maybe{}

maybe{}

# NOTE: This won't work as expected in threaded environment.
class Object
  def maybe(&block)
    that = self
    result = NilClass.class_eval do
      alias_method :orig_method_missing, :method_missing
      define_method :method_missing do
        nil
      end
      result = block.call(that)
      alias_method :method_missing, :orig_method_missing
      result
    end
  end
end

require "test/unit"

class TestTryScope < Test::Unit::TestCase
  def test_should_return_nil_when_nil_calls_a_method
    assert_nil(nil.maybe{|a| a.foo})
  end
  
  def test_should_return_nil_when_nil_calls_chained_methods
    assert_nil(nil.maybe{|a| a.map{|b| b.capitalize}.map{|b| b.downcase}})
  end
  
  def test_should_return_nil_when_an_array_with_nil_calls_chained_method
    assert_equal(
      ['A', nil], 
      ['a', nil].maybe do |a| 
        a.map(&:upcase).map(&:downcase).map(&:upcase)
      end  
    )
  end
  
  def test_should_return_nil_when_chained_method_returns_nil
    # Same as "class Object ; def nilme ; nil ; end ; end"
    Object.class_eval do
      define_method :nilme do
        nil
      end
    end
    assert_nil("foo".maybe{|a| a.capitalize.nilme.downcase.aa.bbb})
  end
  
  def test_should_raise_error_if_non_nil_value_calls_undefined_method
    assert_raise(NoMethodError) do
       ['a', 'b', 'c'].maybe{|a| a.map{|b| b.capitalize}.map{|b| b.foo(1)}}
    end
  end
end