This project demonstrates a bug in using FSharp 4.1 with Unity 2017.3.0f3 and 2018.1.0b5.

I ran into a problem using FSharp's set collection and Set.contains with a struct type. It doesn't work when running under Unity. This project demonstrates the problem.

The Visual Studio solution includes a simple Unity project, a Library1 FSharp library, and an FSharp ConsoleApplication1.

The Library1 project includes a post-build task to copy FSharp.Core.dll and System.ValueTuple.dll into the Unity project's Assets/Plugins folder, as well as copy the test code in Library1.dll so that Unity can access it all.

Running the tests from the ConsoleApplication1 shows they all succeed in a non-Unity environment. Running the app from within the Unity Editor shows they fail.

I suspect the problem is with LanguagePrimitives.FastGenericComparer which for some reason does not work under Unity's version of the .NET 4.6 framework.

The master branch contains the files for Unity 2017.3.0f3 and the unity-2018.1.0b5 branch contains the files for that version. (There is no difference in code -- just changes applied by Unity during the version updgrade.)

Unity calls the .NET 4.6 support "experimental," so I would expect problems like this to occur, but it is still disconcerting.

The test code is in Library1/Library1.fs and should be pretty self explanatory.

There is a [<Struct>] record type called V3 which is a version of the type that first exhibted the problem in my own project. Thinking the problem had been introduced recently, I also tested the older form of struct types, and this one is called V3Struct.

Both types seem to exhibit the same behavior.

1. The Library1 projects needs a reference to UnityEngine.dll. You might have to Add reference and Browse to wherever your Unity Editor/Data/Managed folder is.

2. Because the Unity MonoBehaviour script in NewBehaviourScript.cs requires the FSharp Library1, the first successful build of the solution will fail. On a successful build of the Library1 project, the Library1.dll file (and supporting FSharp dlls) are copied into the Unity project. You have to give the Unity Editor a second to notice the changes, and then build again. At that point, the NewBehaviourScript.cs file will be able to find Library1.

3. You might have to right-click on ConsoleApplication1 and select Set as StartUp Project.

4. I don't know why Visual Studio copies UnityEngine.dll into the ConsoleApplication1` but it shouldn't be required and shouldn't affect things.

Right-click the ConsoleApplication1 in the Solution Explorer and select Set as StartUp project. Then click the > Start button on the toolbar.

Launch the Unity Editor and open the project folder. You might have to open the Main Scene asset in the Assets folder. The scene contains a GameObject which calls the FSharp code in its Start method.

The tests output messages to the Console tab.

Let me know if you run into problems.

Using Set.exists with a simple fun x -> x = y predicate instead of using Set.contains works fine. This implies that the comparer used for (=) is not the same as that used by the FastGenericComparer. I'm not sure if that implies the problem is with Unity's support of .NET 4.6, or with FSharp's implementation of FastGenericComparer.

In some of my tests (not shown), using an int * int * int tuple instead of the struct types shown here seemed to avoid the problem as well.