You're right, use re 'eval' is not absolutely required, and I shouldn't have said it like that. But beware! Your example code works fine on just an instance-by-instance basis. But if you want to do this programatically and extensibly, then my warning about closure-ing lexicals applies. It's tricky to make a generic-use sub that does this kind of matching.
You may be tempted to do the following, but it won't work:
sub match_all_ways {
my ($string, $regex) = @_;
my $count;
my $incr = qr/(?{$count++})/;
$string =~ /(?:$regex)$incr(?!)/;
return $count;
}
print match_all_ways("abcdef", qr/..*..*./); # 20
print match_all_ways("abcdef", qr/..*..*./); # undef
It's because the qr// object is compiled just once and always refers to the first instance of $count. If you call this sub more than once, you will always get undef.
You have to do something ugly like this to get around it:
sub match_all_ways {
use vars '$count';
my ($string, $regex) = @_;
local $count = 0;
my $incr = qr/(?{$count++})/;
$string =~ /(?:$regex)$incr(?!)/;
return $count;
}
or this
{
my $count;
my $incr = qr/(?{$count++})/;
sub match_all_ways {
my ($string, $regex) = @_;
$count = 0;
$string =~ /(?:$regex)$incr(?!)/;
return $count;
}
}
So yes, it can be done programatically without use re 'eval', but it's non-trivial and a little messy ;)
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