1 files changed, 58 insertions, 0 deletions
diff --git a/src/main/java/com/google/escapevelocity/ImmutableSet.java b/src/main/java/com/google/escapevelocity/ImmutableSet.java
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+++ b/src/main/java/com/google/escapevelocity/ImmutableSet.java
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+/*
+ * Copyright (C) 2017 Google, Inc.
+ *
+ * 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.escapevelocity;
+
+import java.util.AbstractSet;
+import java.util.Arrays;
+import java.util.Iterator;
+
+/**
+ * An immutable set. This implementation is only suitable for sets with a small number of elements.
+ *
+ * @author emcmanus@google.com (Éamonn McManus)
+ */
+class ImmutableSet<E> extends AbstractSet<E> {
+  private final E[] elements;
+
+  private ImmutableSet(E[] elements) {
+    this.elements = elements;
+  }
+
+  @Override
+  public Iterator<E> iterator() {
+    return Arrays.asList(elements).iterator();
+  }
+
+  @Override
+  public int size() {
+    return elements.length;
+  }
+
+  @SafeVarargs
+  static <E> ImmutableSet<E> of(E... elements) {
+    int len = elements.length;
+    for (int i = 0; i < len - 1; i++) {
+      for (int j = len - 1; j > i; j--) {
+        if (elements[i].equals(elements[j])) {
+          // We want to exclude elements[j] from the final set. We can do that by copying the
+          // current last element in place of j (this might be j itself) and then reducing the
+          // size of the set.
+          elements[j] = elements[len - 1];
+          len--;
+        }
+      }
+    }
+    return new ImmutableSet<>(Arrays.copyOf(elements, len));
+  }
+}