Re: [Boost-users] [mpl] possible bug in insert<set, x>

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2005-10-10 02:23:35

Geoffrey Romer <geoff.romer_at_[hidden]> writes:

> On 10/7/05, Geoffrey Romer <geoff.romer_at_[hidden]> wrote:
>> I'm having trouble with insert<> as called on a set. Specifically, it
>> doesn't seem to be possible to iterate over sets built with insert<>.
>> The following code, for example, works correctly (or at least,
>> compiles without errors):
>>
>> ---
>> typedef set<double, char> m_set;
>> typedef transform<m_set, lambda<identity<_1> > >::type result;
                            ^^^^^^^^^^^^^^^^^^^^^
                            identity<_1>

>> ---
>>
>> but the following (which as I understand it should be equivalent)
>> fails to compile:
>>
>> ---
>> typedef insert<insert<set<>, double>::type, char>::type m_set;
>> typedef transform<m_set, lambda<identity<_1> > >::type result;
                            ^^^^^^^^^^^^^^^^^^^^^
                            identity<_1>

>> ---
>
> On the assumption that this is a bug, 

It is, thanks for the report.

> or at least a non-obvious usage
> error, can anyone suggest a workaround? 

Try this:

   typedef insert<insert<set0<>, double>::type, char>::type m_set;
                         ^^^^^^
   typedef transform<m_set,identity<_1> >::type result;

> At present I can find no way
> to insert an item into a set in a way that produces a usable set, and
> this is a major obstacle in the project I'm working on.
>
> Also, is boost or boost-users the preferred forum for these sorts of
> questions? boost-users seems more appropriate (since this may, after
> all, be an error on my part), but I've found boost to be much more
> responsive.

As far as MPL is concerned, there is no intentional discrimination of
them on my side, but I think the developers list definitely has more
readers that would be able to comment on the library problems of
similar nature, and your posts would be well appropriate there.

-- 
Aleksey Gurtovoy
MetaCommunications Engineering