Re: [cpp-netlib-devel] Uring over here

[K. G. <kim...@gm...>]

Hi Dean,

I'm not John, but his code got me thinking...

On Sun, Oct 26, 2008 at 15:14, Dean Michael Berris
<mik...@gm...> wrote:
>
> On Fri, Oct 24, 2008 at 5:38 AM, John P. Feltz <jf...@ov...> wrote:
>>
>> I implemented this in a similar network client project some time ago:
>>
>> namespace rfc3986 {
>>  template <
>>      typename ParserInput = std::string,
>>      typename Scheme = std::string,
>>      typename Authority = std::string,
>>      typename Path = std::string,
>>      typename Query = std::string,
>>      typename Fragment =std::string
>>    > class URI {
>>      public:
>
> We use traits for these things, and have a simple 'Tag' template argument.

What's interesting about John's approach is not that std::string is
configurable, but that he can write a specific parser for each part of
the URI, and maybe compose them in the full parse() function.

>>      private:
>>        typedef URI< ParserInput, Scheme, Authority, Path, Query,
>> Fragment> Output;
>>
>>        friend Output* parse< ParserInput, Output>
>>          (std::stack<std::string>& errors, const ParserInput& input);
>
> Why a friend class for the parsing?

Friend function. Presumably because you can easily add new parsers. I
think the main parser works something like this:

template< class Input, class Output >
Output* parse(const Input& input)
{
  return NULL;
}


template< >
URI<>* parse(const URI<>::ParserInput& input)
{
   URI<>::Scheme_type scheme = parse<URI<>::ParserInput,
URI<>::Scheme_type>(input);
   URI<>::Authority_type host = parse<URI<>::ParserInput,
URI<>::Authority_type>(input);
   // ...

  return new URI<>(scheme, host, ...);
}

What I think is interesting about this is that we can let the
authority be represented by a string where we don't care much about
the details (e.g. mailto scheme) or a typed struct where we do (e.g.
http scheme), and just provide a new type + corresponding parser to
make it work.

Not sure if I'm reading too many capabilities into John's design, but
I figure this is its main benefit.

- Kim