Reference Loop detected erroneously

[pkimike]

Source/destination types

class RootClass {
    public String Name { get; set; }
    public Int32 Number { get; set; }

    public override Boolean Equals(Object obj) {
        return ReferenceEquals(this, obj) || obj is RootClass other && Equals(other);
    }
    protected Boolean Equals(RootClass other) {
        return String.Equals(Name, other.Name, StringComparison.OrdinalIgnoreCase) && Number == other.Number;
    }
    public override Int32 GetHashCode() {
        unchecked {
             return (StringComparer.OrdinalIgnoreCase.GetHashCode(Name) * 397) ^ Number;
        }
    }
}

class ChildContainerClass : RootClass {
    public List<ChildEntryClass> Entries { get; set; } = new List<ChildEntryClass>();
}

class ChildEntryClass : RootClass {
    public String MyProperty { get; set; }
}

Source/destination JSON

Not applicable

Expected behavior

Object serializes properly

Actual behavior

Exception thrown unless ReferenceLoopHandling.Serialize is passed to force

Steps to reproduce

var container = new ChildContainerClass() {
    Name = "My",
    Number = 1
};
var entry = new ChildEntryClass {
    Name = "My",
    Number = 1
};
container.Entries.Add(entry);
Console.WriteLine("Instance Equals  : " + container.Equals(entry)); // returns True, because they equal by implementation
Console.WriteLine("Reference Equals : " + ReferenceEquals(container, entry)); // returns False, because they are different refs
var str = JsonConvert.SerializeObject(container); // will fail with reference loop exception

[elgonzo]

This is not a bug. Using equality comparison for detecting circular references is intended default behavior. For example, see this comment from the author of the library: #401 (comment). (Mostly because this behavior has already been established over a span of numerious library versions across many years before people started asking for a change of this behavior. But at that point breaking compatibility by breaking established default behavior was deemed not acceptable anymore. Unfortunate, but understandable and reasonable...)

Fortunately, you can override this behavior by configuring Newtonsoft.Json's EqualityComparer setting to use object reference equality comparison only:

JsonConvert.DefaultSettings = () => new JsonSerializerSettings
{
    EqualityComparer = ReferenceEqualityComparer.Instance
};

var str = JsonConvert.SerializeObject(container);

[pkimike]

Thanks for the clarification.