On 2013-05-10 15:01, Roy Smith wrote:
In article <mailman.1527.1368188358.3114.python-l...@python.org>,
Robert Kern <robert.k...@gmail.com> wrote:
I'd be curious to see in-the-wild instances of the anti-pattern that
you are talking about, then. I think everyone agrees that entirely
unmotivated "enable" methods should be avoided, but I have my doubts
that they come up very often.
As I mentioned earlier in this thread, this was a common pattern in the
early days of C++, when exceptions were a new concept and handled poorly
by many compilers (and, for that matter, programmers).
There was a school of thought that constructors should never be able to
fail (because the only way for a constructor to fail is to throw an
exception). The pattern was to always have the constructor succeed, and
then either have a way to check to see if the newly-constructed object
was valid, or have a separate post-construction initialization step
which could fail.
See, for example, the isValid() and Exists() calls for RogueWave's
RWFile class (http://tinyurl.com/c8kv26g). And also,
http://tinyurl.com/cgs6clx.
Even today, there are C++ implementations which do not use exceptions.
Some are for use in embedded or real-time systems where things need to
be strictly time-bound and/or memory-bound. Others are for historical
reasons (http://tinyurl.com/6hn4zo).
Once people were used to writing "can't fail" constructors in C++, they
often continued using that pattern in other languages, where the
underlying reasons no longer made sense. Quite possibly, they never
even knew the underlying reasons; they were taught, "Constructors must
never fail", and assumed it was a universal rule.
Right, this is one of the "bad reasons" I talk about later in my message. The
authors had a reason in their mind for doing it (they thought it was a universal
rule); it was just a bad one. It's more useful to talk about why people thought
they should follow that pattern than to just say "there is no reason to do this".
This, BTW, is one of my biggest beefs with the classic Gang Of Four
pattern book. It presents a bunch of patterns as being universally
applicable, when in reality many (if not most) of them are highly C++
specific.
BTW, whenever I read things like, "I think everyone agrees", I
automatically assume what the writer really meant was, "I, and all the
people who agree with me, think".
Hah! Fair enough. I actually meant it to emphasize that I thought that Steven
was overly reducing his statements to something that was trivially true,
sacrificing content for validity. I will suggest that your interpretation of
that phrase is more appropriate when the speaker is proposing something of their
own rather than (partially) conceding a point. The exaggeration is only
self-aggrandizing in the former case.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
--
http://mail.python.org/mailman/listinfo/python-list
