Problems with map(function, array)

[Redei]

I'm puzzling over the use of map with user-defined functions. Here's some sample code:

sub my_uc {
    my $c = shift;
    return uc($c);
}

my @a = ('a'..'c');

@a = map { uc($_) } @a;
print "==>@a<== { uc(\$_) }\n";

@a = map { my_uc($_) } @a;
print "==>@a<== { my_uc(\$_) }\n";

@a = map uc, @a;
print "==>@a<== uc,\n";

@a = map my_uc, @a;
print "==>@a<== my_uc,\n";

The output is:

==>A B C<== { uc($_) }
==>A B C<== { my_uc($_) }
==>A B C<== uc,
==>  <== my_uc,

Apparently Perl doesn't support the syntax map function, array for user-defined functions. Or perhaps with this syntax it expects to find the function's argument in $_. So here's my second try:

sub my_new_uc {
    my $c = shift // $_;
    return uc($c);
}

sub my_uc {
    my $c = shift;
    return uc($c);
}

my @a = ('a'..'c');

@a = map my_new_uc, @a;
print "==>@a<== my_new_uc,\n";

@a = map my_uc, @a;
print "==>@a<== my_uc,\n";

@a = map my_new_uc, @a;
print "==>@a<== my_new_uc,\n";

Surprisingly, my new function sometimes works, and sometimes not. Here's the output from that second code fragment:

==>A B C<== my_new_uc,
==>  <== my_uc,
==>  <== my_new_uc,

The information on map in perlfunc doesn't say anything about using your own functions except in the form map { function($_) } @array and I couldn't find any help in other tutorials or FAQs. Does anyone know what is happening in my second example, and why $_ sometimes is used in map and sometimes not?