From: dblack@...
Date: 2003-02-12T11:28:01+09:00
Subject: Re: Operator reordering, good idea? (was Re: ruby-dev summary 19457-19539)

Hi --

On Tue, 11 Feb 2003, Tanaka Akira wrote:

> Do you have any example for == which should not be commutative?

Well, I would have thought this:

  Exception.new("a") == "a"

:-)  But seriously...  my problem with that example being "true" is
that it's only using Exception#to_s after doing a kind of
right-to-left backtracking, *after* seeing that a String object is --
no, *was* -- needed.  My instinct is to say: if you get as far as
having sent a message to an object, it's too late to reconsider what
that object is.

Also, if == can backtrack, why not:

  Exception.new("a") << "b"  #   #<Exception: ab>

and so on.

"Why not?" might be: having everything be exactly consistent and
symmetrical isn't necessarily best for the language, and what's good
for == isn't automatically good for << and others.  But I think having
any of this kind of right-to-left backtracking and re-evaluation feels
very anomalous.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav