c++ - How to control value assigned by operator [] -

i know how overload operator[] follows :

t& operator [](int idx) {     return thearray[idx]; }  t operator [](int idx) const {     return thearray[idx]; } 

but want control values assigned arr[i] = value. want control value between 0 , 9. there syntax so?

rene has provided answer. in addition this, here full example. note added "user-defined conversion", i.e., operator t, in proxy_t class.

#include <iostream> #include <array> #include <stdexcept>  template <class t> class myclass {     std::array<t, 5> thearray; // array...      class proxy_t     {         t& value; // reference element modified      public:         proxy_t(t& v) : value(v) {}          proxy_t& operator=(t const& i)         {             if (i >= 0 , <= 9)             {                 value = i;             }             else             {                 throw std::range_error(std::to_string(i));             }             return *this;         }          operator t() // required getting t value proxy_t, make cout-lines work         {             return value;         }     };  public:     proxy_t operator [](int const idx)     {         return thearray.at(idx);     }      t operator [](int const idx) const     {         return thearray[idx];     } };  int main() {     myclass<int> a;      std::cout << a[0] << std::endl;     a[0] = 2;     std::cout << a[0] << std::endl;     a[1] = 20; }