Constants and compiler optimization in C++

void someType::somefunc();

void MyFunc()
{
    someType A(4);   //
    Fling(A.m_val);
    A.someFunc();
    Flong(A.m_val);
}

class Test
{
public:
  Test (int value) : m_value (value)
  {
  }

  void SetValue (int value) const
  {
    const_cast <Test&>(*this).MySetValue (value);
  }

  int Value () const
  {
    return m_value;
  }

private:
  void MySetValue (int value)
  {
    m_value = value;
  }

  int
    m_value;
};

void modify (const Test &test, int value)
{
  test.SetValue (value);
}

void main ()
{
  const Test
    test (100);

  cout << test.Value () << endl;
  modify (test, 50);
  cout << test.Value () << endl;
}

100
50

volatile const

#include <iostream>
using namespace std;

void swap (const int &a, const int &b)
{
  int
    c = a;
  const_cast <int&>(a) = b;
  const_cast <int&>(b) = c;
}

void main ()
{
  const int a = 10;
  const int b = 20;
  int c = 30;
  swap (a,b);
  cout << "a = " << a << endl;
  cout << "b = " << b << endl;
  swap (c,b);
  cout << "b = " << b << endl;
  cout << "c = " << c << endl;
}

a = 10;
b = 20;

b = 20;

c = 10;

void f(Type dont_modify); // or
void f(Type const& dont_modify);