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• Lazy.java

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org.ethelred.util.function.Lazy Maven / Gradle / Ivy

/* (C) 2024 */
package org.ethelred.util.function;

import java.util.*;
import java.util.function.*;

/**
 * NOT THREAD SAFE - intended to be used in single request scope
 *
 * @param  The type that will be created and supplied
 */
public class Lazy implements Supplier {
    private final Supplier supplier;
    private boolean got = false;
    private boolean inGet = false;
    private T value;

    private Lazy(Supplier supplier) {
        this.supplier = supplier;
    }

    public static  Lazy lazy(Supplier supplier) {
        return new Lazy<>(Objects.requireNonNull(supplier));
    }

    public static  Lazy lazy(A argument, Function initializer) {
        Objects.requireNonNull(initializer);
        return new Lazy<>(() -> initializer.apply(argument));
    }

    public static  Lazy lazy(Supplier argument, Function initializer) {
        Objects.requireNonNull(argument);
        Objects.requireNonNull(initializer);
        return new Lazy<>(() -> initializer.apply(argument.get()));
    }

    public T get() {
        if (inGet) {
            throw new IllegalStateException("Cycle in Lazy.get()");
        }
        if (!got) {
            got = true;
            inGet = true;
            value = supplier.get();
            inGet = false;
        }
        return value;
    }
}