Re^2: Uses for an lvalue subroutine

Oh, the joys of lvalue!

    package Object;

    use vars '$AUTOLOAD';

    # :

    sub AUTOLOAD : lvalue
    {
            my ($self) = shift;

            $AUTOLOAD =~ s/.*://;

            @_? $self->{$AUTOLOAD} = shift : $self->{$AUTOLOAD} ||= undef;
    }

Sweet candy. Now you can do stuff like this:

     my ($object) = new Object;

     $object->whatever = "Data";
     print "Whatever is '",$object->whatever,"'\n";

It "goes both ways" as an LVALUE, and this AUTOLOAD routine has backwards compatibility with the older, somesay wacky function method:

     my ($object) = new Object;

     $object->whatever("Data");
     print "Whatever is '",$object->whatever(),"'\n";

You even get warnings with perl -w if you use uninitialized members.

Comment on Re^2: Uses for an lvalue subroutine Download Code

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Re: Re: Re: Uses for an lvalue subroutine by chipmunk (Parson) on Jan 10, 2001 at 09:02 UTC
That's twisted and clever. One question: what is the intent of the `\|\|= undef`, other than changing `$self->{$AUTOLOAD}` to `undef` if it's `0` or `""`? `my ($object) = new Object; $object->whatever(0); print "Whatever is '",$object->whatever(),"'\n"; # Oops!` [download]	[reply] [d/l] [select]
Re^4: Uses for an lvalue subroutine by tadman (Prior) on Jan 11, 2001 at 02:14 UTC
chipmunk points out something that I had failed to test for. In my effort to reduce the code down to a minimum, that case slipped right through my logic. Here's Take II, new and improved support for 0 and "" added: sub AUTOLOAD : lvalue { my ($self) = shift; $AUTOLOAD =~ s/.*://; @_? $self->{$AUTOLOAD} = shift : !defined($self->{$AUTOLOAD})? $self->{$AUTOLOAD} = undef : $self->{$AUTOLOAD}; } The reason for having `$self->{$AUTOLOAD} = undef` is to give the caller something to assign to. Returning an invalid hash entry will cause an assignment error. 'undef' is not a valid lvalue, but returning a reference to a variable which may have a value of 'undef' is acceptable. BTW, I've never had to indent my '?:'s before, but it was the only way to make how this worked clear(er).	[reply] [d/l]