c# compare two generic values [duplicate]

Question

Possible Duplicate:
Can’t operator == be applied to generic types in C#?

I've coded something like this:

public bool IsDataChanged() {                T value1 = GetValue2;     T value2 = GetValue1();      return (valueInDB != valueFromView); } 

Right now the function doesn't compile with the error "Operator '!=' cannot be applied to operands of type 'T' and 'T'". What do I have to do to make this function work ?

Answer 1

You cannot use operators on generic types (except for foo == null which is special cased) unless you add where T : class to indicate it is a reference type (then foo == bar is legal)

Use EqualityComparer<T>.Default to do it for you. This will not work on types which only supply an operator overload for == without also either:

• implement IEquatable<T>
• overrides object.Equals()

In general implementing the == operator and not also doing at least one of these would be a very bad idea anyway so this is not likely to be an issue.

public bool IsDataChanged<T>() {                T value1 = GetValue2;     T value2 = GetValue1();      return !EqualityComparer<T>.Default.Equals(value1 , value2); } 

If you do not restrict to IEquatable<T> then the EqualityComparer default fallback may cause boxing when used with value types if they do not implement IEquatable<T> (if you control the types which are being used this may not matter). I am assuming you were using =! for performance though so restricting to the Generic type will avoid accidental boxing via the Object.Equals(object) route.

Answer 2

That should work for you.

public bool test<T>(T test, T test2) where T : class {     return (test != test2); } 

This is simply pasted from the examples that were commented on your question.