Override equality comparision for record struct

[FLAMESpl]

In record classes we can override equality comparision by implementing duck typed public bool Equals(<type_name>? other) method.
This approach does not work for structs, unit test in this snippet will fail:

public class Test
{
    private class Class
    {
        public int Id { get; }

        public Class(int id)
        {
            Id = id;
        }
    }

    private record struct Record(Class Class)
    {
        public bool Equals(Record? other)
        {
            if (other is null) return false;
            return other.Value.Class.Id == Class.Id;
        }
    }

    [Fact]
    public void MyTest()
    {
        var rec1 = new Record(new Class(0));
        var rec2 = new Record(new Class(0));
        Assert.Equal(rec1, rec2);
    }
}

How to override equality comparision for struct records?

[yaakov-h]

Take the ? out of public bool Equals(Record? other). Since this is a record struct, Record? is Nullable<Record> so the method does not have the correct signature to be the correct Equals(Record) method.

[Joe4evr]

To elaborate: The method signature public bool Equals(<type_name>? other) isn't strictly duck-typed - it comes from the fact that IEquatable<type_name> is implicitly placed on record declarations. Including the ? on value types makes your method just another overload instead of matching the IEquatable signature which is why it hasn't stopped the compiler from synthesizing its own Equals implementation.

[FLAMESpl]

ok, thanks it seems that for some reason my Rider IDE generates declaration with question mark

[yaakov-h]

sounds like a bug in Rider, it’s probably expecting a record class rather than a record struct.