using an object as a variable type

Honoured bretheren in Perl

I am trying to create a constrained variable using syntax like this ...

use threads;
use threads::shared;
my $var : shared;
[download]

To keep things simple I have created a package called Me providing a 'Me' object. Now I want to be able to do something like this.

use Me;
my $user : Me;
$user = "Random"; # this is OK
$user = "Deterministic"; # croaks
[download]

Here is the Me.pm

#!/usr/bin/perl
use strict;
use warnings;

package Me;
use Carp;
use overload '""' => \&str;

sub new {
    my ($class, $value) = @_;
    validate ($value) if defined $value;
    bless \$value, $class;
}

sub validate {
    my $value = shift;
    my @names = qw (Random_Walk Random Walk);
    croak "$value is not a good name\n" unless grep {$value eq $_} @na
+mes;
}

sub str {"Not telling you"};
1;
[download]

It works fine like this

> perl -Mlib=. -MMe -le'my $m = new Me (Random);print $m'
Not telling you
> perl -Mlib=. -MMe -le'my $m = new Me (Determined);print $m'
Determined is not a good name
 at -e line 1
# But I can not suss out how to get his to work
> perl -Mlib=. -MMe -le'my $m : Me; $m = "Random"; print $m'
Invalid SCALAR attribute: Me at -e line 1
[download]

I have had a look into attributes and found this Invalid SCALAR attribute? but I remain completely unenlighted how to use this to get the threads::shared syntax working or even if it is possible without delving into XS

Cheers,
R.

Pereant, qui ante nos nostra dixerunt!

Comment on using an object as a variable type Select or Download Code
Re: using an object as a variable type by Anonymous Monk on Jan 27, 2006 at 14:00 UTC
"using an object as a variable type" sounds like nonsense :) perldoc -f eval	[reply]
Re^2: using an object as a variable type by Random_Walk (Parson) on Jan 27, 2006 at 14:25 UTC
Not sure how the title is nonsense, I wish to constrain the behaviour of the variable to that defined in the 'Me' object so is the package not providing the type of the variable ? I am trying to do this using the syntax of threads::shared which I guess is instantiating a threads::shared object and assigning it to the given variable name. I can live with what I have now `my $m = new Me (Random);` but out of curiosity and to improve my Perl foo I want to discover and emulate how `my $val : shared` works. Not sure how eval can help me here, I don't want to trap the errors, I am intending to enforce limits on the varaiable and croak if an attempt is made to assign an illegal value to it. Cheers, R. Pereant, qui ante nos nostra dixerunt!	[reply] [d/l] [select]
Re^3: using an object as a variable type by chromatic (Archbishop) on Jan 27, 2006 at 20:49 UTC
I am trying to do this using the syntax of threads::shared which I guess is instantiating a threads::shared object and assigning it to the given variable name. That's not what it does. It ties the variable in such a way that multiple threads can access it. That's not what the attribute syntax does though; attributes just run a specific piece of code just after Perl compiles the statement. That code can do anything.	[reply]
Re^2: using an object as a variable type by Anonymous Monk on Jan 27, 2006 at 15:04 UTC
perldoc attributes `1. Code: package Canine; package Dog; my Canine $spot : Watchful ; Effect: use attributes (); attributes::->import(Canine => \$spot, "Watchful");` [download]	[reply] [d/l]
Re: using an object as a variable type by phaylon (Curate) on Jan 27, 2006 at 14:57 UTC
You might want to read up on perldoc attributes and Attribute-Handlers. hth, p Ordinary morality is for ordinary people. -- Aleister Crowley	[reply] [d/l]


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using an object as a variable type

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