void overload_inc($V * object, SV * second, SV * switch) {
   /* code that adds 1 to the value held by object */ 
}

##</code><code>##

void overload_plus_eq(SV * object, SV * addon, SV * switch) {
   /*code that adds the value of addon to the value held by object */
}

##</code><code>##

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:\>