src/main/java/com/google/devtools/build/lib/skyframe/MutableSupplier.java

// Copyright 2014 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.skyframe;

import com.google.common.base.MoreObjects;
import com.google.common.base.Supplier;

/**
 * Supplier whose value can be changed by clients who have a reference to it as a MutableSupplier.
 * Unlike an {@code AtomicReference}, clients who are passed a MutableSupplier as a Supplier cannot
 * change its value without a reckless cast.
 */
public class MutableSupplier<T> implements Supplier<T> {
  private T val;

  @Override
  public T get() {
    return val;
  }

  /**
   * Sets the value of the object supplied. Do not cast a Supplier to a MutableSupplier in order to
   * call this method!
   */
  public void set(T newVal) {
    val = newVal;
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(getClass())
        .add("val", val).toString();
  }
}