try_scope #2

try_scope.rb

class Object
  def try_scope(&block)
    block.call(self)
  rescue NoMethodError => e
    # Is there better ways than doing grep of the error message?
    if e.message.grep(/NilClass/).empty?
     raise 
    else
     nil
    end
  end
end

require "test/unit"

class TestTryScope < Test::Unit::TestCase
  def test_should_return_nil_when_nil_calls_a_method
    assert_nil(nil.try_scope{|a| a.foo})
  end
  
  def test_should_return_nil_when_nil_calls_chained_methods
    assert_nil(nil.try_scope{|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_nil(['1', nil].try_scope{|a| a.map{|b| b.upcase}.map{|b| b.downcase}})
  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".try_scope{|a| a.capitalize.nilme.downcase})
  end
  
  def test_should_raise_error_if_non_nil_value_calls_undefined_method
    assert_raise(NoMethodError) do
       ['a', 'b', 'c'].try_scope{|a| a.map{|b| b.capitalize}.map{|b| b.foo(1)}}
    end
  end
end