Comparing generic fields

Question

I have some generic types, like the following:

public struct Tuple<T1, T2> { ... }
public struct Tuple<T1, T2, T3> { ... }
etc.

These should in theory be able to compare themselves against other values of the same type, so that I can write the following type of code:

List<Tuple<Type, String>> l = new List<Tuple<Type, String>>();
l.Add(new Tuple<Type, String>(typeof(ISomeInterface), "123"));
if (l.Contains(new Tuple<Type, String>(typeof(ISomeOtherInterface), "123"))
    ...

unfortunately, there was a bug in my code, and the question then becomes how to do this correctly.

The bug had to do with my implementation of CompareTo>, which basically looks like this:

Int32 result = HelperMethods.CompareTwoFields<T1>(_Value1, other._Value1);
if (result != 0)
    return result;

Int32 result = HelperMethods.CompareTwoFields<T2>(_Value2, other._Value2);
if (result != 0)
    return result;

return 0;

HelperMethods.CompareTwoFields looks like this:

internal static Int32 CompareTwoFields<T>(T field1, T field2)
{
    Int32 result = 0;
    if (ReferenceEquals(field1, null) != ReferenceEquals(field2, null))
        result = ReferenceEquals(field1, null) ? -1 : +1;
    else if (!ReferenceEquals(field1, null) && field1 is IComparable<T>)
        result = ((IComparable<T>)field1).CompareTo(field2);
    else if (!typeof(T).IsValueType)
    {
        if (Object.ReferenceEquals(field1, field2))
            return 0;
        else
            return field1.ToString().CompareTo(field2.ToString());
    }
    return result;
}

The last if-statement there is something I tucked on now to fix the bug, but is this correct?

Basically, how do I compare two Type objects? Is there a meaningful comparison for these, except just to convert them to a string and compare?

Answer 1

Do you mean:

bool equal = EqualityComparer<T>.Default.Equals(val1,val2);

This works with IEquatable<T> (for T : IEquatable<T>), else falls back to object.Equals.

There is also Comparer<T>.Default for inequality comparisons (greater/less):

int delta = Comparer<T>.Default.Compare(val1,val2);

This uses T : IComparable<T>, or T : IComparable otherwise.

By the way, Type should just use the regular reference compare provided by object.Equals, so it should just work fine with the above.