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Subject: Re: [boost] [filesystem] Request for commentsonproposedrelative()function
From: Yakov Galka (ybungalobill_at_[hidden])
Date: 2014-05-18 13:21:18

On Sun, May 18, 2014 at 6:02 PM, Peter Dimov <lists_at_[hidden]> wrote:

> Yakov Galka wrote:
> ...
> On second thought though, I'm not sure that this is what I'd want from
> usability point of view. When the user gives me "c:a", he probably wants
> "c:a" and not "c:/x/a", even if the documentation states that paths are
> treated relative to "c:/x".
> ...
> "c:/x" / "/a" == "/a"
> "d:/x" / "/a" == "/a"
> for the same usability reasons.

I don't follow. The real-world use-case is that I have some
config/project/database/install-dir named x = "c:/myproduct", that
references another file y, conceptually relative to itself. I think we all
agree that if y = "a.txt" then x / y = "c:/myproduct/a.txt" is the desired
result. Now, if y = "/windows/a.txt" I would definitely expect the result
to be "c:/windows/a.txt", and not "/windows/a.txt" which may end up
resolved to "d:/windows/a.txt" if "d:" is the current drive. How "/abc" is
any different from "a.txt" in this respect?

> In this case, both z1 and z2 are absolute (even though they are not
> absolute by the N3940 definition.)

OK, went through N3940 (as I said, wasn't following it for some time). The
problem of the definition

> A path that unambiguously identifies the location of a file without
reference to an additional starting location.

is that it is unclear what 'location' is (a path or an inode?) and that it
lacks a quantifier. After 10 minutes trying to understand what it says, I
think that this is what it tried to say:

    x is absolute iff for all possible filesystem instances F (under the
given OS), if exists a filesystem node f in F and a program state S such
that f = open(F, S, x), then for all program states S, f = open(F, S, x).

(i.e. ∀F ∃f ∈ F ((∃S f = open(F,S,x)) → (∀S f = open(F,S,x)))) Here open(F,
S, x) is the node of F that the path x resolves to at the program state S,
and program state S includes current directory, environment vars, etc...


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