[boost] Re: path::leaf()

From: David Abrahams (dave_at_[hidden])
Date: 2003-08-25 21:03:15

Beman Dawes <bdawes_at_[hidden]> writes:

> At 03:55 PM 8/21/2003, David Abrahams wrote:
>
>  >Beman Dawes <bdawes_at_[hidden]> writes:
>  >
>  >> At 08:31 PM 8/19/2003, David Abrahams wrote:
>  >>  >
>  >>  >It surprised me a bit that leaf returns a string instead of a path.
>  >>
>  >> The rule isn't entirely obvious. If a decomposition function can
>  >> possibly return more that one element, it is returned as type path. If
>  >> at most a single element is returned, the return type is std::string.
>  >
>  >It may not surprise you, but the easy translation between paths and
>  >strings really rubs me the wrong way.  Practically the only reason I'm
>  >using the path class at all is to increase the level of abstraction
>  >and self-documentation of the code I'm writing -- I think it's foolish
>  >to pass around something called std::string when it really represents
>  >a file path.  A single component of a path is still a path, and it
>  >shouldn't devolve into a string.
>  >
>  >I'm rewriting some Java code in C++ which has a "Directory"
>  >abstraction, that lets you open files in that directory.  I want those
>  >functions take path parameters.  I want to assert that they're leaf
>  >paths.  Having to write:
>  >
>  >    assert(path(p.leaf()) == p)
>  >
>  >or
>  >
>  >   assert(p.leaf() == p.string())
>  >
>  >instead of:
>  >
>  >   assert(p == p.leaf())
>  >
>  >really feels odd to me.
>
> What about:
>
>      assert( p.branch_path().empty() );
>
> Isn't that closer to what you are trying to express?

I guess so.  I didn't see branch_path().  

>  >>  >Shouldn't
>  >>  >
>  >>  >   "foo/bar"/p.leaf()
>  >>  >
>  >>  >work?
>  >>
>  >> Yes, via the automatic conversion. I just added a test case to
>  >> path_test to verify that. Yes, it does work. I expect there would
>  >> have been scads of bug reports if it didn't work.
>  >
>  >Whoa.  What code and compiler did you test that with?
>
> Ah! I corrected your code first so that "foo/bar" was a path. There is
> no operator/ for string arguments, of course.

Of course; that was the point of what I was saying.  you can write
cstring/path, but not cstring/std::string; I think it's reasonable to
combine the leaf of a path with path strings if that's something you
can normally do with a full path.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com