creating shared branches for our trees

Signed-off-by: Ryan Allen <ryan@yeahnah.org>

lumberjack.rb

@@ -5,7 +5,8 @@ def self.construct(initial_scope = [], &block)
     builder.__process(block)    
   end
 
-  @@methods_to_keep = /^__/, /class/, /instance_eval/, /method_missing/
+  @@methods_to_keep = /^__/, /class/, /instance_eval/, /method_missing/,
+                      /instance_variable_(g|s)et/
 
   instance_methods.each do |m|
     undef_method m unless @@methods_to_keep.find { |r| r.match m }
@@ -34,6 +35,16 @@ def load_tree_file(filename)
     end
   end
 
+  def shared_branch(branch_name, &block)
+    instance_variable_set "@#{branch_name}", lambda(&block)
+  end
+
+  def graft_branch(branch_name)
+    branch = instance_variable_get("@#{branch_name}")
+    raise "Attemption to graft branch #{branch_name} which is undefined" unless branch
+    instance_eval(&branch)
+  end
+
   def method_missing(*args, &block)
     # if we only have one arg, and no block, then we're trying to build a
     # module scope, i.e. a/b/c/d would resolve to A::B::C::D, so let's start

lumberjack_test.rb

@@ -240,4 +240,52 @@ def test_we_can_load_in_other_files
     assert_equal 10, family.first.members.last.age
 
   end
+
+  def test_we_can_share_branches_that_are_defined
+    families = Lumberjack.construct do
+
+      shared_branch :kids do
+        person 'Jack', 11
+        person 'Jill', 10
+      end
+
+      family "Dad's new family" do
+        members do
+          person 'Dad', 45
+          graft_branch :kids
+        end
+      end
+
+      family "Mum's new family" do
+        members do
+          person 'Mum', 40
+          person 'Red-headed step-child', 8
+          graft_branch :kids
+        end
+      end
+    end
+
+    assert 2, families.length
+    assert_kind_of Family, families[0]
+    assert_kind_of Family, families[1]
+
+    assert 3, families[0].members.size
+    assert families[0].members.any? {|m| m.given_name == 'Jack'}
+    assert families[0].members.any? {|m| m.given_name == 'Jill'}
+
+    assert 4, families[1].members.size
+    assert families[1].members.any? {|m| m.given_name == 'Jack'}
+    assert families[1].members.any? {|m| m.given_name == 'Jill'}
+  end
+
+  def test_we_cant_share_branches_that_are_undefined
+    # TODO: why does this output funny stuff
+    assert_raise RuntimeError do
+      Lumberjack.construct do
+        family 'wont work' do
+            graft_branch :non_existant
+        end
+      end
+    end
+  end
 end