Message du 03/05/11 04:37 De : "Vladimir Batov" A : boost@lists.boost.org Copie à : Objet : Re: [boost] [review] string convert
Gordon Woodhull woodhull.com> writes:
I also want to mention type-to-type conversion, which Vicente Botet has thought out much more thoroughly in his Conversion library. This library offers type-to-type conversion seemingly as an afterthought, just because the syntax allows it.
I have to disagree. Again I consider 'convert' to be more of a conversion framework rather than a library. Indeed, 'convert' does not provide much more beyond string-to-type conversions because I personally did/do not need more. However, it does not mean I/we should deny that possibility to others as their needs may differ. Therefore, 'convert' was designed with that in mind. If Vicente needs type-to-type conversion functionality, I think he might consider implementing that functionality within the 'convert' framework by extending the 'convert' library for everyone's benefit.
Vladimir, as you know I started Boos.Conversion as a more generic response to type-to-type conversion. Your design was limited to string conversion and your library was named StringConvert. Then you redesigned your library so now you are able to make type-to-type conversions also, but the interface is not satisfactory for me, for my taste.
I'd really like to know why you think it's necessary to do convert::from(s) rather than the much more familiar and easy-to-grasp string_convert(s).
I am not sure if I managed to explain that above. The reason why TypeIn and TypeOut need to be separated is that if we have specialization for, say, string-to-type enabled with
template typename boost::enable_if, TypeOut>::type convert_to(StringIn const&) {...}
then, say, string-to-bool further specialization/optimization won't be possible
template bool convert_to(StringIn const&) {...}
It won't compile as both "specializations" will match. It did not work for me. If you can get it to work by some other means, I'll be only happy.
I think the way Boost.Conversion is designed allows such overloading. It use a dummy parameter taking the type of the return type. template typename boost::enable_if, TypeOut>::type convert_to(const StringIn& from, boost::dummy::type_tag const&); template bool convert_to(const StringIn& from, boost::dummy::type_tag const&); The library provides a convert_to function that adds the specific dummy parameter. I recognize this is tricky and that the overloading seems not natural from the user perspective but it works at least for the cases I have tested. Best, Vicente