On 2009-Aug-18, at 4:59 am, Carlin Bingham wrote:
2009/8/18 Timothy S. Nelson <wayl...@wayland.id.au>:
It's not in the revised spec, but I think that, even though
we've revived chdir, we should still have it so that changing $*CWD
will do a chdir under the hood.
While in the spirit of TIMTOWTDI, having a "magic" variable that
behaves differently from other variables when it's being set would
be rather odd.
But really, it isn't different.... After all, a "current path" IS
just a string; it's a string that shells helpfully insert for you at
certain points to save you some typing. The automatic insertion may
be "magical", but the string itself is quite ordinary.
The metaphor of being "in" a directory is quite fascinating, really.
Directories are not something you can be "in" -- they're lists that
hang on the walls of office buildings, or get printed on the pages of
a phone book. They're pointers, dir-ections to where you can find
something -- an office, a telephone, or a file on a disk. Literally
*on* the disk, not "in" it (disk platters are flat!). But this image
of working "in" a directory seems to come quite easily and naturally.
It wouldn't seem magical if we always wrote like this:
ls $PWD/foo/bar
PWD = $PWD/foo
ls $PWD/bar
That would still save a lot of typing, but not having to type the $PWD
saves even more.
But perhaps the apparent magic is that $*CWD = "/foo" sets the CWD to
"/foo", but setting it to "foo" does not set the CWD to "foo", but
rather to "$OLDCWD/foo". But that's not $*CWD's doing, that's our
path-quoting.
~ p[/foo/bar] eq "/foo/bar" # path literal cast to Str
~ p[foo/bar] eq "$CWD/foo/bar"
Not so strange to anyone familiar with the idea of relative paths, and
no more magical than... say, the fact that a literal series of digits
gets parsed as though it had an implicit "0d" in front of it. (Of
course, I suspect that $*CWD should be able to be set to a plain Str,
but the Str will be cast to an IO::Path because that's what
$*CWD.STORE() will take in its signature.)
-David
