Re: lvalue required as increment operand -- why does the Standard
requires this for fundamental types only?
On 3 Jul., 11:52, Paavo Helde <myfirstn...@osa.pri.ee> wrote:
Pavel wrote:
SG wrote:
On 2 Jul., 19:30, Pavel wrote:
What is the rationale for this lvalue requirement if there is one?
There is abolutely no reason [for C++] to support prefix ++ on things
that don't refer to any object.
Thanks, I knew that already. This was not not my question. The
question was about the specific rationale for this decision of the
Standard's authors.
You are missing the point.
I have the same feeling. Maybe I left out some detail that is obvious
to most but not Pavel.
Supporting ++ on non-objects is logically
infeasible, [...]
....because ++ means "increment that thing and return the new value"
and you don't want 5 to be 6. ;-) But maybe I simply didn't get the
question.
As for genericity: You may implement your own iterator's prefix ++ via
a member function. But incrementing rvalue iterators is still not part
of the iterator concept! Otherwise, raw pointers wouldn't be
iterators. If you want to code generically you better limit yourself
to the concepts' interfaces.
The standard library of the upcoming C++ ISO standard will provide two
helper functions: prev and next after including <iterator>. Then you
can write things like
auto second = next(container.begin());
if you want to. I think Boost provides something similar already and
it's easy to do it yourself:
template<class Iter>
inline Iter next(Iter it) { std::advance(it,1); return it; }
Cheers!
SG