Comparing two structs using ==

Question

I am trying to compare two structs using equals (==) in C#. My struct is below:

public struct CisSettings : IEquatable<CisSettings>
{
    public int Gain { get; private set; }
    public int Offset { get; private set; }
    public int Bright { get; private set; }
    public int Contrast { get; private set; }

    public CisSettings(int gain, int offset, int bright, int contrast) : this()
    {
        Gain = gain;
        Offset = offset;
        Bright = bright;
        Contrast = contrast;
    }

    public bool Equals(CisSettings other)
    {
        return Equals(other, this);
    }

    public override bool Equals(object obj)
    {
        if (obj == null || GetType() != obj.GetType())
        {
            return false;
        }

        var objectToCompareWith = (CisSettings) obj;

        return objectToCompareWith.Bright == Bright && objectToCompareWith.Contrast == Contrast &&
               objectToCompareWith.Gain == Gain && objectToCompareWith.Offset == Offset;

    }

    public override int GetHashCode()
    {
        var calculation = Gain + Offset + Bright + Contrast;
        return calculation.GetHashCode();
    }
}

I am trying to have struct as a property in my class, and want to check to see if the struct is equal to the value I am trying to assign it to, before I go ahead and do so, so I am not indicating the property has changed when it hasn't, like so:

public CisSettings TopCisSettings
{
    get { return _topCisSettings; }
    set
    {
        if (_topCisSettings == value)
        {
            return;
        }
        _topCisSettings = value;
        OnPropertyChanged("TopCisSettings");
    }
}

However, on the line where I check for equality, I get this error:

Operator '==' cannot be applied to operands of type 'CisSettings' and 'CisSettings'

I can't figure out why this is happening, could somebody point me in the right direction?

Answer 1

You need to overload the == and != operators. Add this to your struct:

public static bool operator ==(CisSettings c1, CisSettings c2) 
{
    return c1.Equals(c2);
}

public static bool operator !=(CisSettings c1, CisSettings c2) 
{
   return !c1.Equals(c2);
}

Answer 2

When you override the .Equals() method, the == operator is not automatically overloaded. You need to do that explicitly.

See also Guidelines for Overriding Equals() and Operator == or CA1815: Override equals and operator equals on value types.

Answer 3

You don't implement explicitly an equality operator, so == is not defined particularly for the type.

Answer 4

You should overload your operator is some way like this:

public static bool operator ==(CisSettings a, CisSettings b)
{
    return a.Equals(b);
}