plugin method: use const_defined? about shrine

[janko]

Thanks for raising this concern. I definitely agree with you that const_defined? is better than defined?, I haven't thought about that. I will push a fix shortly.

[janko]

Now that I think about it more, this case would only happen if the plugin is defined on top-level (instead of under Shrine::Plugins which is the convention), and only if one of these constants are defined on top-level, which is extremely unlikely. And what you're proposing is changing from

def plugin(plugin, *args, &block)
  plugin = Plugins.load_plugin(plugin) if plugin.is_a?(Symbol)
  plugin.load_dependencies(self, *args, &block) if plugin.respond_to?(:load_dependencies)
  self.include(plugin::InstanceMethods) if defined?(plugin::InstanceMethods)
  self.extend(plugin::ClassMethods) if defined?(plugin::ClassMethods)
  self::UploadedFile.include(plugin::FileMethods) if defined?(plugin::FileMethods)
  self::UploadedFile.extend(plugin::FileClassMethods) if defined?(plugin::FileClassMethods)
  self::Attachment.include(plugin::AttachmentMethods) if defined?(plugin::AttachmentMethods)
  self::Attachment.extend(plugin::AttachmentClassMethods) if defined?(plugin::AttachmentClassMethods)
  self::Attacher.include(plugin::AttacherMethods) if defined?(plugin::AttacherMethods)
  self::Attacher.extend(plugin::AttacherClassMethods) if defined?(plugin::AttacherClassMethods)
  plugin.configure(self, *args, &block) if plugin.respond_to?(:configure)
  nil
end

to

def plugin(plugin, *args, &block)
  plugin = Plugins.load_plugin(plugin) if plugin.is_a?(Symbol)
  plugin.load_dependencies(self, *args, &block) if plugin.respond_to?(:load_dependencies)
  self.include(plugin::InstanceMethods) if plugin.const_defined?(:InstanceMethods, false)
  self.extend(plugin::ClassMethods) if plugin.const_defined?(:ClassMethods, false)
  self::UploadedFile.include(plugin::FileMethods) if plugin.const_defined?(:FileMethods, false)
  self::UploadedFile.extend(plugin::FileClassMethods) if plugin.const_defined?(:FileClassMethods, false)
  self::Attachment.include(plugin::AttachmentMethods) if plugin.const_defined?(:AttachmentMethods, false)
  self::Attachment.extend(plugin::AttachmentClassMethods) if plugin.const_defined?(:AttachmentClassMethods, false)
  self::Attacher.include(plugin::AttacherMethods) if plugin.const_defined?(:AttacherMethods, false)
  self::Attacher.extend(plugin::AttacherClassMethods) if plugin.const_defined?(:AttacherClassMethods, false)
  plugin.configure(self, *args, &block) if plugin.respond_to?(:configure)
  nil
end

The const_defined? syntax is much more unreadable to me, especially with the second argument, and for the reasons stated I don't think it's worth the tradeoff.