From: John Carter <john.carter@...>
Date: 2008-03-12T06:40:33+09:00
Subject: Re: Best practices for Ruby Meta-programming

On Tue, 11 Mar 2008, Robert Dober wrote:

> def attr_reader *atts
>   atts.each do |att|
>      define_method att do instance_variable_get "@#{att}" end
>   end
> end
>
> is definitely for the programmer, it also should rather run at runtime
> than at compile time.

This topic is about Best Practices for Meta-Programming.

And you have just handed me a brilliant example of why human readable
intermediate representation _is_ Best Practice...


Hmm. Is
   attr_read :foo
really equivalent to a plain getter?

   define foo
     @foo
   end

The way I read your code it's equivalent to...

   define foo
     instance_variable_get "@foo"
   end

Which is probably slower.

Either way the very fact we need to think about it illustrates the
value of human readable intermediate representations!

How about...

   def make_getter( att)
     "define #{att}
   @#{att}
   end
   "
   end

   def Module.attr_read( *atts)
     atts.each do |att|
       self.class_eval( make_getter( att))
     end
   end

Note I have a bug in make_getter...

The class_eval failed for some mysterious reason, so I said...
   puts make_getter("foo")
And got...
   define foo
    @foo
   end

Oops! I see the problem...it should be...
   def make_getter( att)
     "def #{att}
   @#{att}
   end
   "
   end

And I get...
   puts make_getter("foo")
And got...
   def foo
    @foo
   end


Yip that worked.

John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
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