com.shapesecurity.functional.Thunk Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of shift Show documentation

Shift format ECMAScript 6 AST tooling

There is a newer version: 2.2.0

/*
 * Copyright 2014 Shape Security, 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.shapesecurity.functional;

import java.util.function.Supplier;

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

// Used for lazy evaluation.
// @FunctionalInterface
public final class Thunk {
  @NotNull
  private final Supplier supplier;
  // Exception on style: private nullable.
  @Nullable
  private volatile A value = null;

  private Thunk(@NotNull Supplier supplier) {
    this.supplier = supplier;
  }

  @NotNull
  public static  Thunk constant(@NotNull final A value) {
    Thunk t = new Thunk<>(() -> value);
    t.value = value;
    return t;
  }

  @NotNull
  public static  Thunk from(@NotNull Supplier supplier) {
    return new Thunk<>(supplier);
  }

  @NotNull
  public final A get() {
    // Double locked.
    if (this.value == null) {
      synchronized (this) {
        if (this.value == null) {
          A v = supplier.get();
          this.value = v;
          return v;
        } else {
          return this.value;
        }
      }
    } else {
      return this.value;
    }
  }
}

Related Artifacts