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Postings from September 2015
On Fri, 11 Sep 2015 23:25:04 +0200, Aristotle Pagaltzis
<pagaltzis@gmx.de> wrote:
> * H.Merijn Brand <h.m.brand@xs4all.nl> [2015-09-10 17:45]:
> > $x ~~ 42 --> $x == 42 ???
> > $x ~~ "foo" --> $x eq "foo" ???
>
> In $x ~~ $y with $y eq 42 you cannot tell whether the user wanted the
> smartmatch to mean $x == 42 or $x eq 42. You can only tell that when the
> user has given you a literal 42 vs a literal '42'.
>
> So this can only work with literals. Therefore it would appear to be
> useless: $x ~~ 42 with a literal 42 will never mean anything other than
> $x == 42, so you can just as well write $x == 42 yourself. And it gets
> worse: $x eq 42 is shorter and easier to type than $x ~~ '42' !
>
> However, there is one case for it: if `when` is defined in terms of
> smartmatch, then these rules would allow writing e.g.
>
> given ($mode) {
> when ('enable') { ... }
> when ('disable') { ... }
> # ...
> }
>
> That’s syntax I don’t really want to lose, and it would be nicer to say
> that `when (EXPR)` is sugar for `if ($_ ~~ EXPR) { ...; break }` instead
> of making `when` have its own very special cases over and above what ~~
> does.
>
> Regards,
This given/when example is exactly why I added those two lines, and is
also why I have no problem with the corner case being invalid.
The (ridiculous) example I have in real life is a perl script that acts
as a 'lp' wrapper for HP printers that is 2900 lines long (including
the full documentation so I can ship it as a single file) and has a
foreach my $opt (@opt_o) {
given ($opt) {
when ("A4") {
}
when (/^(?: tra?y ([0-9]))$/x) {
}
with 50 "when" entries and only string and regex cases.
--
H.Merijn Brand http://tux.nl Perl Monger http://amsterdam.pm.org/
using perl5.00307 .. 5.21 porting perl5 on HP-UX, AIX, and openSUSE
http://mirrors.develooper.com/hpux/ http://www.test-smoke.org/
http://qa.perl.org http://www.goldmark.org/jeff/stupid-disclaimers/
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