Calling .GetHashCode() on instances of empty structs doesn't return the same value in il2cpp builds

Unity Engine
,
1

Hey there, I just encounter something that feels like a bug.

Let’s say we have an empty struct :

public struct EmptyStruct
{
}

If we create two instances of this struct and store them in two different variables :

var emptyStruct1 = new EmptyStruct();
var emptyStruct2 = new EmptyStruct();

I would expect .Equals to be true between them and thus .GetHashCode() returning the same value :

Debug.Log($"Are Empty StructGetHashCode the same ? {emptyStruct1.GetHashCode() == emptyStruct2.GetHashCode()}");
Debug.Log($"Are EmptyStruct Equals ? {emptyStruct1.Equals(emptyStruct2)}");

It turns out everything is fine in Editor and in Mono Build.

Are EmptyStruct GetHashCode the same ? True
Are EmptyStruct Equals ? True

But …

When I build the project with IL2CPP, .Equals() still is true, but their .GetHashCode() returns different values, which seems contradictory to the classic Equals/GetHashCode usage.

Are EmptyStruct GetHashCode the same ? False
Are EmptyStruct Equals ? True

This behaviour is observed in Unity 2020.3.28f1 and also Unity 2021.2.15f1 on Android IL2CPP builds (and I think in all IL2CPP builds).

Ugly ways to ‘fix’ this involve overriding .GetHashCode() in the empty struct or just adding an unused field.

Is there something I miss ?

Just in case I created a bug report (https://fogbugz.unity3d.com/default.asp?1411455_rs5538034dq74a9l) and a colleague of mine recommended me to tag @JoshPeterson

Thank you all for your insights :slight_smile:

4 Likes
2

Update : it has been accepted in the Unity Issue Tracker, you can vote for it now :slight_smile:

3

We’ve corrected this issue internally - you should be notified via the bug report about it soon.

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