Assignment of data-member in read-only structure, class in STL set

Question

The minimal example of the problem I\'m having is reproduced below:

#include 
using namespace std;

class foo {
public:
  int value, x;
  foo(const in         


        

Answer 1

Given that the "x" variable is not involved in the less-than comparison, it would be safe in this case to make "x" mutable, allowing you to modify it from within the set. Your class definition would then become:

class foo {
public:
  int value;
  mutable int x;

  foo(const int & in_v) : value(in_v), x(0) { }
  bool operator<(const foo & rhs) const {
    return value < rhs.value; 
  }
};

And you can now use it in the std::set and modify x as you like. In this case it is pointless to keep two copies of the data structure as the previous poster has suggested.