From: dblack@...
Date: 2007-08-16T11:19:31+09:00
Subject: Re: ! semantics

Hi --

On Thu, 16 Aug 2007, Simon Krahnke wrote:

> * <dblack@rubypal.com> (13:48) schrieb:
>
>>> That's because of the completeness of the library. Whenever there can be
>>> a non-modifying partner, there is one.
>>
>> ! does not mean modifying; it means "dangerous".
>
> Most methods flagged with a ! are dangerous because they modify their
> receiver.

Many of them are, but there's no cause-and-effect between modifying
and !. If there were, there would be !'s on all modifying methods. I
think we should really put that to rest; the convention just doesn't
work that way, and never has.

>>> When you just define a modifying method, is not right to name it without
>>> a ! just because you choose not to define a non-modifying version.
>>
>> I would never add a ! to a method name solely because it changes the
>> receiver. That's a re-invention of what ! is for.
>
> No, you add it because someone might else assume it is a non-modifying
> method, that is what makes it dangerous.
>
> Array#pop is modifying but not dangerous, because everyone expects it to
> be modifying.

If the name doesn't connote destructiveness, then you should change
the name. For example, I would not use the name "last" instead of
"pop", because "last" does not connote destructiveness.

But I also wouldn't use "last!". Just adding a ! does not change a bad
name for a destructive method into a good name. It just adds a !.

>>> What if some other developer wants to add the non-modifying version?
>>> He would have to rename your version.
>>
>> I think that's a solution in search of a problem.
>
> No, that's a problem.

Not really. If I have a "pop" method, and someone wants to write
"last" (i.e., return the last element but not destructively), they
don't have to write "pop!-minus-!". They should choose the best name,
which may have nothing to do with the name I gave the destructive
method.

In other words, m/m! is not the only possible ratio between methods.
There's also m/n, which can be just as close as m/m!. pop/last is an
example; so is concat/+ (also for arrays).

>> Just name your methods clearly, without !. Then, if you (or someone
>> else) want to add a "dangerous" version, you can write the ! method.
>
> You are the one who's proposing that something isn't dangerous because
> there currently isn't a less dangerous version.

I don't think I can quite follow all the convolutions we're getting
into :-)  I've posted something about the ! on my blog, if anyone's
interested:

http://dablog.rubypal.com/2007/8/15/bang-methods-or-danger-will-rubyist


David

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