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Asked: 2026-05-11T08:27:53+00:00

I thought it was odd that C# let me call sort on my class

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I thought it was odd that C# let me call sort on my class and not specify a way to sort them nor write a compare overload. When i ran this code this error popped up

List<MyClass> myClassArray= new List<MyClass>(); //myClassArray.add(...); myClassArray.Sort();  An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll  Additional information: Failed to compare two elements in the array.

Why does C# let me compile this code when it doesnt know how to sort this! -edit-

Codex ask why it does this. I wrote a theory on why it does it in my comments. Here some example code.

class A : IComparable<A> {     public int CompareTo(A a) { return 0; } } class C //: IComparable<A> {     public int CompareTo(A a) { return 0; } }     static void test()     {         A a = new A();         bool b;         C c = new C();          object o = a;         IComparable<A> ia = (IComparable<A>)o;         b = ia == ia;          o = c;         IComparable<A> ic = (IComparable<A>)o;         b = ic == ic;          //uncomment this to get a compile time error         //IComparable<A> ic2 = c;         return;     }

If you uncomment the line before return, you’ll get a compile time error. When you uncomment IComparable in class c, it will compile and work.

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1 Answer

  1. There’s no constraint on the generic parameter of List<T> requiring it to implement IComparable<T>. If there were, it would (sort of) guarantee that elements could be sorted, but you wouldn’t be able to use List<T> to hold anything that didn’t implement IComparable. And since you probably won’t be sorting every list you create, this is the right decision.

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