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Simple OO

by lzcd (Pilgrim)
on Feb 12, 2002 at 06:47 UTC ( [id://144793]=perlquestion: print w/replies, xml ) Need Help??

lzcd has asked for the wisdom of the Perl Monks concerning the following question:

Ignoring complaints of cargo cult programming, can anybody shed light on why Perl doesn't seem to like this bit of code? It keeps looking for sheep.pm in the @INC and obviously not finding it. 
package sheep;
use strict;

sub new {
        my $proto=shift;
        my $class=ref{$proto} || $proto;
        my $self={};
        bless($self,$class);
        return $self;
}

sub bleet {
        my $self=shift;
        return 'Baaaa!';
}

package main;
use strict;
use sheep; 

my wolf=new sheep;
print wolf->bleet()."\n";

[download]

Replies are listed 'Best First'.
Re: Simple OO
by dws (Chancellor) on Feb 12, 2002 at 06:56 UTC
    If this code fragment is really in a single file, then you don't need   use sheep; Since the 'sheep' package is already in the symbol table. use is a bit confusing that way. The argument refers to a file, not a package. You have to trust that the file being use'd actually defines a package of the same name.

[reply]
[d/l]
[select]
      Without the use statement I get: 
      No such class wolf at demo.pl line 22, near "my wolf"
syntax error at demo.pl line 22, near "my wolf="

      [download]
[reply]
[d/l]

        You're missing some $'s ...

        my $wolf=new sheep;
print $wolf->bleet()."\n";

            --k.


[reply]
        Without the use statement I get: 
        No such class wolf at demo.pl line 22, near "my wolf"
syntax error at demo.pl line 22, near "my wolf="

        [download]
        The reason for this error message is a bit more obscure. (It has to do with something called "indirect object syntax".) However, the error goes away if turn the bareword wolf into the scalar $wolf. 
          my $wolf=new sheep;
     ^

        [download]
        I suspect this is what you had in mind.

[reply]
[d/l]
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Re: Simple OO
by Ryszard (Priest) on Feb 12, 2002 at 07:15 UTC
    Add this to the top of your test script (before you "use sheep") 
    BEGIN {push @INC, <path to sheep.pm>}

    [download]

    Interestingly enuff I had what seems to be a similar recently.

    HTH
[reply]
[d/l]
Re: Simple OO
by Biker (Priest) on Feb 12, 2002 at 08:03 UTC

    Do you use warnings?
    Do you use strict?

    Update: Of course you use strict. It's in the code snippet. Doh.
    What I really wanted to ask was about the warnings. The question about strict just went in there by habit. ;-)

    Everything will go worng!

[reply]
      Errr... yep to both.
[reply]
Re: Simple OO
by lzcd (Pilgrim) on Feb 12, 2002 at 07:31 UTC
    Once again, thank you all. I now have working sheep... err... yes.
[reply]
Re: Simple OO
by uwevoelker (Pilgrim) on Feb 12, 2002 at 17:13 UTC
    Shouldn't you use 
    my $class = ref($proto) || $proto;

    [download]
    Doesn't ref{$proto} return 'HASH'?
[reply]
[d/l]
Re: Simple OO
by mortis (Pilgrim) on Feb 13, 2002 at 05:46 UTC
    Minor point: don't use lowercase package names.

    Rationale: pragmas are lower case - your package name might class with a future pragma. Which is one of the reasons all (most) of the modules on CPAN start with uppercase characters .

[reply]

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