|
Boost : |
Subject: Re: [boost] [1.44] Beta progress?
From: Robert Ramey (ramey_at_[hidden])
Date: 2010-07-26 14:41:09
Matthias Troyer wrote:
> On 25 Jul 2010, at 23:56, Robert Ramey wrote:
>
>> Matthias Troyer wrote:
> Yes, what is missing is the list of special types and their
> interface. In the past they were all STRONG_TYPEDEF, and the
> semantics of STRONG_TYPEDEF was the same as that of the underlying
> integral type. That has changed and broken some code.
>
> The basic issue is that an archive deriving from
> detail::common_[io]archive has to support the fundamental C++ types,
> std:: string, and that collection of special types. In order to
> serialize those special types I need to be able to know something
> about them! The specific list of concepts they model is less
> important than that list being stable (as long as serialization can
> be implemented efficiently). Besides the default constructor it would
> be good to have a type member specifying the (current) implementation
> type:
>
> #define BOOST_ARCHIVE_STRONG_TYPEDEF(T, D) \
> class D : public T { \
> public: \
> typedef T implementation_type; \
> explicit D(const T t) : T(t){} \
> D() : T() {} \
> }; \
A month or so ago I had most of these types implemented with
STRONG_TYPEDEF. In addition to these I had a few
implemented "by hand": tracking_type, class_name_type. So
moving a few from the STRONG_TYPEDEF column to the
"hand rolled" column didn't raise any red flags. I found that
I had to add the following operations to these types:
For T
T:base_type // where base_type is some integer supported by binary_primitive
and text_primitive.
convertable to T::base_type &
convertable to const T::base_type
operator ==
operator<
This was totally ad hoc- I was just "making things work" Of course
STRONG_TYPEDEF supports all of these except base_type which
could easily be added to it at no cost. Soooooo we could
define such a concept and that would solve the current
dilema, avoid future problems, and make mpi_archives
easier to write and more robust. In principle I see this as
an improvement. Of course the devil is in the details.
I see the utility of augmenting STRONG_TYPEDEF but
I wonder about it. if you have code T:base_type and
T is not one of the types we're using - it won't have
this available - compiler error. Wouldn't it be better
to specify the implicit requirements as above and just
know that T will be converted to what one wants? and
sizeof(T) can be applied to both the (now) more elaborate
types as well as C++ primitives.
> and also use the implementation_type member in the other special
> classes. That way you could change those integer types at any time
> without causing any breakage in Boost.MPI. Right now I have to
> manually set these types:
>
> BOOST_MPI_DATATYPE(boost::archive::class_id_optional_type,
> get_mpi_datatype(int_least16_t()), integer);
Though it's off topic at this point, I've never understood what this macro
is for. why do these special types need handling different than any
other common c++ primitive types like integers. Wasn't it enough
for these types to be convertable to integers and references to integers?
> and if you should change class_id_optional_type to be something else
> than int_least16_t the code will break again.
To repeat, I've no problem with the general idea. lets see some
fleshing out of the details.
Robert Ramey
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk