Re: [cpp-netlib-devel] Dependence on std::string

[Cheng L. <rhy...@gm...>]

By the way, I wish that Dean may explain the seven proposed tags in 
detail, especially the binary tag and the stream tag which seems may 
feed my appetite :-D

连城 wrote:
> Hi, Glyn
>
> I am recently working on a binary protocol oriented network framework
> based on ASIO in my project. So I do care more about a binary protocol
> oriented message type. so I have once asked Dean a question during a
> private communication:
>
>    What's the granularity of the Tag template parameter of
>    basic_message<> template? One tag per message type (I means
>    text/binary here) or one tag per protocol?
>
> And Dean replied:
>
>    The Tag template parameter is meant to differentiate the message
>    types -- for easy extension. That means, to be clear, the message
>    tags I envision are:
>
>    tags::unicode
>    tags::text (tags::default_)
>    tags::binary
>    tags::stream
>    tags::serializable_text
>    tags::serializable_binary
>    tags::serializable_xml
>
>    Among many others I haven't thought of yet. :D
>
>    They are tags, because I don't intend to put the overhead of an
>    abstract message class as the base class for all the message
>    types.  That allows us to implement a basic_message<tags::text>
>    and basic_message<tags::binary>, and specialize the
>    implementations without having to rely on inheritance and runtime
>    polymorphism.
>
> As Dean stated, with such tags, we can specialize different message
> types. And I think the message type tags should imply the underlying
> storage policy of that type of basic_message. Say, tags::text
> (tags::default_) implies an std::string storage facility, while
> tags::unicode implies an std::wstring storage facility, and
> tags::stream may implies a boost::asio::streambuf storage facility (as
> what I've done in my own project). So I suggest we could include a
> storage_type in the tags struct:
>
>    struct tags {
>        struct default_ {
>            typedef std::string storage_type;
>        };
>
>        typedef default_::text;
>
>        struct unicode {
>            typedef std::wstring storage_type;
>        };
>
>        struct stream {
>            typedef boost::asio::streambuf storage_type;
>        };
>
>        ...
>    };
>
>    typedef basic_message<tags::text> message;
>    typedef basic_message<tags::unicode> wmessage;
>    typedef basic_message<tags::stream> smessage;
>    ...
>
> Would this be sane?
>
> Cheers
> Cheng
>
>
> Glyn Matthews wrote:
>> Guys,
>>
>> I've been giving a little thought to something Dean mentioned in his 
>> last message about using std::string in the network library.
>>
>> The first thing I thought of was that Dean stated that "everything is 
>> a template".  Apart of course from std::string.  I have created a 
>> branch in SVN named gxm) which replaces all references to std::string 
>> with an extra template parameter.  Happily, this passes all the 
>> original tests (with an additional template specialization so that 
>> const char * is converted to a std::string).  However, this creates a 
>> problem (certainly with GCC) because the wchar_t typedef is the same 
>> as char and its not possible to overload const wchar_t * in the same 
>> way.  So the following code will not compile:
>>
>> wmessage wmsg;
>> wmsg << header(L"wide characters");
>>
>> Another thing I see is that boost filesystem and boost 
>> program_options have dealt with a very similar problem to this.  But 
>> if we use the same approach (see the file 
>> "boost/detail/utf8_codecvt_facet.hpp" )  then we'd have to accept the 
>> use of a cpp source file, meaning we will no longer have a header 
>> only library.
>>
>> What do others think about this?
>>
>> G
>>
>> ------------------------------------------------------------------------
>>
>> ------------------------------------------------------------------------- 
>>
>> This SF.net email is sponsored by DB2 Express
>> Download DB2 Express C - the FREE version of DB2 express and take
>> control of your XML. No limits. Just data. Click to get it now.
>> http://sourceforge.net/powerbar/db2/
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> Cpp-netlib-devel mailing list
>> Cpp...@li...
>> https://lists.sourceforge.net/lists/listinfo/cpp-netlib-devel
>>   
>
>