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.