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Multiplatform implementations of the stable and immutable annotations

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package androidx.compose.runtime

/*
 * Copyright 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * This is a backport annotation of Stable from the androidx.compose.runtime:runtime artifact.
 *
 * Stable is used to communicate some guarantees to the compose compiler about how a certain type
 * or function will behave.
 *
 * When applied to a class or an interface, [Stable] indicates that the following must be true:
 *
 *   1) The result of [equals] will always return the same result for the same two instances.
 *   2) When a public property of the type changes, composition will be notified.
 *   3) All public property types are stable.
 *
 * When applied to a function or a property, the [Stable] annotation indicates that the function
 * will return the same result if the same parameters are passed in. This is only meaningful if
 * the parameters and results are themselves [Stable], [Immutable], or primitive.
 *
 * The invariants that this annotation implies are used for optimizations by the compose compiler,
 * and have undefined behavior if the above assumptions are not met. As a result, one should not
 * use this annotation unless they are certain that these conditions are satisfied.
 *
 * @see Immutable
 * @see StableMarker
 */
@MustBeDocumented
@Target(
  AnnotationTarget.CLASS,
  AnnotationTarget.FUNCTION,
  AnnotationTarget.PROPERTY_GETTER,
  AnnotationTarget.PROPERTY,
)
@Retention(AnnotationRetention.BINARY)
@StableMarker
public annotation class Stable