Have I implemented Equals()/GetHashCode() correctly?

Question

The program was working with this implementation:

class Instrument
{
    public string ClassCode { get; set; }
    public string Ticker { get; set; }
    public override string ToString()
    {
        return " ClassCode: " + ClassCode + " Ticker: " + Ticker + '.';
    }
}

But because I need to use Instrument in Dictionary I've decided to implement equals/hashcode:

class Instrument
{
    public string ClassCode { get; set; }
    public string Ticker { get; set; }
    public override string ToString()
    {
        return " ClassCode: " + ClassCode + " Ticker: " + Ticker + '.';
    }

    public override bool Equals(object obj)
    {
        if (obj == null)
            return false;

        Instrument instrument = obj as Instrument;
        if (instrument == null)
            return false;

        return ((ClassCode.Equals(instrument.ClassCode)) && (Ticker.Equals(instrument.Ticker));
    }

    public override int GetHashCode()
    {
        int hash = 13;
        hash = (hash * 7) + ClassCode.GetHashCode();
        hash = (hash * 7) + Ticker.GetHashCode();
        return hash;
    }
}

Now the program has stopped working. In such or similar places I receive "KeyNotFoundException":

if (cache.Keys.Any(instrument => instrument.Ticker == newTicker && instrument.ClassCode == newClassCode))

Is it possible that some pieces of the code assume that equals and hashcode IS NOT implemented? Or probably I just implemented them wrong? Sorry I'm not familiar with such advanced features in C# as the last piece of code and don't know how it is connected with equals or hashCode.

Answer 1

Your HashCode and Equals methods should depend only on immutable properties - your implementation uses ClassCode and Ticker which both have setters and are therefore mutable.