Re: -Wconversion versus libstdc++

[Paolo Carlini <pcarlini at suse dot de>]

Hi Gaby,

> There is something that we knoq about the code, that the compiler
> does not have: we expect a sequence denoted by its first and last
> element, so that the difference is always positive.  However, the
> difference of pointers is defined in the language as an ptrdiff_t (a
> signed type).  No wonder what people invented ssize_t :-)
>
> I believe we have to investigate further what promises we want make
> and hold through max_size() and change the code according to that.
>  
First, I want to tell you that I agree with your general point of view, 
here and elsewhere, in particular about the tension existing between 
difference_type and size_type: as a matter of fact, when, time ago, I 
noticed some differences between our vector and deque implementations, I 
wrote something about it in private mail to Howard, but we didn't pursue 
the issue much...

Coming to the specific issue, and *assuming* we agree about the 
usefulness of warning for signed -> unsigned, maybe we are "lucky", in 
this sense: Table 65 says *explicitely* that size_type can represent any 
non-negative value of difference_type. Thus, as I see the issue, we can 
safely cast from the latter to the former, if we want, without entering 
in the larger discussions mentioned above... What do you think?

Paolo.