src/main/java/com/google/devtools/build/lib/collect/CompactImmutableMap.java

// Copyright 2017 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.collect;

import java.util.Iterator;

/**
 * A minimal map interface that avoids methods whose implementation tends to force GC churn, or
 * otherwise overly constrain implementation freedom.
 */
public interface CompactImmutableMap<K, V> extends Iterable<K> {

  default boolean containsKey(K key) {
    return get(key) != null;
  }

  V get(K key);

  int size();

  K keyAt(int index);

  V valueAt(int index);

  @Override
  default Iterator<K> iterator() {
    return new Iterator<K>() {
      int index = 0;

      @Override
      public boolean hasNext() {
        return index < size();
      }

      @Override
      public K next() {
        K key = keyAt(index);
        ++index;
        return key;
      }
    };
  }
}