/*
 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package org.graalvm.compiler.phases.common;

import java.util.function.Supplier;

/**
 * A {@link Supplier} which always returns the same value, computed from an other supplier on the
 * first access.
 *
 * <p>
 * This implementation is not thread-safe and assumes the underlying supplier does not return null.
 * If the underlying supplier returns null it will be called on each access until it returns a
 * non-null value.
 * </p>
 */
public class LazyValue<T> implements Supplier<T> {
    private final Supplier<T> supplier;
    private T value;

    public LazyValue(Supplier<T> supplier) {
        this.supplier = supplier;
    }

    @Override
    public T get() {
        if (value == null) {
            value = supplier.get();
        }
        return value;
    }
}