Added format filter to enforce formatting on array objects

src/cligen/command/argument.cr

@@ -41,6 +41,12 @@ module CliGen
         {% format = format.resolve if format.is_a? Path %}
         {% raise "ERROR : CliGen::Command.argument(#{name}) : Provided format must be a RegexLiteral" unless format.is_a? RegexLiteral %}
       {% end %}
+      {% if type.resolve <= Array && format.nil? %}
+        {% elem = type.type_vars.first %}
+        {% unless elem == Int32 %}
+          {% raise "ERROR : CliGen::Command.argument(#{name}) : When providing custom data types for Array(T) or using Array(String) you must provide a format for argument filtering so that parsing can be done deterministically" %}
+        {% end %}
+      {% end %}
 
       @[CliGen::Argument(short: {{short}}, long: {{long}}, description: {{description}}, validation: {{validation}}, on_match: {{on_match}}, options: {{options}}, delimiter: {{delimiter}}, format: {{format}})]
       @{{variable}}