Re: [boost] [filesystem] Request for commentsonproposedrelative()function

Subject: Re: [boost] [filesystem] Request for commentsonproposedrelative()function
From: Peter Dimov (lists_at_[hidden])
Date: 2014-05-18 11:02:57

Yakov Galka wrote:

...

> > z1 = "/a"
> > z2 = "c:a"

...

> Is z2 absolute? Wrt. what definitions?
>
> * "Definition 1" (x / "c:" = "c:" for all x), and either yours or mine 
> (equivalent) definitions of is_absolute: then z2 is absolute because x / 
> z2 = z2 for all x. Then my claim that path of max-rank (here rank(drive)) 
> is absolute is true.
>
> * "Definition 2", ("c:" / x / "c:" = "c:" / x ...): you cannot define 
> ranks for such concatenation. If you give ranks to elements you get a 
> stronger framework, which, in particular, is associative.

At first, I was in favor of definition 2, stated as "x / y is the meaning of 
y when the current directory is x".

    "c:/x" / "c:a" == "c:/x/a"
    "d:/x" / "c:a" == "c:a"

    "c:/x" / "/a" == "c:/a"
    "d:/x" / "/a" == "d:/a"

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".

In addition, "x" / "c:a" is not representable.

Definition 1, then.

    "c:/x" / "c:a" == "c:a"
    "d:/x" / "c:a" == "c:a"

But then

    "c:/x" / "/a" == "/a"
    "d:/x" / "/a" == "/a"

for the same usability reasons.

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