hashblock.rb

def Hash(*args, &block)
  if args.any?
    args[0]
  else
    Hash.from_block &block
  end
end

class Hash
  def self.from_block &block
    Hash[*BlockBuilder.build(&block)]
  end
  
  class BlockBuilder
    @@collected = []
    class << self
      def build(&block)
        instance_eval &block
        copy = @@collected.clone and @@collected.clear and return copy
      end

      def method_missing(method, *args)
        @@collected.concat [method.to_sym, args.first]
      end
    end
  end
end

# Hash.from_block do
#   apple 8
#   banana 2
#   carrot 6
# end
# => {:apple=>8, :banana=>2, :carrot=>6}

# specs
require 'rubygems'
require 'spec'

def test_hash(h)
  h.keys.should include :apple
  h[:apple].should == 8
  h.keys.should include :banana
  h[:banana].should == 2
  h.keys.should include :carrot
  h[:carrot].should == 6
end

describe Hash do
  it 'should create a hash from a block' do
    h = Hash.from_block do
      apple 8
      banana 2
      carrot 6
    end

    test_hash(h)
  end

  it 'should create a hash from a block Hash { } syntax' do
    h = Hash do
      apple 8
      banana 2
      carrot 6
    end

    test_hash(h)
  end

  it 'should create a hash from a block with succinct syntax' do
    h = Hash({ :apple => 8, :banana => 2, :carrot => 6 })
    test_hash(h)
  end

  it 'should not be necessary to even have this class at all' do
    h = { :apple => 8, :banana => 2, :carrot => 6 }
    test_hash(h)
  end

  it 'is even better in ruby 1.9' do
    h = { apple: 8, banana: 2, carrot: 6 }
    test_hash(h)
  end
end