-----Messaggio originale-----
Da: Robert Klemme [mailto:shortcutter / googlemail.com] 
Inviato: luned14 novembre 2011 16:49
A: ruby-talk ML
Oggetto: Re: Exclamation marks in method names

On Mon, Nov 14, 2011 at 1:08 PM, Sylvester Keil <sylvester.keil / gmail.com>
wrote:
> As outlined in the Matz/Flanagan book (also in Pickaxe and, I believe, I
read about it the Best Practices book, too), the prevailing convention is to
use exclamation marks for methods that should 'be used with caution'; common
examples include mutators (when there is also a nonmutating variant), or
methods that raise errors (when there are variants that fail 'silently' by
returning a known good value or a default value). I have used exclamation
marks in both these contexts, however, I've also come up with a different
idiom recently, mainly in combination with predicates.
>
> As we know, predicates (or predicate-like state) can often be accessed
using methods ending with a question mark like #empty?, #nil? etc. Now, in
cases where the predicate's state is determined solely by an attribute, I
started using methods with exclamation marks to set the value. For example,
consider a Date class that is supposed to handle uncertain dates:
>
> d = Date.new
> d.uncertain? #-> false
> d.uncertain! #-> make date uncertain (instead of d.uncertain = true) .uncertain? #-> true d.certain! #-> make date certain again
>
> These methods are mutators, but they are not really dangerous (and there
are no non mutating variants), so this usage is in violation with the naming
convention. Nevertheless, I've grown quite fond of the symmetry (using both
? and ! for predicates), going so far as adding separate accessor generators
(think attar_predicate).

That would be totally unobvious to me.  I would rather expect (and be
looking for) a "=" sign somewhere to update the property / attribute.
That also has the advantage to treat all attributes alike when it comes to
updating.  Not sure whether this in itself is such a big win but the
readability loss could be significant.

> To make matters worse, I broke another convention: in Ruby, the
exclamation mark mutators usually return self only if a mutation actually
took place (nil otherwise), for example:
>
> 'U'.upcase! #-> nil
>
> and are therefore not chainable. Because I wanted the predicate-setters to
be chainable, I made them return self always. For instance, I had a Name
class that printed names according to different formatting rules and I
wanted to write things like:

Chainability is useful sometimes but I am in doubt whether it is such a big
asset.  I'd probably judge convention higher.

> name.sort_order!.to_s #-> set name to sort order formatting and 
> convert to string

Doesn't look good to my eyes.

> What do you think? Is it a terrible idea to break conventions like that
and would you discourage or condone such usage?

Well, conventions are there to make our lives easier.  If you break a
convention you need to compare the cost with the benefit.  If you intend to
make the code from these projects public I'd say costs (= negative impact)
clearly outweigh benefits, because your convention is not compatible with
the "core convention".  Even for purely internal project I am not sure
whether it is such a good idea.  New people need to get used to it (which is
probably not too bad), but if you look at other code you will constantly
have to adjust your expectations (i.e.
foo! is chainable in your case while it is not generally in other
code) etc.  I think the "beauty" to nicely align methods with punctuation
(!?) is not as important as the obstacles to reading and writing code in an
environment with your replacement convention.  And:
if it ain't broken, don't fix it - could be read as "don't change
established conventions unless you have very good reasons".

> Also, I'd be curious to know if there were any other common conventions
regarding the use of exclamation (and question) marks in method names?

I am not aware of any other right now.

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/


 
 
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