingMash < Hashie::Mash
+  include Hashie::Extensions::Mash::KeepOriginalKeys
+end
+
+original = { test: 'value' }
+mash = Hashie::Mash.new(original)
+keeping_mash = KeepingMash.new(original)
+
+Benchmark.ips do |x|
+  x.report('keep symbol') { keeping_mash.test }
+  x.report('normal symbol') { mash.test }
+
+  x.compare!
+end
+
+original = { 'test' => 'value' }
+mash = Hashie::Mash.new(original)
+keeping_mash = KeepingMash.new(original)
+
+Benchmark.ips do |x|
+  x.report('keep string') { keeping_mash.test }
+  x.report('normal string') { mash.test }
+
+  x.compare!
+end

lib/hashie.rb

@@ -44,6 +44,7 @@ module Dash
     end
 
     module Mash
+      autoload :KeepOriginalKeys, 'hashie/extensions/mash/keep_original_keys'
       autoload :SafeAssignment, 'hashie/extensions/mash/safe_assignment'
       autoload :SymbolizeKeys, 'hashie/extensions/mash/symbolize_keys'
     end

lib/hashie/extensions/mash/keep_original_keys.rb

@@ -0,0 +1,54 @@
+module Hashie
+  module Extensions
+    module Mash
+      # Overrides the indifferent access of a Mash to keep keys in the
+      # original format given to the Mash.
+      #
+      # @example
+      #   class KeepingMash < Hashie::Mash
+      #     include Hashie::Extensions::Mash::KeepOriginalKeys
+      #   end
+      #
+      #   mash = KeepingMash.new(:symbol_key => :symbol, 'string_key' => 'string')
+      #   mash.to_hash  #=> { :symbol_key => :symbol, 'string_key' => 'string' }
+      #   mash['string_key'] == mash[:string_key]  #=> true
+      #   mash[:symbol_key] == mash['symbol_key']  #=> true
+      module KeepOriginalKeys
+        private
+
+        def self.included(descendant)
+          unless descendant <= Hashie::Mash
+            fail ArgumentError, "#{descendant} is not a kind of Hashie::Mash"
+          end
+        end
+
+        # Converts the key when necessary to access the correct Mash key.
+        #
+        # @param [Object, String, Symbol] key the key to access.
+        # @return [Object] the value assigned to the key.
+        def convert_key(key)
+          if regular_key?(key)
+            key
+          elsif (converted_key = __convert(key)) && regular_key?(converted_key)
+            converted_key
+          else
+            key
+          end
+        end
+
+        # Converts symbol/string keys to their alternative formats, but leaves
+        # other keys alone.
+        #
+        # @param [Object, String, Symbol] key the key to convert.
+        # @return [Object, String, Symbol] the converted key.
+        def __convert(key)
+          case key
+          when Symbol then key.to_s
+          when String then key.to_sym
+          else key
+          end
+        end
+      end
+    end
+  end
+end

lib/hashie/mash.rb

@@ -189,6 +189,7 @@ def dup
       self.class.new(self, default)
     end
 
+    alias_method :regular_key?, :key?
     def key?(key)
       super(convert_key(key))
     end

spec/hashie/dash_spec.rb

@@ -192,6 +192,32 @@ class DashMessageOptionWithoutRequiredTest < Hashie::Dash
     end
   end
 
+  context 'converting from a Mash' do
+    class ConvertingFromMash < Hashie::Dash
+      property :property, required: true
+    end
+
+    context 'without keeping the original keys' do
+      let(:mash) { Hashie::Mash.new(property: 'test') }
+
+      it 'does not pick up the property from the stringified key' do
+        expect { ConvertingFromMash.new(mash) }.to raise_error(NoMethodError)
+      end
+    end
+
+    context 'when keeping the original keys' do
+      class KeepingMash < Hashie::Mash
+        include Hashie::Extensions::Mash::KeepOriginalKeys
+      end
+
+      let(:mash) { KeepingMash.new(property: 'test') }
+
+      it 'picks up the property from the original key' do
+        expect { ConvertingFromMash.new(mash) }.not_to raise_error
+      end
+    end
+  end
+
   describe '#new' do
     it 'fails with non-existent properties' do
       expect { described_class.new(bork: '') }.to raise_error(*no_property_error('bork'))

spec/hashie/extensions/mash/keep_original_keys_spec.rb

@@ -0,0 +1,46 @@
+require 'spec_helper'
+
+RSpec.describe Hashie::Extensions::Mash::KeepOriginalKeys do
+  let(:keeping_mash) do
+    Class.new(Hashie::Mash) do
+      include Hashie::Extensions::Mash::KeepOriginalKeys
+    end
+  end
+
+  it 'keeps the keys in the resulting hash identical to the original' do
+    original = { :a => 'apple', 'b' => 'bottle' }
+    mash = keeping_mash.new(original)
+
+    expect(mash.to_hash).to eq(original)
+  end
+
+  it 'indifferently responds to keys' do
+    original = { :a => 'apple', 'b' => 'bottle' }
+    mash = keeping_mash.new(original)
+
+    expect(mash['a']).to eq(mash[:a])
+    expect(mash['b']).to eq(mash[:b])
+  end
+
+  it 'responds to all method accessors like a Mash' do
+    original = { :a => 'apple', 'b' => 'bottle' }
+    mash = keeping_mash.new(original)
+
+    expect(mash.a).to eq('apple')
+    expect(mash.a?).to eq(true)
+    expect(mash.b).to eq('bottle')
+    expect(mash.b?).to eq(true)
+    expect(mash.underbang_).to be_a(keeping_mash)
+    expect(mash.bang!).to be_a(keeping_mash)
+    expect(mash.predicate?).to eq(false)
+  end
+
+  it 'keeps the keys that are directly passed without converting them' do
+    original = { :a => 'apple', 'b' => 'bottle' }
+    mash = keeping_mash.new(original)
+
+    mash[:c] = 'cat'
+    mash['d'] = 'dog'
+    expect(mash.to_hash).to eq(:a => 'apple', 'b' => 'bottle', :c => 'cat', 'd' => 'dog')
+  end
+end