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 shape-functional-java Show documentation

Functional programming library

There is a newer version: 3.1.0

Show newest version

/*
 * 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