hazelcast-master/hazelcast/src/main/java/com/hazelcast/jet/impl/util/MemoizingSupplier.java
/*
 * Copyright (c) 2008-2023, Hazelcast, Inc. 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.hazelcast.jet.impl.util;

import java.util.function.Supplier;

/**
 * Wraps a {@code Supplier} and returns a memoizing supplier which calls
 * it only on the first invocation of {@code get()}, and afterwards
 * returns the remembered instance.
 */
final class MemoizingSupplier<T> implements Supplier<T> {
    private Supplier<T> onceSupplier;
    private T remembered;

    MemoizingSupplier(Supplier<T> onceSupplier) {
        this.onceSupplier = onceSupplier;
    }

    @Override
    public T get() {
        if (onceSupplier == null) {
            return remembered;
        }
        remembered = onceSupplier.get();
        onceSupplier = null;
        return remembered;
    }
}
