Extract ImmutableSharedKeysMap class from TransitiveInfoProviderMap.
PiperOrigin-RevId: 159498323
diff --git a/src/main/java/com/google/devtools/build/lib/collect/CompactImmutableMap.java b/src/main/java/com/google/devtools/build/lib/collect/CompactImmutableMap.java
new file mode 100644
index 0000000..d410d0c
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/collect/CompactImmutableMap.java
@@ -0,0 +1,59 @@
+// 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.
+ *
+ * <p>TODO: Convert to interface once we move to Java 8.
+ */
+public abstract class CompactImmutableMap<K, V> implements Iterable<K> {
+
+ public boolean containsKey(K key) {
+ return get(key) != null;
+ }
+
+ public abstract V get(K key);
+
+ public abstract int size();
+
+ public abstract K keyAt(int index);
+
+ public abstract V valueAt(int index);
+
+ @Override
+ public Iterator<K> iterator() {
+ return new ImmutableMapSharedKeysIterator();
+ }
+
+ private class ImmutableMapSharedKeysIterator implements Iterator<K> {
+ int index = 0;
+
+ @Override
+ public boolean hasNext() {
+ return index < size();
+ }
+
+ @Override
+ public K next() {
+ K key = keyAt(index);
+ ++index;
+ return key;
+ }
+ }
+}
