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Representation of a value with lazy initialization in Java.
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/*
 * Copyright 2021 Santos Zatarain Vera
 *
 * 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 mx.com.inftel.javax.lazy;

import mx.com.inftel.javax.lazy.impl.UnsafeClearableLazyImpl;

import java.util.function.Supplier;

/**
 * Represents a (clearable) value with lazy initialization.
 *
 * @param  Type of value.
 */
public interface ClearableLazy extends Lazy {

    /**
     * Gets the lazily initialized value of the current ClearableLazy instance.
     * 
     * Once the value was initialized it must not change during the rest of lifetime of this ClearableLazy instance,
     * unless is cleared. After a clear, the value will be initialized again.
     * 
     *
     * @return The lazily initialized value of the current ClearableLazy instance.
     */
    T getValue();

    /**
     * Returns {@code true} if a value for this ClearableLazy instance has been already initialized, and {@code false}
     * otherwise.
     * 
     * Once this function has returned {@code true} it stays {@code true} for the rest of lifetime of this ClearableLazy
     * instance, unless is cleared. After a clear, the value will be initialized again.
     * 
     *
     * @return {@code true} if a value for this ClearableLazy instance has been already initialized, and {@code false}
     * otherwise.
     */
    boolean isInitialized();

    /**
     * Clear the value of this ClearableLazy instance. After a clear, the value will be initialized again.
     */
    void clear();

    /**
     * Create an instance of ClearableLazy.
     * 
     * The new instance is not safe for multi-thread access.
     * 
     *
     * @param initializer Supplier for initializing the value.
     * @param          Type of value.
     * @return New instance of ClearableLazy.
     */
    static  ClearableLazy clearableLazy(Supplier initializer) {
        return new UnsafeClearableLazyImpl<>(initializer);
    }
}