Hello everyone, I'm doing some comparing between the usage of class and module. I declare a class named Foo with a instance method called hello as the following:

1  package Foo;
2 
3  __PACKAGE__->hello('test1');
4  hello('test2');
5
6  sub hello {
7     my ($self, $arg) = @_;
8    print "hello=". $arg. "\n";
9  }
10 1;
[download]

And the result is like this:

arg=test1
Use of uninitialized value $arg in concatenation (.) or string at line
+ 8
[download]

I am a bit confused by the usage of __PACKAGE__. In terms of the result, I guess line3 is calling a object method but don't see any new() syntax. Looks like line4 is calling a regular subroutine and that's why the error happens. Am I right about this?

Under which kind of situation should we use __PACKAGE__ to create an object instead of calling its new() in the caller program?

Thank.