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Postings from November 2012
On 19.11.2012 18:17, sp@smartspb.net (via RT) wrote:
> Successfull match $_[0] =~ /foo(.+)/ inside subroutine
> overrides $_[0] if subroutine called as foo($1).
>
> ###### script ###### sp@uskr:~/3 (1570) cat u.pl
> use strict; use warnings; use feature qw(:all);
>
> sub foo {
> say ' before =~ $_[0] is ', "'$_[0]'";
> $_[0] =~ /foo(.+)/;
> say ' after =~ $_[0] is ', "'$_[0]'", ' and $1 is ', "'$1'";
> }
>
> # ok
>
> say 'call foo("foo123");';
> foo('foo123');
>
> # at least strange
>
> say 'call foo($1);';
> 'barfoo123' =~ /(foo.+)/ && foo($1);
>
> ###### output ###### sp@uskr:~/3 (1571) perl u.pl
>
> call foo("foo123");
> before =~ $_[0] is 'foo123'
> after =~ $_[0] is 'foo123' and $1 is '123'
> call foo($1);
> before =~ $_[0] is 'foo123'
> after =~ $_[0] is '123' and $1 is '123'
>
> sp@uskr:~/3 (1572)
>
> ###### summary ######
>
> I'm not sure is that bug or feature.
> I could not find something describing such things in docs.
This is not a bug. Quoting perldoc perlsub:
Any arguments passed in show up in the array @_ . Therefore, if you
called a function with two arguments, those would be stored in $_[0] and
$_[1] . The array @_ is a local array, but its elements are aliases for
the actual scalar parameters. In particular, if an element $_[0] is
updated, the corresponding argument is updated (or an error occurs if it
is not updatable). If an argument is an array or hash element which did
not exist when the function was called, that element is created only
when (and if) it is modified or a reference to it is taken. (Some
earlier versions of Perl created the element whether or not the element
was assigned to.) Assigning to the whole array @_ removes that aliasing,
and does not update any arguments.
--
Lukas Mai <l.mai@web.de>
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