Re: [boost] boost::filesystem request

Subject: Re: [boost] boost::filesystem request
From: Edward Diener (eldiener_at_[hidden])
Date: 2008-10-29 23:33:57

Beman Dawes wrote:
> On Mon, Oct 27, 2008 at 1:18 PM, Andrey Semashev
> <andrey.semashev_at_[hidden]>wrote:
> 
>> Edward Diener wrote:
>>> Jorge Lodos Vigil wrote:
>>>> Hi
>>>> The Traits classes for basic_path provided in the filesystem library
>>>> (path_traits and wpath_traits) are good enough to be used as default
>>>> values for basic_path in most cases.
>>>> However, since they are independent structs, they can not be used to
>>>> instantiate a basic_path with a single String template parameter. I
>>>> would like to write:
>>>>
>>>> typedef basic_string<char> string_t;
>>>> typedef fs::basic_path<string_t, fs::basic_path_traits<string_t> >
>>>> path_t;
>>> I would like to second this request. I also noticed that one can not
>>> easily instantiate a basic_path based completely on a string type,
>>> because of the traits class. If it is at all possible, the traits class
>>> should be a template class based on the string type, with supplied
>>> specializations for std::string and std::wstring.
>> I second that, too. Maybe, a Trac ticket would be a appropriate.
> 
> 
> I'm pretty close to posting a Filesystem Version 3 prototype for feedback.
> Perhaps as soon as this weekend.
> 
> It uses a single class path, with templated member functions. Much simpler
> and more straightforward to use. So the question will become, are these
> member templates flexible enough to achieve what you are trying to
> accomplish? It wouldn't be surprising if some further work were needed, and
> I'll be very interested in getting your comments on the prototype.

The issue for me was just ease of instantiation of a basic_path based 
solely on a string type ( which is actually a character type ). One can 
not currently instantiate a basic_path with:

boost::filesystem::basic_path<std::basic_string<char>,
boost::filesystem::basic_trait<std::basic_string<char> > > myPath;

where one just specifies the character type.

Why would one want to do that ? For two reasons:

1) In a VC++ program which may be multibyte or Unicode depending on a 
compiler option, we would have:

boost::filesystem::basic_path<std::basic_string<_TCHAR>,
boost::filesystem::basic_trait<std::basic_string<_TCHAR> > > myPath;

2) A template class or template function taking a character type 
parameter would just pass that type in to filesystem to instantiate the 
correct type path.

So I do not know whether your version 3 solves makes that easier or not, 
but hopefully it does.