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expando.dart
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expando.dart
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// Copyright (c) 2012, 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.core;
/// An [Expando] allows adding new properties to objects.
///
/// Does not work on numbers, strings, booleans, `null`, `dart:ffi` pointers,
/// `dart:ffi` structs, or `dart:ffi` unions.
///
/// An `Expando` does not hold on to the added property value after an object
/// becomes inaccessible.
///
/// Since you can always create a new number that is identical to an existing
/// number, it means that an expando property on a number could never be
/// released. To avoid this, expando properties cannot be added to numbers.
/// The same argument applies to strings, booleans and `null`, which also have
/// literals that evaluate to identical values when they occur more than once.
///
/// There is no restriction on other classes, even for compile time constant
/// objects. Be careful if adding expando properties to compile time constants,
/// since they will stay alive forever.
class Expando<T extends Object> {
/// The name of the this [Expando] as passed to the constructor. If
/// no name was passed to the constructor, the name is `null`.
final String? name;
/// Creates a new [Expando]. The optional name is only used for
/// debugging purposes and creating two different [Expando]s with the
/// same name yields two [Expando]s that work on different properties
/// of the objects they are used on.
external Expando([String? name]);
/// Expando toString method override.
String toString() => "Expando:$name";
/// Gets the value of this [Expando]'s property on the given
/// object. If the object hasn't been expanded, the method returns
/// `null`.
///
/// The object must not be a number, a string, a boolean, `null`, a
/// `dart:ffi` pointer, a `dart:ffi` struct, or a `dart:ffi` union.
external T? operator [](Object object);
/// Sets the value of this [Expando]'s property on the given
/// object. Properties can effectively be removed again by setting
/// their value to `null`.
///
/// The object must not be a number, a string, a boolean, `null`, a
/// `dart:ffi` pointer, a `dart:ffi` struct, or a `dart:ffi` union.
external void operator []=(Object object, T? value);
}