Subject: Re: [boost] Heads up - string_ref landing
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-12-16 15:09:37
on Sun Dec 16 2012, Yakov Galka <ybungalobill-AT-gmail.com> wrote:
> On Sun, Dec 16, 2012 at 12:48 AM, Dave Abrahams <dave_at_[hidden]> wrote:
>> on Wed Dec 12 2012, Gottlob Frege <gottlobfrege-AT-gmail.com> wrote:
>> > Qt's QString has both empty() and isNull() and they are not always the
>> > same. Basically empty() is a zero-byte string, but null is a
>> > never-been-set-or-allocated string.
>> That's dumb, though.
> It is the matter of value semantics vs. pointer semantics. QString is "more
> like" a pointer to a referenced counted string.
But that's a dumb thing for QString to be ;-)
>> > ie
>> > QString name = database.get("Name");
>> > name.empty() == true means the Name field was empty name.isNull()
>> > == true means the Name field doesn't exist in the database.
>> > Somewhat like optional<string>.
>> > I am NOT saying whether this is a good thing. Just a widely known
>> > example of interpretation.
>> I AM saying it's a bad thing! :-)
> I agree with you that the null state of QString is a bad thing. But this by
> itself does not justify interpreting an empty() string to be false. Let me
> The conversion to bool usually tests the validity of the object
Now hold on a minute! I don't buy this premise. In what sense is a
null pointer or a zero integer "invalid?"
> so one can do some other operations on it. For instance this is what
> it means in iostreams (stream is in non-fail state so one can continue
> reading & writing to it)
> and pointers (not null so one can dereference it).
It tests for a useful singular state.
But if you want to follow this line of reasoning...
front(), back(), and operator (probably among others)
can't be used on an empty string.
> These examples are of well understood validness of states. On the
> other hand, for strings, it is dubious that empty() strings are in any
> way invalid.
Just as it's dubious that a null pointer or a zero integer is in any way
> All operations still can be done on them, like concatenation, find,
> operator  with index <= size(), etc...
> Having said that, personally I do not object to empty() being
> interpreted as false. I am only trying to judge this suggestion
-- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost
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