From: Josh Cheek <josh.cheek@...>
Date: 2009-11-03T21:47:19+09:00
Subject: Re: Merging hashes using both symbols and strings as keys

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On Fri, Oct 30, 2009 at 11:10 AM, shenry <stuarthenry@gmail.com> wrote:

> I'm trying to merge to hashes, one using symbols as keys (the defined
> default values for my class) and the other using strings as keys
> (taken from the params hash).
>
> default = { :name => "Joe", :age => 50 }
>
> params = { "name" => "Bill" }
>
> new_hash = default.merge(params)
> >> { :name => "Joe", :age => 50, "name" => "Bill }
>
> What's the Ruby way to handle this so that it overwrites :name with
> "name"? Do I need to implement a stringify_keys or symbolize_keys
> method like in Rails? I'd like to avoid using strings as the keys in
> my default hash.
>
> Any help greatly appreciated.
>
> Stu
>
>
I decided that I wasn't happy with the tests, it should be able to access
the same object through either a string or a symbol (previously it just
turned everything into a symbol, then if you tried to access that object w/
the string, it would not find it).

So I overrode [] and has_key? also, and changed some of the tests.

Here is the updated version



# file: symbolize_keys.rb

module SymbolizeKeys

  # converts any current string keys to symbol keys
  def self.extended(hash)
    hash.each do |key,value|
      if key.is_a?(String)
        hash.delete key
        hash[key] = value #through overridden []=
      end
    end
  end

  #considers string keys and symbol keys to be the same
  def [](key)
    key = convert_key(key)
    super(key)
  end

  #considers string keys and symbol keys to be the same
  def has_key?(key)
    key = convert_key(key)
    super(key)
  end

  # assigns a new key/value pair
  # converts they key to a symbol if it is a string
  def []=(*args)
    args[0] = convert_key(args[0])
    super
  end

  # returns new hash which is the merge of self and other hashes
  # the returned hash will also be extended by SymbolizeKeys
  def merge(*other_hashes , &resolution_proc )
    merged = Hash.new.extend SymbolizeKeys
    merged.merge! self , *other_hashes , &resolution_proc
  end

  # merges the other hashes into self
  # if a proc is submitted , it's return will be the value for the key
  def merge!( *other_hashes , &resolution_proc )

    # default resolution: value of the other hash
    resolution_proc ||= proc{ |key,oldval,newval| newval }

    # merge each hash into self
    other_hashes.each do |hash|
      hash.each{ |k,v|
        # assign new k/v into self, resolving conflicts with resolution_proc
        self[k] = self.has_key?(k) ? resolution_proc[k.to_sym,self[k],v] : v
      }
    end

    self
  end

private

  def convert_key(key)
    key.is_a?(String) ? key.to_sym : key
  end

end


--------------------------------------------------


# file: symbolize_keys_test.rb

require 'test/unit'
require 'symbolize_keys'

# this method was written by Gregory Brown
# and comes from
http://github.com/sandal/rbp/blob/7db25d4873042c02eca7232ad18e2432f0db7cb8/testing/test_unit_extensions.rb
module Test::Unit
  # Used to fix a minor minitest/unit incompatibility in flexmock
  AssertionFailedError = Class.new(StandardError)

  class TestCase

    def self.must(name, &block)
      test_name = "test_#{name.gsub(/\s+/,'_')}".to_sym
      defined = instance_method(test_name) rescue false
      raise "#{test_name} is already defined in #{self}" if defined
      if block_given?
        define_method(test_name, &block)
      else
        define_method(test_name) do
          flunk "No implementation provided for #{name}"
        end
      end
    end

  end
end


class ExtendingWithSymbolizeKeysTest < Test::Unit::TestCase
  def setup
    @default = {
      :age                         => 50    ,
      'initially a string'         => 51    ,
      /neither string nor symbol/  => 52    ,
    }
    @default.extend SymbolizeKeys
  end

  must "convert string keys to symbols when extended" do
    assert_equal @default[:'initially a string'] , 51
  end

  must "sym/str keys can access through either, but only one key" do
    assert_equal @default[ 'initially a string'] , 51
    assert_equal @default[:'initially a string'] , 51
    assert_equal @default[:'initially a string'] , @default['initially a
string']
    assert_equal @default.size , 3
  end

  must "leave symbol keys as symbols" do
    assert_equal @default[:age] , 50
  end

  must 'leave non symbols / strings as they are' do
    assert_equal @default[/neither string nor symbol/] , 52
  end

end


class SettingKeysWithSymbolizeKeysTest < Test::Unit::TestCase
  def setup
    @default = Hash.new.extend SymbolizeKeys
  end

  must "enable access to strings through symbols" do
    @default['foo'] = 'bar'
    assert_equal @default[:foo]  , 'bar'
    assert_same  @default[:foo]  , @default['foo']
  end

