Smart match operator support in Strawberry perl 5.10.0.1

jds17 has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am using the latest Strawberry perl 5.10.0.1 and although 5.10.0.1 > 5.10, the smart match operator does not seem to be supported. The following code lines come from feature.pm:

my %feature = (
    switch => 'feature_switch',
    say    => "feature_say",
    state  => "feature_state",
);
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So, no smart match here. Of course I get the error

Feature "~~" is not supported by Perl 5.10.0 at ...
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when trying "use feature '~~';". It seems to be partially working, though, even if I don't declare the usage. E.g. the following test program:

use feature qw / say /;
@a = (1, 17, 4);
say "first match succeeds" if (@a ~~ 17);
say "second match fails" unless ((1, 17, 4) ~~ 17);
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Prints out

first match succeeds
second match fails
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I would really like to use the smart match operator, too. Do you know when this will be fully supported in Strawberry Perl or if I overlooked something?

Comment on Smart match operator support in Strawberry perl 5.10.0.1 Select or Download Code

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Re: Smart match operator support in Strawberry perl 5.10.0.1 (array vs. list) by almut (Canon) on May 22, 2008 at 10:24 UTC
It seems to be partially working, though (I'm reading that that you would like it to match in the list case `(1, 17, 4) ~~ 17`, too.) I think it doesn't treat arrays and lists the same way (from "Smart matching in detail" in perlsyn): `$a $b Type of Match Implied Matching Code ====== ===== ===================== ============= ... Array Num array contains number grep $_ == $b, @$a ...` [download] If you have a list instead of an array, it interprets it in scalar context, i.e. it just uses the last element, here 4: `say "second match succeeds" if ((1, 17, 4) ~~ 4);` [download] I personally find this somewhat counterintuitive, too, but I suspect the language designers have had their reason to make it behave that way...	[reply] [d/l] [select]
Re^2: Smart match operator support in Strawberry perl 5.10.0.1 (array vs. list) by jds17 (Pilgrim) on May 22, 2008 at 15:57 UTC
Hi, thanks for your replies, did not have time to check them up to now! So it seems like I don't need to say "use feature '~~';" at all, that's o.k. On the other hand, I find the distinction made in the current context between a literal list and an array variable having the same list as value counterintuitive and it is the first time I have tripped over such a distinction in Perl. I never thought of the last element of a list to represent in some way the value of the list, which obviously happens in the smart match context as shown in almut's last example. I played a little more around with this and found that such a distinction is not made in case we are dealing with array references: `use feature qw / say /; sub check_match { $n++; my $expr = shift; say ("$n th match" . (eval($expr) ? ' succeeds' : ' fails')); } @a = (1, 17, 4); check_match('@a ~~ 17'); check_match('(1, 17, 4) ~~ 17'); $b = [1, 17, 4]; check_match('$b ~~ 17'); check_match('[1, 17, 4] ~~ 17');` [download] results in the following output: `1 th match succeeds 2 th match fails 3 th match succeeds 4 th match succeeds` [download] Now I am really puzzled, I would find it more natural if either both of cases 2 and 4 succeeded or both failed.	[reply] [d/l] [select]
Re: Smart match operator support in Strawberry perl 5.10.0.1 by moritz (Cardinal) on May 22, 2008 at 09:20 UTC
I don't know about Strawberry, but in vanilla perl 5.10.0 you can use smart matching without any `use feature` directive. This was wrongly documented in older development versions, but should be fixed now. (If it isn't, please tell us where you read that). `$ perl5.10.0 --version This is perl, v5.10.0 built for i486-linux-gnu-thread-multi [...] $ perl5.10.0 -wle 'print "YaY" if "a" ~~ m/./' YaY` [download] Update: I found the doc patch that fixed perlsyn.	[reply] [d/l] [select]
Re: Smart match operator support in Strawberry perl 5.10.0.1 by Khen1950fx (Canon) on May 22, 2008 at 10:17 UTC
I'm new to the smart match operator, but I took a stab at it. Does this help? `#!/usr/bin/perl use strict; use warnings; use 5.010; my @a = (1, 17, 4); say "first match suceeds" if (@a ~~ 17); say "second match fails" unless ([1, 17, 4] ~~ 17);` [download]	[reply] [d/l]