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// Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
part of dart.ffi;
/// The supertype of all FFI union types.
/// FFI union types should extend this class and declare fields corresponding
/// to the underlying native union.
/// Field declarations in a [Union] subclass declaration are automatically
/// given a setter and getter implementation which accesses the native union's
/// field in memory.
/// All field declarations in a [Union] subclass declaration must either have
/// type [int] or [double] and be annotated with a [NativeType] representing the
/// native type, or must be of type [Pointer]. For example:
/// ```c
/// typedef union {
/// int a;
/// float b;
/// void* c;
/// } my_union;
/// ```
/// ```dart
/// class MyUnion extends Union {
/// @Int32()
/// external int a;
/// @Float()
/// external double b;
/// external Pointer<Void> c;
/// }
/// ```
/// All field declarations in a [Union] subclass declaration must be marked
/// `external`. You cannot create instances of the class, only have it point to
/// existing native memory, so there is no memory in which to store non-native
/// fields. External fields also cannot be initialized by constructors since no
/// Dart object is being created.
/// Instances of a subclass of [Union] have reference semantics and are backed
/// by native memory. The may allocated via allocation or loaded from a
/// [Pointer], but cannot be created by a generative constructor.
abstract class Union extends _Compound {
/// Construct a reference to the [nullptr].
/// Use [UnionPointer]'s `.ref` to gain references to native memory backed
/// unions.
Union() : super._();
Union._fromTypedDataBase(Object typedDataBase)
: super._fromTypedDataBase(typedDataBase);