Re: [Boost-users] Forward declarations and iterator_facade<>

Subject: Re: [Boost-users] Forward declarations and iterator_facade<>
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2010-10-15 18:49:40

On Fri, Oct 15, 2010 at 11:02 AM, David Abrahams <dave_at_[hidden]> wrote:
> At Fri, 15 Oct 2010 17:24:42 +0100,
> Phil Endecott wrote:
>>
>> Dear Experts,
>>
>> I have code something like this:
>>
>> struct S;
>>
>> class iter:
>> Â  Â public boost::iterator_facade<iter,S,......>
>> { ... };
>>
>> struct S {
>> Â  Â ...
>> };
>>
>>
>> This used to work, but stopped recently; I believe it may have been
>> after upgrading gcc, not after upgrading Boost itself, but I'm
>> uncertain about that. Â The problem is that something inside
>> iterator_facade calls boost::is_POD<S>, which (not unreasonably)
>> doesn't seem to work for the forward-declared S.
>>
>> I've never been entirely sure what you're allowed to do with
>> forward-declared types like that. Â Was I just lucky that it worked
>> before, or is this a regression?
>
> I guess you were just lucky, because we never tested for or intended
> to provide that capability.
>
>> Re-ordering the code to remove the circular dependencies will be
>> painful, so if anyone has any other hints I would love to hear them.
>
> I'm afraid there's not going to be any other choice for you unless we
> are somehow able to add that capability in Boost and you are able to
> wait for it.

Shouldn't he be able to just specialize boost::is_pod on his forward
declared type as true?