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Marking the function call operator as const is beneficial, but insufficient, because data members with the mutable storage class specifier may still be modified within a const member function.

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Compliant Solution (std::reference_wrapper)

This compliant solution wraps uses std::ref to wrap the predicate in a std::reference_wrapper<T> object, ensuring that copies of the wrapper object all refer to the same underlying predicate object.

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
  
class MutablePredicate : public std::unary_function<int, bool> {
  size_t timesCalled;
public:
  MutablePredicate() : timesCalled(0) {}

  bool operator()(const int &) {
    return ++timesCalled == 3;
  }
};
 
template <typename Iter>
void print_container(Iter b, Iter e) {
  std::cout << "Contains: ";
  std::copy(b, e, std::ostream_iterator<decltype(*b)>(std::cout, " "));
  std::cout << std::endl;
}
 
void f() {
  std::vector<int> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
  print_container(v.begin(), v.end());

  MutablePredicate mp;
  v.erase(std::remove_if(v.begin(), v.end(), std::ref(mp)), v.end());
  print_container(v.begin(), v.end());
}

The above compliant compliant solution demonstrates using a reference wrapper over a functor object but can similarly be used with a stateful lambda. The code produces the expected results, where only the third element is removed.

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Using a predicate function object that contains state can produce unexpected values.

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

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