pmarreck · August 30, 2012 15:36 · Aug 30, 2012
diff --git a/ruby_object_quick_initialization.rb b/ruby_object_quick_initialization.rb
@@ -0,0 +1,70 @@
+
+# Some code that lets you quickly erect objects and their attributes with a params hash
+
+class InvalidAutoInitializeParamError < StandardError; end
+
+class Object
+  class << self
+    alias new_without_auto_initialize new
+    def new_with_auto_initialize(*args,&block)
+      a1 = args.first
+      o = new_without_auto_initialize
+      if a1.class==Hash
+        if o.respond_to?(:initialize_with_hash)
+          a1.keys.each do |k|
+            setter = (k.to_s << '=').to_sym
+            if o.respond_to? k || o.respond_to?(setter) # for now, only allow keys that have accessors
+              if o.respond_to?(setter)
+                o.send(setter, a1[k])
+              else
+                o.instance_variable_set("@#{k}".to_sym, a1[k])
+              end
+            else # don't allow it
+              raise InvalidAutoInitializeParamError, "The auto initialize parameter '#{k}' is not allowed for this object"
+            end
+          end
+          if o.method(:initialize_with_hash).arity >= 1
+            o.initialize_with_hash(*args, &block)
+          else
+            o.initialize_with_hash(&block)
+            yield o if block_given?
+          end
+        end
+      end
+      o
+    end
+    alias new new_with_auto_initialize
+  end
+end
+
+class Class
+  def initialize_with_hash
+    self.send(:define_method, :initialize_with_hash){}
+  end
+end
+
+class A
+  attr_reader :this, :that
+  def initialize_with_hash
+    p instance_variables
+  end
+end
+
+class B
+  attr_accessor :whoa_dude
+  initialize_with_hash
+end
+
+a = A.new({this: 5, that: 10}){ |a| p a }
+
+b = B.new(whoa_dude: 'yeah')
+
+p b
+
+#=> [:@this, :@that]
+#=> #<A:0x007ff6c2884698 @this=5, @that=10>
+#=> #<B:0x007ff6c2884288 @whoa_dude="yeah">
+
+a = A.new({this: 5, that: 10, those: 7})
+
+#=> The auto initialize parameter 'those' is not allowed for this object (InvalidAutoInitializeParamError)