Difference between my $self = shift and my ($self) = @

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

Hello dear Monks! I just wanted to know - is there any REAL difference between following. Say, I do:

$bag->contents();
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And my subroutine is:

sub contents {
my $self = shift; # WHAT IF I CALL my ($self) = @_ ?
#so something
return;
}
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So, is there any real difference between my $self = shift and my ($self) = @_ Thanks!