From: Robert Klemme <bob.news@...>
Date: 2005-10-18T21:56:58+09:00
Subject: Re: A couple of questions/statements from a Ruby neohacker

Christophe Grandsire wrote:
> Selon Robert Klemme <bob.news@gmx.net>:
>
>>
>> I'm not so sure: the history of this list / ng has shown that this
>> issue has irritated people over and over again.
>
> And it has also shown that many people agree with the convention as I
> have stated it. And from the mouth of the master himself (from:
> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/2331):
>
> "Unlike Scheme, not all change-in-place functions are named with
> exclamation mark.  In Ruby, exclamation mark means `MORE dangerous',
> or `may cause surprise' than non-bang counterpart, i.g. in-place
> modification by `gsub!' may let you surprise, comparing copying
> `gsub'."
>
> As long as matz himself keeps with this convention (and he has shown
> no sign of wanting to change it, especially since it would cover Ruby
> with !'s - check the rest of the that thread -), I don't think we
> should either. ! is *not* for destructive methods. It's for methods
> that already exist in a non-bang form, and which do something similar
> to them but in a dangerous way. There are plenty of destructive
> methods that don't have a bang (because they don't have a
> non-destructive version), and I don't believe it would be a gain to
> add a ! to all of them, especially since it would in my opinion break
> the aesthetics of Ruby.

Certainly.  And compatibility would suffer.  Agreed.

>   So the convention that was
>> followed in implementing this might be a different one from the
>> publicly observed one.  One reason for this might be that the term
>> "dangerous" in this context is much broader and less precise than
>> the term "destructive" (changing the receiver's state).  Also
>> "dangerous" is very context sensitive (even IO#puts might be
>> regarded as dangerous in certain situations) which adds to the
>> difficulty.
>
> But in this case it's simple: to get a !, a method has to have a
> counterpart that does about the same work, and be more dangerous
> (destructive, unsafe, etc...) than the other one.

I never looked at it that way.  Thanks for that hint!

>   It might be an interesting
>> philosophical debate which of the two conventions is more adhered
>> to, as a convention is a social thing...
>>
>
> I believe the convention that bang methods always have a non-bang
> alternative, and that destructive methods without a non-destructive
> alternative don't have one, is pretty well followed.

Anomalies I can think of off the top of my head:

 - Hash#update and Hash#merge: those do the same but #merge creates a new
instance while #update doesn't.

 - Even for Array#delete it would make sense to have two variants - one
that returns a copy with selected elements removed and another one that
modifies in place.

> I made a cursory look at about 4 years of the history of the
> Ruby-talk list, and everything I read seems to indicate that the
> convention is pretty well followed. In any case, I don't believe any
> other convention would be better. Just remember that if you think of
> putting a ! on your method you need one without the bang. If it
> doesn't make sense to have such an alternative, your method doesn't
> need a bang.

Makes sense.

Cheers

    robert