1 /* 2 * Copyright 2019 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package androidx.compose.runtime 18 19 /** 20 * [StableMarker] marks an annotation as indicating a type is stable. A stable type obeys the 21 * following assumptions, 22 * 1) The result of [equals] will always return the same result for the same two instances. 23 * 2) When a public property of the type changes, composition will be notified. 24 * 3) All public property types are stable. 25 * 26 * A type that is immutable obeys the above assumptions because the public values will never change. 27 * The [Immutable] annotation is provided to mark immutable types as stable. 28 * 29 * An object whose public properties do not change but is not immutable (for example, it has private 30 * mutable state or uses property delegation to a [androidx.compose.runtime.MutableState] object, 31 * but is otherwise immutable), should use the [Stable] annotation. 32 * 33 * Mutable object that do not notify composition when they changed should not be marked as stable. 34 * 35 * When all types passed as parameters to a [androidx.compose.runtime.Composable] function are 36 * marked as stable then the parameter values are compared for equality based on positional 37 * memoization and the call is skipped if all the values are the equal to the previous call. 38 * 39 * Primitive value types (such as Int, Float, etc), String and enum types are considered, a priori, 40 * stable. 41 * 42 * @see Immutable 43 * @see Stable 44 */ 45 @MustBeDocumented 46 @Target(AnnotationTarget.ANNOTATION_CLASS, AnnotationTarget.CLASS) 47 @Retention(AnnotationRetention.BINARY) 48 public annotation class StableMarker 49