http://www.perlmonks.org?node_id=617883


in reply to Re: [Perl 6] Any provision for a "dereferencing object"?
in thread [Perl 6] Any provision for a "dereferencing object"?

In perl5, what about something like...
my $a = []; $a->[1]{bar}{baz}[3] = 7; bless $a, "hrmph"; *hrmph::deref = sub { $_[0]->[1]{bar}{baz}[3] }; print "yeah: ", $a->deref, "\n";

It's maybe not the clearest or most maintainable thing in the whole wide world, but it's not "impossible." You could even build on it to make it more readable, reliable, and more flexible in various ways.

(UPDATE: I clicked the wrong reply button, so if there's a kind editor that could move me up a level?)

UPDATE: Oh, I see what you're up to I think. Some function you build once and applicate anwhere. I am also a little surprised your $x->$deref.

-Paul

Replies are listed 'Best First'.
Re^3: [Perl 6] Any provision for a "dereferencing object"?
by blazar (Canon) on May 28, 2007 at 21:47 UTC

    In perl5, what about something like...

    my $a = []; $a->[1]{bar}{baz}[3] = 7; bless $a, "hrmph"; *hrmph::deref = sub { $_[0]->[1]{bar}{baz}[3] }; print "yeah: ", $a->deref, "\n";

    Well, that's not quite the same thing, because you create a method for each "dereferencing chain". I was talking about putting it e.g. in some scalar or in an aggregate. But now that you got me thinking, this is certainly possible and even easier than what you wrote:

    my $x = []; $x->[1]{bar}{baz}[3] = 7; bless $x, "whatever"; my $deref = sub { $_[0]->[1]{bar}{baz}[3] }; print "yeah: ", $x->$deref, "\n";

    What's even more interesting is that the variable appearently doesn't need to be blessed at all, which I wouldn't have known nor suspected without trying. In fact the following works just the same too:

    my $x = []; $x->[1]{bar}{baz}[3] = 7; # bless $x, "whatever"; my $deref = sub { $_[0]->[1]{bar}{baz}[3] }; print "yeah: ", $x->$deref, "\n";
    It's maybe not the clearest or most maintainable thing in the whole wide world, but it's not "impossible."

    Well, what I wrote -literally- is still impossible: that is precisely to have a "dereferencing chain" as a self sustained "single entity", existing in and of itself without a reference to be applied to. In fact here we have a cheap workaround that is perfectly equivalent. Yet it's not, from the "philosophical" POV, exactly the same thing.

Re^3: [Perl 6] Any provision for a "dereferencing object"?
by blazar (Canon) on May 29, 2007 at 14:40 UTC
    UPDATE: Oh, I see what you're up to I think. Some function you build once and applicate anwhere. I am also a little surprised your $x->$deref.

    Well, that's a bit of common OO syntactical sugar: if $code contains a subref, then in

    $object->$code(@args);

    the corresponding sub is called as a method on $object. This is often used to implement callbacks in a way that personally I like:

    $object->record( name => 'doit', callback => sub { my $caller=shift; # ... } );