Inheritence of aliases methods - suprise!

ruby-talk
1

this suprised me today:

     harp:~ > cat a.rb
     class A
       def assertion
         raise NotImplementedError
       end
       alias_method "assertion?", "assertion"
     end

     class B < A
       def assertion
         true
       end
     end

     B::new.assertion?

     harp:~ > ruby a.rb
     a.rb:3:in `assertion?': NotImplementedError (NotImplementedError)
             from a.rb:14

this only way i can seem to make this work is through some self::inherited
hacks or to actually define assertion? in the base class. is there no clean
way to inherit aliases?

regards.

-a

···

--
happiness is not something ready-made. it comes from your own actions.
- h.h. the 14th dali lama

2

this suprised me today:

$ parse_tree_show -
     class A
       def assertion
         raise NotImplementedError
       end
       alias_method "assertion?", "assertion"
     end

     class B < A
       def assertion
         true
       end
     end
[[:class, :B, :A, [:defn, :assertion, [:scope, [:block, [:args], [:true]]]]],
[:class,
   :A,
   :Object,
   [:defn,
    :assertion,
    [:scope,
     [:block,
      [:args],
      [:fcall, :raise, [:array, [:const, :NotImplementedError]]]]]],
   [:defn,
    :"assertion?",
    [:fbody,
     [:scope,
      [:block,
       [:args],
       [:fcall, :raise, [:array, [:const, :NotImplementedError]]]]]]]]]

this only way i can seem to make this work is through some self::inherited
hacks or to actually define assertion? in the base class. is there no clean
way to inherit aliases?

alias copies the method, it doesn't make a pointer to the method.

···

On Feb 6, 2006, at 1:06 PM, ara.t.howard@noaa.gov wrote:

--
Eric Hodel - drbrain@segment7.net - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com

3

This makes sense, If you consider the common idiom of alias'ing a method to wrap additional functionality around it. If alias(_method) didn't work like that you couldn't use it like this. alias_method doesn't work like assignment in ruby, its more like it creates a new method with the same source as the original method.

As a poorly conceived alternative:

% cat a.rb
class Class
   def shallow_alias(new_name, current_name)
     self.module_eval <<-END
     def #{new_name}(*args, &block)
       #{current_name}(*args, &block)
     end
     END
   end
end

class A
   def assertion
     raise NotImplementedError
   end
   shallow_alias "assertion?", "assertion"
end

class B < A
   def assertion
     true
   end
end

B.new.assertion?

% ruby a.rb
%

···

On Feb 6, 2006, at 4:06 PM, ara.t.howard@noaa.gov wrote:

this suprised me today:

    harp:~ > cat a.rb
    class A
      def assertion
        raise NotImplementedError
      end
      alias_method "assertion?", "assertion"
    end

    class B < A
      def assertion
        true
      end
    end

    B::new.assertion?

    harp:~ > ruby a.rb
    a.rb:3:in `assertion?': NotImplementedError (NotImplementedError)
            from a.rb:14

this only way i can seem to make this work is through some self::inherited
hacks or to actually define assertion? in the base class. is there no clean
way to inherit aliases?

regards.

-a

--
happiness is not something ready-made. it comes from your own actions.
- h.h. the 14th dali lama

4

yeah - this is pretty much what i did. for some reason i had always assume
that alias_method worked this way.

regards.

-a

···

On Tue, 7 Feb 2006, Logan Capaldo wrote:

This makes sense, If you consider the common idiom of alias'ing a method to
wrap additional functionality around it. If alias(_method) didn't work like
that you couldn't use it like this. alias_method doesn't work like
assignment in ruby, its more like it creates a new method with the same
source as the original method.

As a poorly conceived alternative:

% cat a.rb
class Class
def shallow_alias(new_name, current_name)
   self.module_eval <<-END
   def #{new_name}(*args, &block)
     #{current_name}(*args, &block)
   end
   END
end
end

class A
def assertion
   raise NotImplementedError
end
shallow_alias "assertion?", "assertion"
end

class B < A
def assertion
   true
end
end

B.new.assertion?

% ruby a.rb
%

--
happiness is not something ready-made. it comes from your own actions.
- h.h. the 14th dali lama