changes from code review

packages/mediapipe-core/lib/src/ffi_utils.dart

@@ -31,7 +31,7 @@ extension NativeStrings on String {
   ///
   /// See also:
   ///  * [toCharsPointerPointer]
-  Pointer<Char> toNative() => toNativeUtf8().cast<Char>();
+  Pointer<Char> copyToNative() => toNativeUtf8().cast<Char>();
 }
 
 /// Helpers to convert between a `List<String>` and a `Pointer<Pointer<Char>>`.
@@ -40,36 +40,39 @@ extension NativeListOfStrings on List<String> {
   ///
   /// See also:
   ///  * [Pointer<Char>.toNative] for a non-list equivalent.
-  Pointer<Pointer<Char>> toNative() {
+  Pointer<Pointer<Char>> copyToNative() {
     final ptrArray = calloc<Pointer<Char>>(length);
     for (var i = 0; i < length; i++) {
-      ptrArray[i] = this[i].toNative();
+      ptrArray[i] = this[i].copyToNative();
     }
     return ptrArray;
   }
 }
 
 /// Helpers to convert a [Pointer<Char>] into a [Uint8List].
 extension DartAwareChars on Pointer<Char> {
-  /// Creates a Dart view on a pointer to utf8 chars in native memory, cast as
-  /// unsigned, 8-bit integers. This method does not copy the data out of native
-  /// memory.
+  /// Creates a Dart view on native memory, cast as unsigned, 8-bit integers.
+  /// This method does not copy the data out of native memory.
   ///
-  /// If this is called on a `nullptr`, the method returns `null`.
-  Uint8List? toUint8List(int length) {
-    if (isNullPointer) return null;
+  /// Throws an exception if the method is called on a `nullptr`.
+  Uint8List toUint8List(int length) {
+    if (isNullPointer) {
+      throw Exception('Unexpectedly called `toUint8List` on nullptr');
+    }
     RangeError.checkNotNegative(length, 'length');
     return cast<Uint8>().asTypedList(length);
   }
 
   /// Converts the C memory representation of a string into a Dart [String].
   ///
-  /// If this is called on a `nullptr`, the method returns `null`.
+  /// Throws an exception if the method is called on a `nullptr`.
   ///
   /// See also:
   ///  * [toDartStrings]
-  String? toDartString({int? length}) {
-    if (isNullPointer) return null;
+  String toDartString({int? length}) {
+    if (isNullPointer) {
+      throw Exception('Unexpectedly called `toDartString` on nullptr');
+    }
     return cast<Utf8>().toDartString(length: length);
   }
 }
@@ -80,12 +83,14 @@ extension DartAwarePointerChars on Pointer<Pointer<Char>> {
   /// cast as a `List<String>`. This method does not copy the data out of native
   /// memory.
   ///
-  /// If this is called on a `nullptr`, the method returns `null`.
+  /// Throws an exception if the method is called on a `nullptr`.
   ///
   /// See also:
   ///  * [toDartString], for a non-list equivalent.
-  List<String?>? toDartStrings(int length) {
-    if (isNullPointer) return null;
+  List<String?> toDartStrings(int length) {
+    if (isNullPointer) {
+      throw Exception('Unexpectedly called `toDartStrings` on nullptr');
+    }
     final dartStrings = <String?>[];
     int counter = 0;
     while (counter < length) {
@@ -101,9 +106,11 @@ extension DartAwareFloats on Pointer<Float> {
   /// Creates a Dart view on a pointer to floats in native memory, cast as a
   /// Float32List. This method does not copy the data out of native memory.
   ///
-  /// If this is called on a `nullptr`, the method returns `null`.
-  Float32List? toFloat32List(int length) {
-    if (isNullPointer) return null;
+  /// Throws an exception if the method is called on a `nullptr`.
+  Float32List toFloat32List(int length) {
+    if (isNullPointer) {
+      throw Exception('Unexpectedly called `toFloat32List` on nullptr');
+    }
     RangeError.checkNotNegative(length, 'length');
     return cast<Float>().asTypedList(length);
   }
@@ -115,7 +122,7 @@ extension NativeFloats on Float32List {
   /// Copies a [Float32List] into native memory as a `float*`.
   ///
   /// Returns an [allocator]-allocated pointer to the result.
-  Pointer<Float> toNative({Allocator allocator = malloc}) {
+  Pointer<Float> copyToNative({Allocator allocator = malloc}) {
     final Pointer<Float> result = allocator<Float>(length)
       ..asTypedList(length).setAll(0, this);
     return result.cast();
@@ -128,7 +135,7 @@ extension NativeInts on Uint8List {
   /// Copies a [Uint8List] into native memory as a `char*`.
   ///
   /// Returns an [allocator]-allocated pointer to the result.
-  Pointer<Char> toNative({Allocator allocator = malloc}) {
+  Pointer<Char> copyToNative({Allocator allocator = malloc}) {
     final Pointer<Uint8> result = allocator<Uint8>(length)
       ..asTypedList(length).setAll(0, this);
     return result.cast();

packages/mediapipe-core/test/ffi_utils_test.dart

@@ -55,41 +55,41 @@ void main() {
 
   group('Strings should', () {
     test('be convertable to char*', () {
-      final Pointer<Char> abc = 'abc'.toNative();
+      final Pointer<Char> abc = 'abc'.copyToNative();
       calloc.free(abc);
     });
 
     test('be round-trippable', () {
-      expect('abc'.toNative().toDartString(), 'abc');
+      expect('abc'.copyToNative().toDartString(), 'abc');
     });
   });
 
   group('Lists of Strings should', () {
     test('be convertable to char**', () {
-      final Pointer<Pointer<Char>> strings = ['abc'].toNative();
+      final Pointer<Pointer<Char>> strings = ['abc'].copyToNative();
       calloc.free(strings);
     });
 
     test('be round-trippable', () {
-      expect(['abc'].toNative().toDartStrings(1), ['abc']);
+      expect(['abc'].copyToNative().toDartStrings(1), ['abc']);
     });
   });
 
   group('Uint8List should', () {
     test('be convertable to Pointer<Char>', () {
-      final Pointer<Char> ptr = Uint8List.fromList([1, 2, 3]).toNative();
+      final Pointer<Char> ptr = Uint8List.fromList([1, 2, 3]).copyToNative();
       malloc.free(ptr);
     });
 
     test('be round-trippable', () {
       expect(
-        Uint8List.fromList([1, 2, 3]).toNative().toUint8List(3).toList(),
+        Uint8List.fromList([1, 2, 3]).copyToNative().toUint8List(3).toList(),
         <int>[1, 2, 3],
       );
     });
 
     test('copy memory with toList', () {
-      final ptr = Uint8List.fromList([1, 2, 3]).toNative();
+      final ptr = Uint8List.fromList([1, 2, 3]).copyToNative();
       final List<int> ints = ptr.toUint8List(3).toList();
       calloc.free(ptr);
       expect(ints[0], 1);
@@ -101,13 +101,13 @@ void main() {
   group('Float32List should', () {
     test('be convertable to Pointer<Char>', () {
       final Pointer<Float> ptr =
-          Float32List.fromList([1.0, 2.0, 3.1]).toNative();
+          Float32List.fromList([1.0, 2.0, 3.1]).copyToNative();
       malloc.free(ptr);
     });
 
     test('be round-trippable', () {
       final doubles = Float32List.fromList([1.1, 2.2, 3.3])
-          .toNative()
+          .copyToNative()
           .toFloat32List(3)
           .toList();
       expect(doubles[0], closeTo(1.1, 0.0001));