$self is a hashref and __PACKAGE__ is the package in the class that it's in. If this code is in package "Foo", then the '_init' key in self is auto-incremented. The first time this occurs, it will evaluate as false, allowing Foo::_init to function, but subsequent calls will fail.

nysus wrote:

But how does throwing a class, {__PACKAGE__}, on the right side of an object method call, $self->{_init}, create an attribute?

You're simply auto-vivifying a hash key with the name being equal to the current package name. You see, Perl has an interesting shortcut for complex data structures. In this case, the following are equivalent:

$self->{_init}->{__PACKAGE__};
$self->{_init}{__PACKAGE__};
[download]

If you've dereferenced the first reference, you're allowed to drop the arrow notation for subsequent dereferences. Thus, $self->{_init} becomes a hashref on the fly by merely appending curly braces.

Cheers,
Ovid

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