Added step argument transformations

examples/self_test/features/step_definitions/sample_steps.rb

@@ -28,6 +28,7 @@ def flunker
   raise "We already have #{@cukes} cukes!" if @cukes
   @cukes = cukes
 end
+
 Then /^I should have '(.+)' cukes$/ do |cukes|
   @cukes.should == cukes
 end
@@ -79,3 +80,11 @@ def flunker
   FileUtils.mkdir_p(File.dirname(after_file))
   FileUtils.touch(after_file)
 end
+
+Then /^I should not transform ('\d+') to an Integer$/ do |string|
+  string.should be_kind_of(String)
+end
+
+Then /^I should transform ('\d+' to an Integer)$/ do |integer|
+  integer.should be_kind_of(Integer)
+end

examples/self_test/features/support/env.rb

@@ -16,3 +16,7 @@
 After('@background_tagged_before_on_outline') do
   @cukes.should == '888'
 end
+
+Cucumber::StepMother.register_transform /'\d+' to an Integer/ do |group|
+  /'(\d+)' to an Integer/.match(group)[0].to_i
+end

examples/self_test/features/transform_sample.feature

@@ -0,0 +1,7 @@
+Feature: Step argument transformations
+
+  Scenario: transform with matches
+    Then I should transform '10' to an Integer
+
+  Scenario: transform without matches
+    Then I should not transform '10' to an Integer

lib/cucumber/core_ext/instance_exec.rb

@@ -21,7 +21,7 @@ def cucumber_instance_exec(check_arity, pseudo_method, *args, &block)
           )
         end
       else
-        instance_exec(*args, &block)
+        instance_exec(*Cucumber::StepMother.transform_arguments(args), &block)
       end
     end
   end

lib/cucumber/step_mother.rb

@@ -50,8 +50,8 @@ def initialize(step_def_1, step_def_2)
 
   # This is the meaty part of Cucumber that ties everything together.
   class StepMother
-    include Constantize
-
+    include Constantize    
+    @@transforms = {}
     attr_writer :options, :visitor, :log
 
     def initialize
@@ -60,6 +60,21 @@ def initialize
       @language_map = {}
       load_natural_language('en')
     end
+
+    def self.register_transform(pattern, &transform)
+      raise 'Transform must be registered with a block' unless block_given?
+      @@transforms[pattern] = transform.to_proc
+    end
+
+    def self.transform_arguments(args)
+      args.map do |arg|
+        if pattern = @@transforms.keys.detect {|pattern| arg =~ pattern }
+          @@transforms[pattern].call(arg)
+        else
+          arg
+        end
+      end
+    end
 
     def load_plain_text_features(feature_files)
       features = Ast::Features.new