[tpm] Pub discussion (1)

[Alex Beamish]

Right -- but I have not yet encountered a situation where I want to
get things off the calling stack without actually moving the stack
pointer (that is, changing @_). I'm sure it's possible to cook
something up like that, but at that point it becomes more of an
intellectual exercise and not really something I'd find myself using
regularly.

Damian Conway's _Perl Best Practices_ (p. 180) says that you can use a
single list assignment (as I was espousing)

  my ( $foo, $bar, $baz ) = @_;

or a paragraph assignment

  my $foo = shift;
  my $bar = shift;
  my $baz = shift;

but that the list assignment is more 'concise' and enhances
readability. However (shudder) the paragraph version is fine when you
want to check input parameters as you get them off the stack, and make
suitable adjustments (using defaults, and so forth) as you go.

I'm a strong proponent of making things as readable and as compact as
possible (objectives that sometimes work against each other), hence my
preference for the list assignment. And, as has already been pointed
out, if you're making your choice based on performance, you're either
worrying needlessly ;) or using the wrong language.

Alex

On Fri, Aug 29, 2008 at 12:08 AM, Jim Harris <ja_harris at rogers.com> wrote:
> The variables get set the same either way.  The difference is that shift
> changes the value of @_, and the other way does not.
>
>
> --- On Fri, 8/29/08, Alex Beamish <talexb at gmail.com> wrote:
>
> From: Alex Beamish <talexb at gmail.com>
> Subject: [tpm] Pub discussion (1)
> To: "tpm" <tpm at to.pm.org>
> Received: Friday, August 29, 2008, 3:46 AM
>
> Greetings,
>
> After Madison's presentation on Net::DBus tonight, we retreated to
> Burgundy's where a number of interesting technical discussions popped
> up. Among them were discussions as to whether
>
>     my $self = shift;
>     my $value = shift;
>
> would mean changes to $self would be reflected the same way than if
> $self and
>  $value were collected in
>  one fell swoop using
>
>     my ( $self, $value ) = @_;
>
> My experiments consisted of three files, Obj1.pm:
>
> package Obj1;
>
> sub new
> {
>     my $class = shift;
>     my $self = {};
>
>     bless ( $self, $class );
>     return ( $self );
> }
>
> sub add
> {
>     my $self = shift;
>     my $value = shift;
>
>     $self->{value} = $value;
> }
>
> sub value
> {
>     my $self = shift;
>     return ( $self->{value} );
> }
>
> 1;
>
> And the almost identical Obj2.pm:
>
> package Obj2;
>
> sub new
> {
>     my $class = shift;
>     my $self = {};
>
>     bless ( $self, $class );
>     return ( $self );
> }
>
> sub add
> {
>     my ( $self, $value ) = @_;
>
>     $self->{value} = $value;
> }
>
> sub value
> {
>     my $self = shift;
>     return ( $self->{value} );
> }
>
> 1;
>
> And finally the test script:
>
> #!/usr/bin/perl
>  -w
> #
> #  Test creating
>  Obj1 and Obj2 to see if methods that access arguments
> #  differently affect whether changes propogate back to the caller.
> #  Specifically, does
> #
> #    my $self = shift;
> #    my ( $vars ) = @_;
> #
> #  produce a different result than
> #
> #    my ( $self, $vars ) = @_;
>
> use Obj1;
> use Obj2;
>
> {
>     my $obj1 = Obj1->new();
>     $obj1->add("This is object one");
>     print "Obj1 value is " . $obj1->value() . "\n";
>
>     my $obj2 = Obj2->new();
>     $obj2->add("This is object two");
>     print "Obj2 value is " . $obj2->value() . "\n";
> }
>
> The resulting output of running test12.pl is
>
> [alex at foo tpm-August2008]$ perl -w test12.pl
> Obj1 value is This is object one
> Obj2 value is This is object two
>
> This suggests that both methods (two shifts, or a single pull from @_)
> produce the same results.
>
> Have I misunderstood, or coded
>  something incorrectly? I believe
>  that
> both approaches mean pass by reference, meaning that changes are
> reflected.
>
> --
> Alex Beamish
> Toronto, Ontario
> aka talexb
> _______________________________________________
> toronto-pm mailing list
> toronto-pm at pm.org
> http://mail.pm.org/mailman/listinfo/toronto-pm
>



-- 
Alex Beamish
Toronto, Ontario
aka talexb