From: Logan Capaldo <logancapaldo@...>
Date: 2006-03-13T14:52:26+09:00
Subject: Re: [RCR] abstract method in Ruby

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On Mar 12, 2006, at 10:08 PM, kwatch wrote:

>
> What you say is right.  I agree with your opinion.
> My point is that program code should be descriptive and
> it should be prime documentation than comment or api doc.
> Abstract method helps this.
>

I don't believe it is any more descriptive than the current  
situation. I think that whenever possible, you are right code should  
be self-describing, but I don't think abstract methods are self- 
describing.

I think that in ruby this already _is_ self describing:

module Enumerable
   ...
   def map(&block)
         results = []
         each { |x| results << block.call(x) }
          results
   end
end

Looking at this a programmer using this api will say, ok I need to  
provide an each method,
and it needs to take a block. That's what the code tells him. If he  
doesn't read the code, and attempts to use Enumerable, he will get an  
exception. This exception will tell him what method his object  
doesn't implement that enumerable relies upon. This exception may be  
a NoMethodError, or a NotImplementedError. Either way though he has  
to go back to the code or docs to see what is expected. Implementing  
an each that doesn't take a block or an each that takes more or less  
arguments than its expected too is just as bad as or worse than no  
each at all. I digress though, because what it really comes down to   
is that your abstract_method should be a comment or an rdoc  
directive. It really, really should. There is no reason to write code  
that does effectively nothing. Your abstract method (irrespective of  
abstract methods in other languages) is a documentation tool, and  
that's where it should be implemented. You say "consider  
readability", so do I. What is more readable, a comment telling me I  
need to have an each method to include Enumerable, possibly even  
explaining why, or a a call to a class method named abstract _method?  
Now admittedly I can guess what that means, but I still have to find  
out to be sure. Especially since it looks like its doing something. A  
comment can be just as short as your method call, doesn't introduce  
any new code and it IS part of the code, unless you read your code  
with all the comments stripped out. You keep saying code should be  
descriptive, I don't believe this adds to the descriptiveness. Which  
is why I would not want this in the core ruby. It doesn't add anything.
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