sub t1{ return "t1:",\&t1; }
sub t2{ undef *t2 if @_; return "t2:",\&t2; }

print t1(), t2();
t1: CODE(0x1bd5200) t2: CODE(0x1bd5410)

print t1(), t2();
t1: CODE(0x1bd5200) t2: CODE(0x1bd5410)

print t1(), t2(), t2('change it');
t1: CODE(0x1bd5200) t2: CODE(0x1bd5410) t2: CODE(0x1bd52d8)