Addresses issue

Addresses issue #113. Allows specification of a proc, block, or sym for default values.

README.md

@@ -167,6 +167,62 @@ class Task
 end
 ```
 
+A note on defaults, you can specify a proc, block or symbol for your default if you want to get fancy. The most obvious use case for this  is that Ruby will optimize the assignment of an array so that a default of `[]` always points to the same object. Not exactly what is intended. Wrapping this in a proc causes a new array to be created. Here's an example:
+
+```
+class Foo
+  include MotionModel::Model
+  include MotionModel::ArrayModelAdapter
+  columns  subject: { type: :array, default: ->{ [] } }
+end
+```
+
+This is not constrained to initializing arrays. You can
+initialize pretty much anything using a proc or block.
+If you are specifying a block, make sure to use begin/end
+instead of do/end because it makes Ruby happy.
+
+Here's a different example:
+
+```
+class Timely
+  include MotionModel::Model
+  include MotionModel::ArrayModelAdapter
+  columns  ended_run_at: { type: :time, default: ->{ Time.now } }
+end
+```
+Note that this uses the "stubby proc" syntax. That is pretty much equivalent
+to:
+
+```
+columns  ended_run_at: { type: :time, default: lambda { Time.now } }
+```
+
+for the previous example.
+
+If you want to use a block, use the begin/end syntax:
+
+```
+columns  ended_run_at: { type: :time, default:
+  begin
+    Time.now
+  end
+  }
+```
+Finally, you can have the default call some class method as follows:
+
+```
+class Timely
+  include MotionModel::Model
+  include MotionModel::ArrayModelAdapter
+  columns  unique_thingie: { type: :integer, default: :randomize }
+
+  def self.randomize
+    rand 1_000_000
+  end
+end
+```
+
 You can also include the `Validatable` module to get field validation. For example:
 
 ```ruby

motion/model/model.rb

@@ -785,8 +785,40 @@ def rebuild_relation(col, instance_or_collection, options = {}) # nodoc
     def unload_relation(col)
     end
 
+    def evaluate_default_value(column, value)
+      default = self.class.default(column)
+
+      case default
+      when NilClass
+        {column => value}
+      when Proc
+        {column => default.call}
+      when Symbol
+        {column => self.send(column)}
+      else
+        {column => default}
+      end
+    end
+
+    # issue #113. added ability to specify a proc or block
+    # for the default value. This allows for arrays to be
+    # created as unique. E.g.:
+    #
+    #     class Foo
+    #       include MotionModel::Model
+    #       include MotionModel::ArrayModelAdapter
+    #       columns  subject: { type: :array, default: ->{ [] } }
+    #     end
+    #
+    #     ...
+    #
+    # This is not constrained to initializing arrays. You can
+    # initialize pretty much anything using a proc or block.
+    # If you are specifying a block, make sure to use begin/end
+    # instead of do/end because it makes Ruby happy.
+
     def initialize_data_columns(column, value) #nodoc
-      self.attributes = {column => value || self.class.default(column)}
+      self.attributes = evaluate_default_value(column, value)
     end
 
     def column_as(col) #nodoc

motion/version.rb

@@ -4,5 +4,5 @@
 # or forward port their code to take advantage
 # of adapters.
 module MotionModel
-  VERSION = "0.5.2"
+  VERSION = "0.5.3"
 end

spec/proc_defaults_spec.rb

@@ -0,0 +1,78 @@
+describe "proc for defaults" do
+  describe "accepts a proc or block for default" do
+    describe "accepts proc" do
+      class AcceptsProc
+        include MotionModel::Model
+        include MotionModel::ArrayModelAdapter
+        columns  subject: { type: :array, default: ->{ [] } }
+      end
+
+      before do
+        @test1 = AcceptsProc.create
+        @test2 = AcceptsProc.create
+      end
+
+      it "initializes array type using proc call" do
+        @test1.subject.should.be == @test2.subject
+      end
+    end
+
+    describe "accepts block" do
+      class AcceptsBlock
+        include MotionModel::Model
+        include MotionModel::ArrayModelAdapter
+        columns  subject: {
+          type: :array, default: begin
+            []
+          end
+        }
+      end
+
+      before do
+        @test1 = AcceptsBlock.create
+        @test2 = AcceptsBlock.create
+      end
+
+      it "initializes array type using begin/end block call" do
+        @test1.subject.should.be == @test2.subject
+      end
+    end
+
+    describe "accepts symbol" do
+      class AcceptsSym
+        include MotionModel::Model
+        include MotionModel::ArrayModelAdapter
+        columns  subject: { type: :integer, default: :randomize }
+
+        def self.randomize
+          rand 1_000_000
+        end
+      end
+
+      before do
+        @test1 = AcceptsSym.create
+        @test2 = AcceptsSym.create
+      end
+
+      it "initializes column by calling a method" do
+        @test1.subject.should.be == @test2.subject
+      end
+    end
+
+    describe "scalar defaults still work" do
+      class AcceptsScalars
+        include MotionModel::Model
+        include MotionModel::ArrayModelAdapter
+        columns  subject: { type: :integer, default: 42 }
+      end
+
+      before do
+        @test1 = AcceptsScalars.create
+      end
+
+      it "initializes column as normal" do
+        @test1.subject.should == 42
+      end
+    end
+  end
+end