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\(&quot;\\n&quot;\)\}
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?

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?