in reply to smart match operator should be smarter!

First of all, what's with all the useless parens? 

my @numbers = (2);  =>  my @numbers = 2;
my @other = (2);    =>  my @other = 2;
@numbers ~~ (2)     =>  @numbers ~~ 2
my @empty = ();     =>  my @empty;

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my @numbers = 2; @numbers ~~ 2 being false is to be expected. It was necessary to make ~~ non-commutative to fix bugs. In this case, since you're comparing against a simple scalar, a scalar comparison is made. You want 2 ~~ @numbers.

As for when (()), it should give an error if it doesn't do anything useful. I'll see about reporting a bug. ( On second thought, empty list in scalar context returns undef. I don't think anything can be done about that. )

Finally, keep in mind that when you specify an array, it's a reference to the array that's provided to the match operator. 

>perl -E"@a = qw(a b); say @a ~~ 2 ? 'match' : 'no match'"
no match

>perl -E"@a = qw(a b); say @a ~~ (0+\@a) ? 'match' : 'no match'"
match

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The idea might be to allow the following 

>perl -E"@a = qw(a b); say \@a ~~ \@a ? 'match' : 'no match'"
match

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but it actually uses a different rule. 

>perl -E"@a = qw(a b); @b = qw(a b); say \@a ~~ \@b ? 'match' : 'no ma
+tch'"
match

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This might be improvable. I'll see about bringing this up too.

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Re^2: smart match operator should be smarter!
by 7stud (Deacon) on Nov 22, 2009 at 15:24 UTC

    Can you explain what those examples are supposed to demonstrate?

    What I got out of it is that the naive rule is:

    1) the match operator compares references.

    Therefore, if you smart match @arr ~~ 2, you are doing this:

    my @arr = (10, 20, 30);

my $aref = \@arr;
say $aref;   #ARRAY(0x1810e90)

0x1810e90 ~~ 2

--output:--
NOPE!

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    However, the naive rule breaks down here:

    
my @a = (10, 20, 30);
my @b = (10, 20, 30);

my $aref = \@a;
my $bref = \@b;

say $aref;
say $bref;

--output:--
ARRAY(0x1810e90)
ARRAY(0x181ace0)

#yet...

say @a ~~ @b ? 'yes' : 'no';

--output:--
yes

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    So you can't really say that the smart operator is comparing references, otherwise @a and @b would not match.

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[d/l]
[select]

      Like I said, it's a different rule (ARRAY ~~ ARRAY instead of ANY ~~ NUM).

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