Why shouldn't I use UNIVERSAL::isa?

Question

According to this

http://perldoc.perl.org/UNIVERSAL.html

I shouldn\'t use UNIVERSAL::isa() and should instead use $obj->isa() or CLASS->isa().

This means

Answer 1

See the docs for UNIVERSAL::isa and UNIVERSAL::can for why you shouldn't do it.

In a nutshell, there are important modules with a genuine need to override 'isa' (such as Test::MockObject), and if you call it as a function, you break this.

I have to say, my $self = shift if UNIVERSAL::isa($_[0], __PACKAGE__) doesn't look terribly clean to me - anti-Perl advocates would be complaining about line noise. :)