copybara-service · Jul 12, 2025
diff --git a/hilt-android/main/java/dagger/hilt/android/lifecycle/HiltViewModelExtras.kt b/hilt-android/main/java/dagger/hilt/android/lifecycle/HiltViewModelExtras.kt
@@ -0,0 +1,142 @@
+/*
+ * Copyright (C) 2025 The Dagger Authors.
+ *
+ * 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.
+ */
+
+package dagger.hilt.android.lifecycle
+
+import androidx.lifecycle.viewmodel.CreationExtras
+import dagger.hilt.android.lifecycle.HiltViewModelExtras.Key
+import kotlin.jvm.JvmOverloads
+import kotlin.jvm.JvmStatic
+
+/**
+ * A map-like object holding pairs of [HiltViewModelExtras.Key] and [Any], enabling efficient value
+ * retrieval for each key. Each key in [HiltViewModelExtras] is unique, storing only one value per
+ * key.
+ *
+ * [HiltViewModelExtras] are bound in the [dagger.hilt.android.components.ViewModelComponent] if set
+ * in the view model's [CreationExtras] with [HiltViewModelExtras.CreationExtrasKey].
+ *
+ * This abstract class supports read-only access; use [MutableHiltViewModelExtras] for read-write
+ * access.
+ */
+abstract class HiltViewModelExtras internal constructor() {
+  internal val extras: MutableMap<Key<*>, Any?> = mutableMapOf()
+
+  /**
+   * Key for the elements of [HiltViewModelExtras]. [T] represents the type of element associated
+   * with this key.
+   */
+  interface Key<T>
+
+  /**
+   * Returns the value to which the specified [key] is associated, or null if this
+   * [HiltViewModelExtras] contains no mapping for the key.
+   */
+  abstract operator fun <T> get(key: Key<T>): T?
+
+  /** Compares the specified object with this [HiltViewModelExtras] for equality. */
+  override fun equals(other: Any?): Boolean = other is HiltViewModelExtras && extras == other.extras
+
+  /** Returns the hash code value for this [HiltViewModelExtras]. */
+  override fun hashCode(): Int = extras.hashCode()
+
+  /**
+   * Returns a string representation of this [HiltViewModelExtras]. The string representation
+   * consists of a list of key-value mappings in the order returned by the [HiltViewModelExtras]'s
+   * iterator.
+   */
+  override fun toString(): String = "HiltViewModelExtras(extras=$extras)"
+
+  /** An empty read-only [HiltViewModelExtras]. */
+  object Empty : HiltViewModelExtras() {
+    override fun <T> get(key: Key<T>): T? = null
+  }
+
+  companion object {
+    /** The [CreationExtras.Key] used to store a [HiltViewModelExtras] in [CreationExtras]. */
+    @JvmField val HILT_VIEW_MODEL_EXTRAS_KEY = CreationExtras.Key<HiltViewModelExtras>()
+
+    /** Returns a unique [Key] to be associated with an extra. */
+    @JvmStatic inline fun <reified T> Key(): Key<T> = object : Key<T> {}
+  }
+}
+
+/**
+ * A modifiable [HiltViewModelExtras] that holds pairs of [HiltViewModelExtras.Key] and [Any],
+ * allowing efficient value retrieval for each key.
+ *
+ * Each key in [HiltViewModelExtras] is unique, storing only one value per key.
+ *
+ * @see [HiltViewModelExtras]
+ */
+class MutableHiltViewModelExtras
+/**
+ * Constructs a [MutableHiltViewModelExtras] containing the elements of the specified
+ * [initialExtras], in the order they are returned by the [Map]'s iterator.
+ */
+internal constructor(initialExtras: Map<Key<*>, Any?>) : HiltViewModelExtras() {
+
+  /**
+   * Constructs a [MutableHiltViewModelExtras] containing the elements of the specified
+   * [initialExtras], in the order they are returned by the [HiltViewModelExtras]'s iterator.
+   */
+  @JvmOverloads constructor(initialExtras: HiltViewModelExtras = Empty) : this(initialExtras.extras)
+
+  init {
+    extras += initialExtras
+  }
+
+  /** Associates the specified [t] with the specified [key] in this [HiltViewModelExtras]. */
+  operator fun <T> set(key: Key<T>, t: T) {
+    extras[key] = t
+  }
+
+  /**
+   * Returns the value to which the specified [key] is associated, or null if this
+   * [HiltViewModelExtras] contains no mapping for the key.
+   */
+  @Suppress("UNCHECKED_CAST") override fun <T> get(key: Key<T>): T? = extras[key] as T?
+}
+
+/**
+ * Checks if the [HiltViewModelExtras] contains the given [key].
+ *
+ * This method allows to use the `key in hiltViewModelExtras` syntax for checking whether an [key]
+ * is contained in the [HiltViewModelExtras].
+ */
+operator fun HiltViewModelExtras.contains(key: Key<*>): Boolean = key in extras
+
+/**
+ * Creates a new read-only [HiltViewModelExtras] by replacing or adding entries to [this] extras
+ * from another [hiltViewModelExtras].
+ *
+ * The returned [HiltViewModelExtras] preserves the entry iteration order of the original
+ * [HiltViewModelExtras].
+ *
+ * Those entries of another [hiltViewModelExtras] that are missing in [this] extras are iterated in
+ * the end in the order of that [hiltViewModelExtras].
+ */
+operator fun HiltViewModelExtras.plus(
+  hiltViewModelExtras: HiltViewModelExtras
+): MutableHiltViewModelExtras =
+  MutableHiltViewModelExtras(initialExtras = extras + hiltViewModelExtras.extras)
+
+/**
+ * Appends or replaces all entries from the given [hiltViewModelExtras] in [this] mutable extras.
+ */
+operator fun MutableHiltViewModelExtras.plusAssign(hiltViewModelExtras: HiltViewModelExtras) {
+  extras += hiltViewModelExtras.extras
+}