1 /* 2 * Copyright (C) 2023 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 com.android.cobalt.collect; 18 19 import com.google.common.collect.ImmutableList; 20 import com.google.common.collect.ImmutableListMultimap; 21 import com.google.common.collect.ImmutableMap; 22 23 import java.util.function.Function; 24 import java.util.stream.Collector; 25 26 /** Helper functions for working with immutable collections. */ 27 public final class ImmutableHelpers { ImmutableHelpers()28 private ImmutableHelpers() {} 29 30 /** Collector to create immutable lists. */ toImmutableList()31 public static <T> Collector<T, ?, ImmutableList<T>> toImmutableList() { 32 return Collector.of( 33 ImmutableList.Builder<T>::new, 34 (l, v) -> l.add(v), 35 (l1, l2) -> l1.addAll(l2.build()), 36 ImmutableList.Builder::build); 37 } 38 39 /** Collector to create immutable maps. */ toImmutableMap( Function<? super T, ? extends K> keyMap, Function<? super T, ? extends V> valueMap)40 public static <T, K, V> Collector<T, ?, ImmutableMap<K, V>> toImmutableMap( 41 Function<? super T, ? extends K> keyMap, Function<? super T, ? extends V> valueMap) { 42 return Collector.of( 43 ImmutableMap.Builder<K, V>::new, 44 (m, e) -> m.put(keyMap.apply(e), valueMap.apply(e)), 45 (m1, m2) -> m1.putAll(m2.build()), 46 ImmutableMap.Builder::build); 47 } 48 49 /** Collector to create immutable list multimaps. */ toImmutableListMultimap( Function<? super T, ? extends K> keyMap, Function<? super T, ? extends V> valueMap)50 public static <T, K, V> Collector<T, ?, ImmutableListMultimap<K, V>> toImmutableListMultimap( 51 Function<? super T, ? extends K> keyMap, Function<? super T, ? extends V> valueMap) { 52 return Collector.of( 53 ImmutableListMultimap.Builder<K, V>::new, 54 (m, e) -> m.put(keyMap.apply(e), valueMap.apply(e)), 55 (m1, m2) -> m1.putAll(m2.build()), 56 ImmutableListMultimap.Builder::build); 57 } 58 } 59