*
     * @param key the key for which to retrieve the session data, must not be {@code null}
     * @param supplier the supplier will compute the new value
     * @return the session data associated with the key
     */
    @Nullable
    <T> T computeIfAbsent(@Nonnull Key<T> key, @Nonnull Supplier<T> supplier);

    /**
     * Create a key using the given class as an identifier and as the type of the object.
     */

        public int hashCode() {
            return hash;
        }
    }

    static class CachingSupplier<T> implements Supplier<T> {
        final Supplier<T> supplier;
        volatile Object value;

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

        @Override
        @SuppressWarnings({"unchecked", "checkstyle:InnerAssignment"})
        public T get() {

import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Supplier;
import java.util.stream.Collectors;

import com.google.inject.AbstractModule;
import com.google.inject.binder.AnnotatedBindingBuilder;
import com.google.inject.name.Names;

        Supplier<T> s = asSupplier(supplier);
        if (cache == null) {
            return s.get();
        } else {
            return cache.computeIfAbsent(groupId, artifactId, version, tag, s);
        }
    }

    private static <T> T cache(ModelCache cache, Source source, String tag, Callable<T> supplier) {
        Supplier<T> s = asSupplier(supplier);

 * model builder.
 *
 */
public interface ModelCache {

    <T> T computeIfAbsent(String groupId, String artifactId, String version, String tag, Supplier<T> data);

    <T> T computeIfAbsent(Source path, String tag, Supplier<T> data);

                }
            }
            return model;
        }

        public Model computeIfAbsent(Supplier<Model> supplier) {
            if (!set) {
                synchronized (this) {
                    if (!set) {
                        this.set = true;
                        this.model = supplier.get();
                        this.notifyAll();
                    }
                }
            }

import org.eclipse.aether.util.repository.SimpleArtifactDescriptorPolicy;

import static java.util.Objects.requireNonNull;

/**
 * A simple {@link Supplier} of {@link SessionBuilder} instances, that on each call supplies newly
 * constructed instance. To create session out of builder, use {@link SessionBuilder#build()}. For proper closing
 * of sessions, use {@link CloseableSession#close()} method on built instance(s).

import java.nio.file.Path;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;

import org.apache.maven.artifact.DefaultArtifact;
import org.apache.maven.internal.transformation.TransformationFailedException;
import org.apache.maven.model.building.ModelBuildingException;

    @Override
    public void debug(Throwable error) {
        logger.debug("", error);
    }

    @Override
    public void debug(Supplier<String> content) {
        if (isDebugEnabled()) {
            logger.debug(content.get());
        }
    }

    @Override
    public void debug(Supplier<String> content, Throwable error) {
        if (isDebugEnabled()) {
            logger.debug(content.get(), error);
        }
    }

        throw (T) t; // rely on vacuous cast
    }

    static class LazyMap<K, V> extends AbstractMap<K, V> {
        private final Supplier<Map<K, V>> supplier;
        private volatile Map<K, V> delegate;

        LazyMap(Supplier<Map<K, V>> supplier) {
            this.supplier = supplier;
        }

        @Override
        public Set<Entry<K, V>> entrySet() {
            if (delegate == null) {