D:\>perl -Mwarnings -Moverload -e "use overload 'fu' => sub {return 1};"
overload arg 'fu' is invalid at -e line 1.

D:\>perl -Mwarnings -Moverload -e "use overload '&.' => sub {return 1};"

D:\>perl -Mwarnings -Moverload -e "use overload '&.=' => sub {return 1};"

D:\>