  must "enable access to symbols through strings" do
    @default[:foo] = 'bar'
    assert_equal @default['foo'] , 'bar'
    assert_same  @default[:foo]  , @default['foo']
  end

  must 'leave non symbols / strings as they are' do
    @default[/foo/] = :bar
    assert_equal @default[/foo/] , :bar
  end

end


class MergingWithSymbolizeKeysTest < Test::Unit::TestCase
  def setup
    @default = {
      :name                        => 'Joe'     ,
      :age                         => 50        ,
      'initially a string'         => 51        ,
      /neither string nor symbol/  => 52        ,
      :'from default'              => :default  ,
    }
    @params1 = {
      :name             => 'Bill'    ,
      'alias'           => 'Billy'   ,
      :'from params1'   => :params1  ,
    }
    @params2 = {
      'name'            => 'Sam'               ,
      'alias'           => 'Sammy'             ,
      12                => 'favourite number'  ,
      :'from params2'   => :params2            ,
    }
    @default.extend SymbolizeKeys
  end

  must "retain new keys for merge" do
    merged = @default.merge(@params2)
    assert_equal merged[12] , 'favourite number'
  end

  must "retain new keys for merge!" do
    @default.merge!(@params2)
    assert_equal @default[12] , 'favourite number'
  end

  must "replace current values with new values for merge" do
    merged = @default.merge(@params1)
    assert_equal merged[:name] , 'Bill'
  end

  must "replace current values with new values for merge!" do
    @default.merge!(@params1)
    assert_equal @default[:name] , 'Bill'
  end

  must "not change original hash for merge" do
    @default.merge(@params1)
    assert_equal @default[:name] , 'Joe'
  end

  must "receive [key,oldval,newval] as params to block" do
    h1 = {:no_conflict_1 => 1 , :conflict => 2 }.extend(SymbolizeKeys)
    h2 = {:conflict => 3 , :no_conflict_2 => 4}
    resolution_proc_params = nil
    h1.merge(h2){ |*params| resolution_proc_params = params }
    assert_equal resolution_proc_params , [:conflict,2,3]
  end

  must "only invoke the resolution proc on conflicts" do
    conflict_count = 0
    conflicts = { :name => false , :alias => false }
    @params1.extend(SymbolizeKeys).merge(@params2) do |k,ov,nv|
      conflict_count += 1
      conflicts[k] = true
    end
    assert_equal conflict_count , 2
    assert       conflicts[:name]
    assert       conflicts[:alias]
  end

  must "replace resolve conflicts with block for merge" do
    merged = @default.merge(@params1){ |key,oldval,newval| oldval }
    assert_equal merged[:name] , 'Joe'

    merged = @default.merge(@params1){ |key,oldval,newval| newval }
    assert_equal merged[:name] , 'Bill'
  end

  must "replace resolve conflicts with block for merge!" do
    @default.merge!(@params1){ |key,oldval,newval| oldval }
    assert_equal @default[:name] , 'Joe'

    @default.merge!(@params1){ |key,oldval,newval| newval }
    assert_equal @default[:name] , 'Bill'
  end

  must "convert string keys to symbols for merge" do
    unique_keys = @default.keys.map{|k|k.to_s.to_sym} |
@params1.keys.map{|k|k.to_s.to_sym}
    merged = @default.merge(@params1)
    assert_equal merged['alias'] , 'Billy'
    assert_equal merged[ :alias] , 'Billy'
    assert_equal merged.size     , unique_keys.size
  end

  must "convert string keys to symbols for merge!" do
    unique_keys = @default.keys.map{|k|k.to_s.to_sym} |
@params1.keys.map{|k|k.to_s.to_sym}
    @default.merge!(@params1)
    assert_equal @default['alias'] , 'Billy'
    assert_equal @default[ :alias] , 'Billy'
    assert_equal @default.size     , unique_keys.size
  end

  must "merge with multiple hashes" do
    merged = @default.merge(@params1,@params2)
    assert_equal merged[:'from default'] , :default
    assert_equal merged[:'from params1'] , :params1
    assert_equal merged[:'from params2'] , :params2
  end

  must "merge! with multiple hashes" do
    @default.merge!(@params1,@params2)
    assert_equal @default[:'from default'] , :default
    assert_equal @default[:'from params1'] , :params1
    assert_equal @default[:'from params2'] , :params2
  end

  must "return object that is extended with SymbolizeKeys, for merge" do
    merged = @default.merge(@params1)
    assert_kind_of SymbolizeKeys , merged
  end

  must "not modify original hash, for merge" do
    original = @default.dup
    @default.merge(@params1,@params2)
    assert_equal original , @default
  end

end

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