fix(docs): the documented 'metal' delegate throws unconditionally

MIGRATION_V2_TO_V3.md

@@ -36,8 +36,22 @@ The `delegate` parameter has been renamed to `delegates` and now accepts an **ar
 ```
 
 ```diff
-- const model = useTensorflowModel(source, 'metal')
-+ const model = useTensorflowModel(source, ['metal'])
+- const model = useTensorflowModel(source, 'core-ml')
++ const model = useTensorflowModel(source, ['core-ml'])
+```
+
+### The `'metal'` delegate is not implemented
+
+`'metal'` is still part of the `TensorflowModelDelegate` union, but it has no
+implementation - creating a model with it throws
+`The Metal Delegate ("metal") is not implemented!`
+(see [`cpp/TfliteHelpers.cpp`](./cpp/TfliteHelpers.cpp), `getMetalDelegate()`).
+It is documented as deprecated on the `TensorflowModelDelegate` type. On Apple
+platforms, use `'core-ml'` instead:
+
+```diff
+- const model = useTensorflowModel(source, ['metal'])
++ const model = useTensorflowModel(source, ['core-ml'])
 ```
 
 ### The `'default'` delegate is removed

README.md

@@ -12,7 +12,7 @@ A high-performance [TensorFlow Lite](https://www.tensorflow.org/lite) library fo
 - 💨 Zero-copy ArrayBuffers
 - 🔧 Uses the low-level C/C++ TensorFlow Lite core API for direct memory access
 - 🔄 Supports swapping out TensorFlow Models at runtime
-- 🖥️ Supports GPU-accelerated delegates (CoreML/Metal/OpenGL)
+- 🖥️ Supports hardware-accelerated delegates (CoreML on iOS, GPU/NNAPI on Android)
 - 📸 Easy [VisionCamera](https://github.com/mrousavy/react-native-vision-camera) integration
 
 ## Migrating from v2

cpp/TfliteHelpers.cpp

@@ -147,7 +147,9 @@ TfLiteDelegate* getCoreMLDelegate() {
 }
 
 TfLiteDelegate* getMetalDelegate() {
-  throw std::runtime_error("Metal Delegate is not yet supported!");
+  throw std::runtime_error("The Metal Delegate (\"metal\") is not implemented! "
+                           "Use \"core-ml\" on Apple platforms, or \"android-gpu\"/\"nnapi\" on "
+                           "Android instead.");
 }
 
 TfLiteDelegate* getNNAPIDelegate() {

example/ios/Podfile

@@ -15,7 +15,6 @@ if linkage != nil
 end
 
 $EnableCoreMLDelegate=true
-$EnableMetalDelegate=true
 
 target 'TfliteExample' do
   config = use_native_modules!

src/loadTensorflowModel.ts

@@ -22,7 +22,7 @@ const tfliteModule =
  * * If you are passing in a `{ url: ... }`, make sure the URL points directly to a `.tflite` model. This can either be a web URL (`http://..`/`https://..`), or a local file (`file://..`).
  *
  * @param source The `.tflite` model in form of either a `require(..)` statement or a `{ url: string }`.
- * @param delegates The delegates to use for computations. Uses the standard CPU delegate per default. The `core-ml` or `metal` delegates are GPU-accelerated, but don't work on every model.
+ * @param delegates The delegates to use for computations. Pass an empty array (`[]`) to use the standard CPU delegate. The `core-ml` (iOS), `android-gpu` and `nnapi` (Android) delegates are hardware-accelerated, but don't work on every model.
  * @returns The loaded Model.
  */
 export async function loadTensorflowModel(

src/specs/Tflite.nitro.ts

@@ -1,5 +1,14 @@
 import type { HybridObject } from 'react-native-nitro-modules'
 
+/**
+ * A hardware-accelerating delegate to run the TFLite model with.
+ *
+ * - `'core-ml'`: CoreML (Apple platforms). Requires `$EnableCoreMLDelegate`.
+ * - `'nnapi'`: NNAPI (Android)
+ * - `'android-gpu'`: GPU (Android)
+ * - `'metal'`: **deprecated, not implemented** - creating a model with this
+ *   delegate always throws. Use `'core-ml'` on Apple platforms instead.
+ */
 export type TensorflowModelDelegate =
   | 'metal'
   | 'core-ml'

src/useTensorflowModel.ts

@@ -24,7 +24,7 @@ export type TensorflowPlugin =
  * * If you are passing in a `{ url: ... }`, make sure the URL points directly to a `.tflite` model. This can either be a web URL (`http://..`/`https://..`), or a local file (`file://..`).
  *
  * @param source The `.tflite` model in form of either a `require(..)` statement or a `{ url: string }`.
- * @param delegates The delegates to use for computations. Uses the standard CPU delegate per default. The `core-ml` or `metal` delegates are GPU-accelerated, but don't work on every model.
+ * @param delegates The delegates to use for computations. Pass an empty array (`[]`) to use the standard CPU delegate. The `core-ml` (iOS), `android-gpu` and `nnapi` (Android) delegates are hardware-accelerated, but don't work on every model.
  * @returns The state of the Model.
  */
 export function useTensorflowModel(
@@ -50,7 +50,7 @@ export function useTensorflowModel(
     }
     load()
     // JSON.stringify compares delegates by value so inline array literals
-    // (e.g. ['core-ml', 'default']) don't cause the effect to re-run every render
+    // (e.g. ['core-ml']) don't cause the effect to re-run every render
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [source, JSON.stringify(delegates)])