Rozental, Gennadiy wrote:
4. How does this all machinery will work with wchar_t?
std::wcout << formatob( vec, containerfmtex< wchar_t *
()).format( L" - " );
Use the ex< DelimiterType > variant on the innermost construct.
This is inacceptable and does not follow standard practice.
The new version templates that are templatized on character type are also templatized on the format object that they use (to render their elements). This means that in order to provide c/w-style interface, you need: template< typename CharT, class ElementRenderer = basic_default< CharT >
class basic_container{ ... }; basic_container< char > ccontainer(){ return( basic_container< char >()); } basic_container< char, ElementRenderer > ccontainer( const ElementRenderer & er ){ return( basic_container< char >( er )); } basic_container< wchar_t > wcontainer(){ return( basic_container< wchar_t
()); } basic_container< wchar_t, ElementRenderer > wcontainer( const ElementRenderer & er ){ return( basic_container< wchar_t >( er )); }
// what about custom character type (e.g. unicode?) basic_container< char > my_format = ccontainer().decorate( " : " ); std::cout << io::object( vec, my_format ); std::cout << io::object( vec, ccontainer().decorate( "< ", " >" ));
This is a VC 6.x workaround.
But you don't list this compiler amoung supported.
At the moment there are a few problems with it. I am looking to resolve these if possible.
6. Why the same entity you sometime call format_type and sometime DelimeterType?
format_type is the typedefed version (should be delimiter_type) and DelimiterType is the template parameter.
So is it delimeter type or forat type - it can't be both.
delimiter type. In the new version it is char_type since the decorators (formatters in the review implementation) now take a CharT parameter instead of the storage type.
7. What deducer is supposed to deduce? I couldn't get through all the details, but couldn't the same be achieved using partial specialization and/or partial ordering. Cause it look way too complex and unnecessary.
The deduction mechanism is used to evaluate what type T is (e.g. std::pair< char, int >), what format object is needed to render it (including nested format objects) and to construct the appropriate format object.
It could be possible to use partial specialization, but the type traits are used elsewhere to redirect formatting behaviour (e.g. when reading in a container do diffreent things if it is a sequential, associative or set container).
IMO all that you needed is function overloading. I don't see a place for all these deduce/trats staff.
Consider the pair format object (pair renderer): how do you render each pair type. Using function overloading, you would have: class basic_pair { public: OutStream & write( OutStream & os, const std::pair< T1, T2 > & p ){ ... } OutStream & write( OutStream & os, const boost::compact_pair< T1, T2 > & p ){ ... } OutStream & write( OutStream & os, const std::complex< T > & p ){ ... } OutStream & write( OutStream & os, const boost::math::interval< T > & p ){ ... } }; But this would add dependencies on those libraries. Also, it is not extensible: how do you add support for boost::rational< T >, for instance? Using the deduction mechanism, I implement the output using boost::io::detail::getval< n >( pair_type ). Input is more complex because you need to distinguish between types that you can get the elements separately (e.g. std::pair) and types that you need to set both values together (e.g. boost::math::rational): the former uses refval< n >( type ) and the latter uses assignval( type, first, second ). How would function overloading solve this? (Note, function overloading is used for getval, refval and assignval). For containers, you need to use a different function/function arguments to insert an element depending on whether the container is sequential, associative or a set. My library provides a description of the types that it can render (e.g. separable pairs, 4-ary types, associative containers) without saying what these types are. The stl and boost directories in my library then tell my library that a std::vector is a sequential container. My library then knows how to handle a std::vector. Doing this, I can separate the dependencies on external libraries and allow it to be extended to support other sequential containers, pairs, etc.
11. Need for all this hierarchies: Formatter->formater_t->openclose_formatter_t
This is to ensure that the return type of 'format' in Formatter [FormatObject] is Formatter and not openclose_formatter_t. Thus: formatob( vec, containerfmt().format( " / " )); will work as intended without overriding 'format' in containerfmt_t (created by containerfmt()) to return the correct type.
openclose_formatter->openclose_formatter_t
are completely unclear. Explanations presented in docs does not help since format methods seems to be returning *this anyway.
They return: *static_cast< ReturnType * >( this ) to allow 'format' to return the correct type when inherited in the format objects.
Formatob_t::format return *this. You did not answer my question. I still believe it's all unnecessary.
formatob_t::format returns *this because the FormatObject (Renderer) that it inherits returns a value of type FormatObject. Thus, if you didn't have these overloads, then: std::cout << formatob( vec ).format( " + " ); would not work, since it will try to output a containerfmt() type.
Why couldn't we just use something trivial like
template<char Ch> struct formatter { std::basic_string<Ch> m_open; std::basic_string<Ch> m_close; std::basic_string<Ch> m_sep; };
Is beyond me. If any member is empty it means it missing.
This is the direction I am going in the development version. The only difference is that I am using io::decoration< CharT, int id > instead of std::basic_string< CharT >. The decoration class uses std::basic_string to store the values, while providing support for looking up the default value on a stream and an external function for checking for a match on an input stream.
You presented library call *Output* formatter. Why do we talk about input at all.
The *output* designation is a "legacy" from before the library supported input facilities. People expressed an interest in inputting as well, so I added it; output stuck. Regards, Reece _________________________________________________________________ Use MSN Messenger to send music and pics to your friends http://www.msn.co.uk/messenger