Replace boilerplate Ruby `def initialize` followed by instance variable settings with `initialize_vars` specifying variables once

initialize_vars.rb

# XXX This worked in 2009 with Ruby 1.8; I've not tested on anything
# more recent. But you get the general idea.

class Class

    def initialize_vars(*vars, &initialize_block)
        vars.each { |arg| attr_reader arg.to_sym }
        varsyms = vars.collect { |arg| ('@' + arg.to_s).to_sym }
        define_method(:initialize) { |*init_args|
            raise(ArgumentError, "wrong number of arguments " +
                "(#{init_args.length} for #{vars.length})") unless
                vars.length == init_args.length
            vars.zip(init_args).each { |var, arg|
                instance_variable_set(('@' + var.to_s).to_sym, arg)
            }
            self.instance_eval(&initialize_block) if initialize_block
        }
    end

end

initialize_vars.rt

class TC_RubyExtensions < Test::Unit::TestCase

    class TestInitializeVarsSimple
        initialize_vars :a
    end

    def test_initialize_vars_simple
        obj = TestInitializeVarsSimple.new('abc')
        assert_equal('abc', obj.a)
        assert_raise(NoMethodError) { obj.a = 'def' }
    end

    class TestInitializeVarsWithInitBlock
        initialize_vars(:foo, :bar) do
            @baz = bar * 3
        end
        attr_writer :bar
        attr_reader :baz
    end

    def test_initialize_vars_with_init_block
        obj = TestInitializeVarsWithInitBlock.new(1, 2)
        assert_equal(1, obj.foo)
        assert_equal(2, obj.bar)
        assert_equal(6, obj.baz)
        assert_raise(NoMethodError) { obj.foo = 1 }
        obj.bar = 3; assert_equal(3, obj.bar)
    end

    def test_initialize_vars_wrong_number_of_args
        klass = TestInitializeVarsWithInitBlock

        e = assert_raise(ArgumentError) { klass.new }
        assert_equal('wrong number of arguments (0 for 2)', e.message)

        e = assert_raise(ArgumentError) { klass.new(1) }
        assert_equal('wrong number of arguments (1 for 2)', e.message)

        e = assert_raise(ArgumentError) { klass.new(1, 2, 3) }
        assert_equal('wrong number of arguments (3 for 2)', e.message)
    end

end