What's happening under the covers in Component.Transform?

[iron pike]

Greetings, I'm hoping someone from Unity can clarify something I've been pondering.

In Unity 5, Unity added this optimization:

If you decompile the transform property you see that it is a wrapper for an external C++ native code GetTransform() method.
So I'm wondering what exactly is happening in that GetTransform() method.
You can see this in this IL snippet that rotates a transform:

    .method public hidebysig
        instance void MyMethod2 () cil managed
    {
        // Method begins at RVA 0x2826
        // Code size 27 (0x1b)
        .maxstack 8
 
        // base.transform.Rotate(0f, 0f, 0f);
        IL_0000: ldarg.0
        IL_0001: call instance class [UnityEngine.CoreModule]UnityEngine.Transform [UnityEngine.CoreModule]UnityEngine.Component::get_transform()
        IL_0006: ldc.r4 0.0
        IL_000b: ldc.r4 0.0
        IL_0010: ldc.r4 0.0
        IL_0015: callvirt instance void [UnityEngine.CoreModule]UnityEngine.Transform::Rotate(float32, float32, float32)
        // }
        IL_001a: ret
    } // end of method ForIL::MyMethod2

[dapper hazel]

Are you decompiling Unity?

[iron pike]

So my question is: What exactly is happening in GetTransform()? I am assuming that if Unity is caching the transform component "on the c# side" that means they've made a copy of a struct or something? It seems that everytime we access the transform we are making a C++ native call to get whatever this "cached" object is? Are they marshaling a struct into a C# transform?
Help me understand what magic is happening here 🙂

Thanks

[iron pike]

What? No! That is the IL from a C# method call that rotates a transform. However, if you hover over the transform property in your IDE and hit F12, it will show you the decompiled C# code for the transform property:

  /// <summary>
  ///   <para>Base class for everything attached to GameObjects.</para>
  /// </summary>
  [RequiredByNativeCode]
  [NativeClass("Unity::Component")]
  [NativeHeader("Runtime/Export/Scripting/Component.bindings.h")]
  public class Component : Object
  {
    /// <summary>
    ///   <para>The Transform attached to this GameObject.</para>
    /// </summary>
    public extern Transform transform { [FreeFunction("GetTransform", HasExplicitThis = true, ThrowsException = true), MethodImpl(MethodImplOptions.InternalCall)] get;
}

[hollow widget]

That quote is either just outdated or incorrect. It's cached on the native side.

We don't know the specific about how exactly they are caching it

[iron pike]

That's what I thought but I'm trying to get confirmation because I product Unity game dev tutorials and I don't want to publish inaccurate information. I'm hoping someone from Unity will chime in on this.

[hollow widget]

This would have been a good question to ask on the last Dev Blitz Day. Outside of those, it's unlikely you're going to get an answer from anyone at Unity.

[dapper hazel]

My bad for jumping into conclusions. But yeah that ^ and you could ask in the forums as well so it doesn't get lost in here

[hollow widget]

There's a discussion about this, including that quote, here:
https://forum.unity.com/threads/cache-transform-really-needed.356875/

[dapper hazel]

I see very little activity from Unity staff here unless its one of the events

[iron pike]

Thanks!