Re: [boost] [Filesystem] v3 path separator changes

Subject: Re: [boost] [Filesystem] v3 path separator changes
From: Rob Stewart (robertstewart_at_[hidden])
Date: 2013-03-24 07:20:52

On Mar 23, 2013, at 12:13 PM, Alexander Lamaison <awl03_at_[hidden]> wrote:

> Beman Dawes <bdawes_at_[hidden]> writes:
> 
>> On Sat, Mar 16, 2013 at 12:54 PM, Alexander Lamaison <awl03_at_[hidden]> wrote:
>>> 
>>> I'm manipulating Unix paths for use over SFTP, but doing so on Windows.
>>> For instance I might want to append "c" to the Unix path "/a/b".
>>> 
>>> path p("/a/b");
>>> p /= "c";
>>> cout << p.string();
>>> 
>>> In version 2 this would output "/a/b/c" but now it produces "/a/b\c".
>>> Why the breaking change?
>> 
>> IIRC, it was partially requests from users and partially the
>> realization that most users want platform independent syntax but platform dependent semantics.
> 
> In that case I'd expect it to output "\a\b\c".  I can't think of a
> reason why mixed slashes would ever be the right answer. It's the worst of both worlds.

You're expecting this line

   path p("/a/b");

to parse your string into "a" / "b" when it merely stores the string as you gave it. Otherwise, when you add this line

   p /= "c";

you expect the previous separator to be used rather than the native separator it uses.

> But, the biggest issue is that the change wasn't documented.  The docs make a big deal of the change from templated paths to a single path class, but make no mention of this, more significant, difference.

I can't imagine that Beman would reject a documentation patch.

>> If you would rather continue to use operator /= then change the output to
>> 
>>    cout << p.generic_string();
> 
> I've since discovered this string/generic_string/native triplet.  I don't think it's the right solution.  string() should either return the generic string or the native string.  What it returns at the moment is confusing and not very useful.  Or is there a use-case I'm not seeing.

string() is returning the contents, as you instructed path to form it. Calling generic_string() means parse the contents and ensure all separators follow the generic syntax.

To do what you want would require path to be modal. Marking it, in this case, to do everything in the generic format first would have given the behavior you wanted. However, there is no such modality. / appends with the native separator. Construction from a string, or appending one, merely stores the supplied string. When you want a specific format after mixing those operations, call generic_string() or native_string().

HTH

___
Rob

(Sent from my portable computation engine)