c++11 - C++ operator [] -

i trying implement operator [] used once set , once get, need differentiate between 2 cases, in case of get, need throw exception if returned value equal -1; whereas in case of set overwrite value. appple[2] = x; y=apple[2];

i dont know how differentiate between 2 modes, function signature is:

   double& security::operator[](quartertype index){     if(index<0 || index>max_quaters){         throw listexceptions::quarteroutofbound();     }     return evaluation[index].getvalueaddress();    } 

c++ not allow distinction of

appple[2] = x;  y=apple[2]; 

the common solution return proxy object:

struct appleproxy {    security & obj;     unsigned index;     appleproxy(security &, unsigned) : ... {}     operator double()   // getter    {       return obj.getat(index);    }     operator=(double rhs)    {       obj.setat(index, rhs);    } }  appleproxy operator[](unsigned index) { return appleproxy(*this, index); } 

proxy require significant attention detail, i've omitted const correctness, life-time management, taking-the-address-of (double & x = apple[2]; x = 17;), etc.

due pitfalls, tend avoid them.