$class name not pass in the new()

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

In file Animals.pm, I have

package Cow;
sub Cow::speak {
    my $class = shift;
    print "$class Cow goes moooo!\n";
}

package Horse;
sub Horse::speak {
    my $class = shift;
    print "$class Horse goes neigh!\n";
}

package Sheep;
sub Sheep::speak {
    my $class = shift;
    print "$class Sheep goes baaaah!\n";
}

1;
[download]

And calling script works like this. first code can print value of $class and second code doesnt, why ??


Working code:

#!/usr/bin/perl

use lib '/home/perldood/Custom/perl/lib/perl5/Animals';
use Animals;

Cow->speak;
Horse->speak;
Sheep->speak;

Non working code:

#!/usr/bin/perl

use lib '/home/perldood/Custom/perl/lib/perl5/Animals';
use Animals;

Cow::speak;
Horse::speak;
Sheep::speak;

Can you please explain, Why ??
[download]

Thanks

Comment on $class name not pass in the new() Select or Download Code

Replies are listed 'Best First'.
Re: $class name not pass in the new() by chromatic (Archbishop) on Mar 12, 2012 at 07:01 UTC
These are function calls. The only arguments the functions receive are those you pass manually: `Cow::speak; Horse::speak; Sheep::speak;` [download] These are method calls. They receive their invocants as arguments, along with any arguments you pass manually: `Cow->speak; Horse->speak; Sheep->speak;` [download] You can call methods as functions, but you will break things if you do. Improve your skills with Modern Perl: the free book.	[reply] [d/l] [select]
Re^2: $class name not pass in the new() by perldood (Initiate) on May 11, 2012 at 19:32 UTC
Thanks guys !! Awesome explanation...	[reply]
Re: $class name not pass in the new() by Khen1950fx (Canon) on Mar 12, 2012 at 03:48 UTC
Intro to Objects by merlyn covers all the barnyard critters and pasture sounds. Give it another read.	[reply]
Re: $class name not pass in the new() by NetWallah (Canon) on Mar 12, 2012 at 04:03 UTC
If you "use warnings;" in the package, you get these helpful messages: `Use of uninitialized value $class in concatenation (.) or string at An +imal.pl line 7. Cow goes moooo! Use of uninitialized value $class in concatenation (.) or string at An +imal.pl line 13. Horse goes neigh! Use of uninitialized value $class in concatenation (.) or string at An +imal.pl line 19. Sheep goes baaaah!` [download] for the stuff you say is "Non working code". This gives a clear hint on what $class is set to when invoked that way, and why it "does not work". All great truths begin as blasphemies. ― George Bernard Shaw, writer, Nobel laureate (1856-1950)	[reply] [d/l]