class Counter
{
private:
    int x;
public:
    Counter(int x) : x(x) {}
    const int GetX(void) const { return x; }
    void SetX(const int x) { this->x = x; }
    void Increase(void) { x++; }
};

void LogCounterShouldImmutable(Counter &c)
{
    c.Increase();
    cout << "Counter value: " << c.GetX() << endl;
}

void LogCounterImmutable(const Counter &c)
{
    cout << "Counter value: " << c.GetX() << endl;
}

test1.cpp(18) : error C2662: 'Counter::Increase' : cannot convert 'this' pointer from 'const Counter' to 'Counter &'
    Conversion loses qualifiers

public class ImmutableContainer<T>
{
    private readonly T obj;
    public ImmutableContainer(T obj) { this.obj = obj; }
    public T Obj { get { return obj; } }
}

private void LogCounterImmutable(ImmutableContainer<Counter> container)
{
    Console.WriteLine("Counter value should be {0}.", container.obj.X);
    container.obj.Increase();
    Console.WriteLine("Counter value changed to {0}.", container.obj.X);
}

public interface IReadOnlyCounter
{
    int X { get; }
}

public class Counter : IReadOnlyCounter
{
    public int X { get; set; }
    public Counter(int x) { this.X = x; }
    public void Increase() { X++; }
}

private void LogCounterImmutable(IReadOnlyCounter counter)
{
    Console.WriteLine("Counter value should be {0}.", counter.X);
}

public interface IReadOnlyCounter
{
    int X { get; }
    void Log();
}

public class Counter : IReadOnlyCounter
{
    public readonly IReadOnlyCounter constThis = (IReadOnlyCounter)this;
    public int X { get; set; }
    public Counter(int x) { this.X = x; }
    public void Increase() { X++; }
    public void Log() {
        Console.WriteLine(constThis.X);
    }
}

private void LogCounterImmutable(IReadOnlyCounter counter)
{
    Console.WriteLine("Counter value should be {0}.", counter.X);
    counter.Log();
}