Stops fools from doing $obj = Class::new(...) when they should be doing $obj = new Class (...) or $obj = Class->new(...), or even $obj = Class::new(Class, ...).
This works in all but pathological cases such as: 
my $foo = Class->new( this => 2, that => 3 );
my $bar = Class::new( $foo => 4, that => 5 );

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where the first argument to the constructor (after the class name) is an object which isa-resolves to the package name. 
package Class;

sub new {
  unshift @_, __PACKAGE__
    unless $_[0]->isa(__PACKAGE__);
  # rest of code...
}

[download]

In reply to OO Slip-up Preventor by japhy

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