From: Eric Mahurin <eric_mahurin@...>
Date: 2005-08-20T04:32:24+09:00
Subject: Re: Non-overridable and non-redefinable methods

--- Eric Hodel <drbrain@segment7.net> wrote:
> On 19 Aug 2005, at 10:03, Eric Mahurin wrote:
> > Another thing that hinders performance optimizations is the
> > lack of the ability to say that a method is not overridable
> in
> > any derived classes.  This mostly applies to many methods
> in
> > Object and Kernel (because everything gets those methods),
> but
> > could apply elswhere if the VM/compiler couldn't determine
> the
> > exact class but possibly the kind_of.  Here are methods in
> > Object that would be advantageous to inline (and not allow
> to
> > be overridden) for performance:
> >
> > __id__   __send__   class   equal?   extend   freeze  
> frozen?
> > id   instance_eval   instance_of?   instance_variable_get
> > instance_variable_set   instance_variables   is_a?  
> kind_of?
> > method   methods   nil?   object_id   private_methods
> > protected_methods   public_methods  
> remove_instance_variable
> > respond_to?   send   singleton_method_added
> > singleton_method_removed   singleton_method_undefined
> > singleton_methods   taint   tainted?   untaint
> 
> I either never call these methods, or would use them for
> making proxy  
> objects.
> 
> send can be quite useful to override, and respond_to? pairs
> with  
> method_missing, so it can't be in the list.  id is used
> extensively  
> by Rails, and is deprecated anyhow.
> 
> I don't see why remove_instance_variable is on the list.  I
> may *not*  
> want to remove certain instance variables.

I'm not saying all of these should be on the list to be
non-overridable/removable.  But, anything you put in this list
could offer a performance advantage in some future ruby
VM/compiler.

The ones I think are most important are:

__id__ (and maybe object_id)
__send__ (and maybe send)
equal?
nil?

Some of these even say in the docs that they shouldn't be
overridden.  And I think when you override __send__, it gives a
warning.  I'm proposing an enforcement to this.  This is
sort-of like "final" in java.  Or not "virtual" in C++.

It seems kind of silly that all of the above has to go through
the method call overhead when the in-lining what these do is so
trivial.

> Also, we couldn't make dead-simple proxies like this:
> 
> class BlankSlate
>    instance_methods.each { |m| undef_method m unless m =~
> /^__/ }
> end
> 
> class Proxy < BlankSlate
> 
>    def initialize(obj)
>      @obj = obj
>    end
> 
>    def method_missing(sym, *args, &block)
>      @obj.__send__(sym, *args, &block)
>    end
> 
> end
> 
> class Foo
>    def x; y; end
>    protected
>    def y; @y = :stuff; end
> end
> 
> foo = Foo.new
> dfoo = Proxy.new foo
> 
> p foo.protected_methods
> p dfoo.protected_methods
> 
> p dfoo.send :x
> p dfoo.instance_variables

You couldn't do this - unless the only
non-overridable/removable methods were __send__ and __id__ -
because the above code didn't want to mess with them.

This is a performance vs. flexibility tradeoff.  You'd want to
find the right list of non-overridable/removable methods to
give the best balance.



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