Dear all,
in a number of projects now, I’ve been (ab)using the convention of using
exclamation marks at the end of method names somewhat and was therefore
wondering about the current consensus in the community regarding the use
of exclamation marks.
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)
d.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). 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:
name.sort_order!.to_s #-> set name to sort order formatting and convert
to string
What do you think? Is it a terrible idea to break conventions like that
and would you discourage or condone such usage? 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?
Thanks!