C#•2y ago

✅ Is there a way you can check if an object’s equality operator will compare by reference?

I want to implement a data validation attribute like [UniqueValues] for ASP.NET model binding which will basically just call .Distinct() and check the count against the original list.

This however won’t work with plain classes, only value types, records, or classes that implement IEquatable. Is there a way I can check an

object

object

instance to see if it will be compared by reference, and if so throw an exception?

dreadfullydistinctOP•2/22/24, 6:06 PM

To clarify I want the attribute to operate on a list

jcotton42•2/22/24, 6:29 PM

I would just require IEquatable<T>
Pretty sure records have that interface

dreadfullydistinctOP•2/22/24, 6:41 PM

Hmm I guess then you have to have the attribute be

[UniqueValues<T>]
public List<T> Property

Angius•2/22/24, 7:32 PM

Or just check

Angius•2/22/24, 7:33 PM

Ah, does pattern matching work with open generics, that's the question...

dreadfullydistinctOP•2/22/24, 7:50 PM

I don’t think so based on a quick sharplab

dreadfullydistinctOP•2/22/24, 7:50 PM

I wonder if you could use reflection to check that it implements that interface

dreadfullydistinctOP•2/22/24, 7:51 PM

Open generics might work there

dreadfullydistinctOP•2/23/24, 1:23 PM

Went with IEquatable<TElement> because we wanted to pattern match the input is an enumerable to call Distinct, and it turns out ‘is IEnumerable<object>’ doesn’t work even with covariance

dreadfullydistinctOP•2/23/24, 1:24 PM

Thanks @jcotton42 :thumbsupsmiley:

dreadfullydistinctOP•2/23/24, 1:24 PM

?close

dreadfullydistinctOP•2/23/24, 1:24 PM

Erm