Re: Overload of operator[]

From:
"Bo Persson" <bop@gmb.dk>
Newsgroups:
comp.lang.c++
Date:
Tue, 26 Feb 2008 18:48:19 +0100
Message-ID:
<62j1mpF238dhfU1@mid.individual.net>
Adrian wrote:

I was trying to create a "readonly" operator[] in public scope and a
"write" operator[] in private scope of the class. But the compiler
seem intent on trying to use the private version.

Am I expecting to much from the compiler or is it not possible for
it to resolve the correct version of the function.

TIA

Adrian

dluadrianc:/home/adrianc> g++ -Wall -ansi -pedantic scope.cc
scope.cc: In function 'int main(int, char**)':
scope.cc:17: error: 'int& Container::operator[](size_t)' is private
scope.cc:31: error: within this context

#include <iostream>
#include <vector>

class Container : private std::vector<int>
{
  public:
     const int &operator[](size_t i) const
     {
        return (this->operator[](i));
     }
     using std::vector<int>::resize;
     void set(size_t t, int i)
     {
        this->operator[](t)=i;
     }
  private:
     int &operator[](size_t i)
     {
        return this->operator[](i);
     }
};

int main(int argc, char *argv[])
{
  Container a;

  a.resize(10);
  a.set(3,3);

  std::cout << "Read test\n";
  if(a[2]==3)
  {
     std::cout << "Its 3\n";
  }
  else
  {
     std::cout << "Its not 3\n";
  }

  return 0;
}


It will call the const version of the operator for const containers,
and the non-const version for non-const containers. Only after
selecting the best fit for an operator or a function call, does the
compiler check for access rights. Oops, can't call it because it is
private!

Bo Persson

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