Duplicate Clone Functions v 7.0.2

[Austin Harris]

Getting duplicate clone helpers generated with the latest version.

Sample.fbs

attribute "fs_serializer";
attribute "fs_vector";
attribute "fs_valueStruct";
attribute "fs_unsafeExternal";

namespace DuplicateCloneHelpers;

struct B     (fs_valueStruct, fs_unsafeExternal:"System.Boolean") { data: bool; }
struct I8    (fs_valueStruct, fs_unsafeExternal:"System.SByte") { data: int8;}


union Primitive {
     B,
     I8,
}

Snip from FlatSharp.generated.cs showing the duplication.

namespace FlatSharp.Compiler.Generated
{
    internal static class CloneHelpers_011a996105fe4ccfbd87a7227c98bbdb
    {
        [global::System.Runtime.CompilerServices.MethodImplAttribute(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
        public static global::System.Boolean Clone(global::System.Boolean item)
        {
            checked
            {
                return item;
            }
        }

        [global::System.Runtime.CompilerServices.MethodImplAttribute(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
        public static global::System.Boolean Clone(global::System.Boolean item)
        {
            checked
            {
                return item;
            }
        }
        ...
    }
}

[James Courtney]

I can see how that would happen. What has possessed you to redefine the existing primitives? unsafeExternal was really intended for SIMD-accelerated types or other things FlatSharp doesn't support out of the box.

[James Courtney]

Oh, I see -- You're trying to get around the FlatBuffer Union restrictions by mapping primitive types externally. That's very clever and not something that I anticipated at all.

Clone methods are implemented "on the side" and work by overloading the "Clone" method so that the generated code doesn't have to be very smart. There's a Clone method available for every type in the object graph. For the dumb ones like primitives, strings, and value structs, they are just annotated with [MethodImpl(MethodImplOptions.AggressiveInlining)] so that it's functionally a copy. Since FlatSharp can't really resolve external types, it just knows that they are value structs so the Clone method gets implemented twice as you see.

The cheapest possible fix here is to just not emit clone methods at all for value structs since they are values. However, I need to actually revisit copy constructors wholesale at some point to remove some extra allocations. Let me noodle on this for a few days and get back to you on this thread.

Thanks for raising the issue!

[Austin Harris]

In the interim I have just copied the generated file out of the obj folder and removed the duplicate function definitions. It's working great so far with that workaround.

[James Courtney]

Just FYI -- I'm not in a big hurry to fix this. It seems like the workaround is pretty easy and this seems to be a pretty niche scenario, so I'm going to take the time and make sure I can do it correctly.