Forum: Ruby on Rails define_method vs module_eval

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

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?

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 &block?