Re: [Boost-users] Assignment of ptr_container<A>::iterator value to ptr_container<B>::iterator variable

Subject: Re: [Boost-users] Assignment of ptr_container<A>::iterator value to ptr_container<B>::iterator variable
From: Rob Desbois (rob.desbois_at_[hidden])
Date: 2011-09-29 10:14:05

Thanks Thorsten.
Apologies - I realised I got the email subject wrong, duh.

I've filed this as ticket #5961 (https://svn.boost.org/trac/boost/ticket/5961).

I presume the reason you implemented it like this is to support
comparing C::iterator with C::const_iterator types.
The standard library iterators support this without allowing
comparison between differently-typed iterators by making the container
type a template parameter for the iterator, and hence the comparators
too. Single container type, 2 iterator types allows the necessary
stuff without being too relaxed.

I've submitted a proposed patch (#5963 @
https://svn.boost.org/trac/boost/ticket/5963) which ties the
originating container type to the iterator type, and the passing of
this through the template structures from the most-derived container
types through the base layers and the traits classes (set_config /
sequence_config).
All tests in libs/ptr_container/test pass, and I've confirmed
separately that the original behaviour of allowing
operatorXX(const_iterator, iterator) is still supported (which is what
the tests do), whilst comparing iterators from different container
types is no longer allowed.
I didn't make any changes to the map container and iterator since it
seems they already behaved as expected.

Hope it's all fine. All the best,
Rob

On Wed, Sep 28, 2011 at 5:25 PM, Thorsten Ottosen
<thorsten.ottosen_at_[hidden]> wrote:
> Hi Rob,
>
> Den 28-09-2011 17:39, Rob Desbois skrev:
>>
>> So I've got a few ptr_container instances floating around, and have
>> just tracked down a bug caused by (my) naff code essentially akin to
>> the following:
>>    ptr_vector<int>  vi;
>>    ptr_vector<string>  vs;
>>    bool eq = (vi.begin() == vs.begin());
>>
>> After digging I discovered the operator in question in
>> void_ptr_iterator.hpp:
>>   template<  class VoidIterT, class T, class VoidIterU, class U>
>>   inline bool operator==( const void_ptr_iterator<VoidIterT,T>&  l,
>>                           const void_ptr_iterator<VoidIterU,U>&  r )
>>
> [snip]
>>
>> Is there any sensible way to suppress this behaviour, or are there any
>> comments on why I might be being a muppet?
>
> We can't fix it until we update the code. I agree it is unfortunate behavior
> that we should try to avoid.
>
> I have forgot why I implemented it that way, but I suspect it might have
> been to work around
> various compiler issues.
>
> Anyway, please file a bug report, and then I'll see if I can fix it.
> Or, even better, provide a patch.
>
> kind regards
>
> -Thorsten
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--
Rob Desbois
Eml: rob.desbois_at_[hidden]
Tel: [phone]
"I disapprove of what you say, but I’ll defend to the death your right
to say it", Voltaire