Boxed.Mapping Unity3D support

[Razenpok]

Describe the feature

I want to use Boxed.Mapping in my Unity project, but it uses Expression.Lambda.Compile from System.Linq.Expressions here. Since compiling the game to mobile platforms requires AOT compiling, Unity forbids the usage of this method. Is it really necessary there? Is it possible to switch to plain new()?

[RehanSaeed]

This is a performance enhancement. I ran the benchmark in the project with all the versions of .NET the project supports and its still faster using the factory as opposed to new().

Can we solve your problem by using an #if '#else` pre-processor directive to use new in this case? What is the target framework used by unity? Perhaps we can target that directly?

[Razenpok]

Wow, I did not expect that these compile shenanigans beat the plain new()

The NuGet packages are available in Unity via this mirror registry. It simply downloads the .nupkg files and repacks them in a Unity-compatible format. It always takes .NETStandard2.0/.NETStandard2.1 dlls from the package, hence there is a whitelist in this repo to only provide Unity-compatible packages that don't use restricted stuff like Expression.Lambda.Compile.

Maybe you can #if #else the constructor part and publish a new Boxed.Mapping.Unity ( or Boxed.Mapping.UnityCompat or whatever) package?

[RehanSaeed]

new() is pretty slow. It uses reflection under the covers.

Hmmm, I'm not familiar with Unity and was hoping it would have its own unity target framework instead of netstandard2.1. I'm not sure how I can detect this and switch to a different code path.

[Razenpok]

Uhh, "new() uses reflection under the covers" part sounds super counter-intuitive. Where do I read more about it?

Regarding switching to a different code path: I don't think there's a way to detect Unity in runtime, but you can wrap the code in a #if UNITY and compile with this define symbol turned on (and publish a separate NuGet package)

#if UNITY
    public static T CreateInstance() => new T();
#else
    public static T CreateInstance() => CreateInstanceFunc();
#endif

[RehanSaeed]

Oh excellent, #if UNITY was exactly what I was looking for.

I actually got help from none other than Jon Skeet:

https://stackoverflow.com/questions/46500630/how-to-improve-performance-of-c-sharp-object-mapping-code

[Razenpok]

Thanks for the link!

For the record, #if UNITY is not something Unity-related, you might just as well write #if I_DONT_WANT_SPEED and it would do the same thing

[RehanSaeed]

Looks like there are some defined by Unity but they're not going to help us.

https://docs.unity3d.com/560/Documentation/Manual/PlatformDependentCompilation.html

Having another NuGet package is a fair bit of extra work to support.

[Razenpok]

Can I help with that? To me, it looks like a two-step task:

1. Wrap the conflicting code in #if UNITY
2. Duplicate Boxed.Mapping.Unity.csproj (with UNITY directive enabled) from Boxed.Mapping.csproj and put it in the same folder

From what I see, your build pipeline requires no tweaks to support new packages. And I suppose there won't be any code changes in the future that would break Unity compatibility, so the support effort should be negligible?

[RehanSaeed]

Ok sure.