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A library for type-safe, tractable lazy evaluation and late binding in Java.

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package com.thejohnfreeman.attribute;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import com.thejohnfreeman.lazy.LateBound;
import com.thejohnfreeman.lazy.Lazy;

/**
 * An attribute that may be "read" (in the sense that its lazy wrapper is
 * stored) before it is written.
 *
 * @author thejohnfreeman
 */
public class LateBoundAttribute
    implements Attribute
{
    private final Map> _attrs = new ConcurrentHashMap<>();

    private Lazy getOrCreate(final N node) {
        return _attrs.computeIfAbsent(node, k -> LateBound.of());
    }

    /**
     * {@inheritDoc}
     *
     * 
     * May be called before the node's value has been
     * {@link #put(Object, Lazy)}.
     */
    @Override
    public Lazy get(final N node) {
        return getOrCreate(node);
    }

    @Override
    public void put(final N node, final Lazy value)
        throws IllegalStateException
    {
        final Lazy existing = _attrs.get(node);
        if (existing != null) {
            if (existing instanceof LateBound) {
                ((LateBound)existing).bind(value);
            } else {
                throw new IllegalStateException(String.format(
                    "attribute already assigned:%n  key: %s%n  value: %s",
                    node, value));
            }
        }
        _attrs.put(node, value);
    }
}