define_method vs module_eval

rubyonrails-talk
1

Rails code:

Accessors.send :define_method, :"default_#{name}", &block

Accessors.module_eval <<-METHOD, __FILE__, __LINE__ + 1 def #{name} @details.fetch(:#{name}, ) end

def \#\{name\}=\(value\)
value = value\.present? ? Array\(value\) : default\_\#\{name\}
\_set\_detail\(:\#\{name\}, value\) if value \!= @details\[:\#\{name\}\]
end

remove\_possible\_method :initialize\_details
def initialize\_details\(details\)
\#\{initialize\.join\(&quot;\\n&quot;\)\}
end
METHOD

end

Here we invoke send() on the module Accessors, passing the :define_method symbol, which represents the define_method private method available from Class class. We create an instance method called default_locale, whose value is the block passed from register_detail class method of ActionView::LookupContext. Note that we later use "include Accessors" within LookupContext class to make that available as an instance method of LookupContext. We then create more instance methods using module_eval, with here-documents to specify our delimiter (METHOD) and the dynamic constants (__FILE__, __LINE__) for accurate error reporting on stacktrace. My question is why not include default_#{name} as part of the evaluated string in module_eval, rather than invoking send() directly above that using define_method?

2

John Merlino wrote in post #1075500:

Rails code:

Accessors.send :define_method, :"default_#{name}", &block

Accessors.module_eval <<-METHOD, __FILE__, __LINE__ + 1   def #{name}   @details.fetch(:#{name}, )   end

  def #{name}=(value)   value = value.present? ? Array(value) : default_#{name}   _set_detail(:#{name}, value) if value != @details[:#{name}]   end

  remove_possible_method :initialize_details   def initialize_details(details)   #{initialize.join("\n")}   end   METHOD end

My question is why not include default_#{name} as part of the evaluated string in module_eval, rather than invoking send() directly above that using define_method?

The variation of module_eval() used in the example takes a String as an argument. So "default_#{name}" could certainly be inserted in the String argument because it is a String, but what about the other argument: &block?