added def_init

src/cligen/command.cr

@@ -6,12 +6,18 @@ require "./command/argument"
 require "./command/selection"
 require "./command/help_template"
 require "./command/subcommand"
+require "./command/def_init"
 
 module CliGen
   class Command
     macro inherited
       {% verbatim do %}
       macro finished
+        {% anno = @type.annotation(CliGen::CommandInfo) %}
+        {% raise "" unless anno %}
+        {% if anno[:def_init] %}
+          def_init
+        {% end %}
         def initialize(*, handler : CliGen::BaseCommandNode)
           {% verbatim do %}
             {% for var in @type.instance_vars %}

src/cligen/command/def_init.cr

@@ -0,0 +1,22 @@
+module CliGen
+  class Command
+    macro def_init
+      def initialize
+        {% verbatim do %}
+          {% for var in @type.instance_vars %}
+            {% raise "ERROR : Can't define a default initializer if #{var.name} doesn't have a default" if var.default_value.nil? && !var.type.nilable? %}
+            @{{var.name}} = {{var.default_value}}
+          {% end %}
+        {% end %}
+      end
+
+      def after_initialize
+        @@instance = self
+      end
+
+      def self.get 
+        @@instance ||= new
+      end
+    end
+  end
+end