Re: Subroutines and '&'

Paul Lalli <mritty@xxxxxxxxx> wrote in comp.lang.perl.misc:
On Aug 8, 6:50 am, anno4...@xxxxxxxxxxxxxxxxxxxxxx wrote:
<tru...@xxxxxxxxx> wrote in comp.lang.perl.misc:
my $MODE=param('Mode');
{
no strict;
$MODE="GetLogin" unless $MODE; # default sub to execute
&$MODE; # else execute this sub
}

This saves a lot of 'if-else' chains. Just my 2 Canadian cents.

I don't see how it saves an "if". The "else..." comment is
misleading.
You are making sure that $MODE points to a sub, and *then*
(not "else") you're executing it.

I'm assuming he meant it prevents the need for something like:
if ($MODE eq 'Foo') {
Foo();
} elsif ($MODE eq 'Bar') {
Bar();
} else {
GetLogin();
}

Really, he's talking about Symrefs here, which is not at all the same
issue as using an & or not on a subroutine.

Right, that makes sense. It would still be preferable to use a dispatch
table (untested):

my %func = map {
no strict 'refs';
( $_ => \ &{ $_ });
} qw( Foo Bar Baz);

my $mode = param( 'Mode');
( $func{ $mode} || \ &GetLogin)->()

That way the symrefs are restricted to the table setup where they will
only be used with the code-determined qw( Foo Bar Baz). Whatever
value $mode has at run time, only these functions or GetLogin will
be called. The original code could call anything an attacker happens
to know about.

Anno
.

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