How to use a custom comparer for EqualityComparer<T>.Default?

Question

Note: my case is for byte[] but I believe a good answer would work for any type.

Visual Studio's auto-generated implementation of Equals uses EqualityComparer<T>.Default.Equals(T x, T y) for reference types. I have a lot of classes with byte arrays that needs to be included in Equals so I'd like to keep Visual studio's code if possible but Default returns a ObjectEqualityComparer for byte arrays. I've written a simple byte array comparer but I'm not sure how to proceed to have it used instead of ObjectEqualityComparer.

public class Foo
{
    public int Id {get;set;}
    public byte[] Data {get;set;}

    public override bool Equals(object obj)
    {
        var foo = obj as Foo;
        return foo != null &&
            Id == foo.Id &&
            EqualityComparer<byte[]>.Default.Equals(Data, foo.Data);
    }
}

static void Main
{
    Foo f1 = new Foo { Id = 1, Data = new byte[1] { 0xFF } };
    Foo f2 = new Foo { Id = 1, Data = new byte[1] { 0xFF } };
    bool result = f1.Equals(f2); // false
}

public class ByteArrayComparer
{
    public bool Equals(byte[] x, byte[] y)
    {
        return x.SequenceEqual(y);
    }

    public int GetHashCode(byte[] obj)
    {
        return obj.GetHashCode(); 
        // as Servy said, this is wrong but it's not the point of the question, 
        // assume some working implementation
    }
}

Should ByteArrayComparer implement IEqualityComparer, inherit from EqualityComparer and override the methods, or something else?

Answer 1

Create and use an instance of your custom comparer instead of using EqualityComparer<byte[]>.Default in your class:

public class Foo
{
    public int Id { get; set; }
    public byte[] Data { get; set; }

    private readonly ByteArrayComparer _comparer = new ByteArrayComparer();

    public override bool Equals(object obj)
    {
        var foo = obj as Foo;
        return foo != null &&
            Id == foo.Id &&
            _comparer.Equals(Data, foo.Data);
    }
}

You may also want to implement IEqualityComparer<T> and GetHashCode() in your ByteArrayComparer class. EqualityComparer<T>.Default returns an instance of a class that implements this interface, but I assume you don't want to use this one as you have implemented your own custom comparer.

How to use the IEqualityComparer