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Reactive Extensions for Java
There is a newer version: 3.1.9
/*
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * 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 io.reactivex.rxjava3.internal.operators.single;

import java.util.*;

import org.reactivestreams.Publisher;

import io.reactivex.rxjava3.core.*;
import io.reactivex.rxjava3.functions.*;

/**
 * Helper utility class to support Single with inner classes.
 */
public final class SingleInternalHelper {

    /** Utility class. */
    private SingleInternalHelper() {
        throw new IllegalStateException("No instances!");
    }

    enum NoSuchElementSupplier implements Supplier {
        INSTANCE;

        @Override
        public NoSuchElementException get() {
            return new NoSuchElementException();
        }
    }

    public static Supplier emptyThrower() {
        return NoSuchElementSupplier.INSTANCE;
    }

    @SuppressWarnings("rawtypes")
    enum ToFlowable implements Function {
        INSTANCE;
        @SuppressWarnings("unchecked")
        @Override
        public Publisher apply(SingleSource v) {
            return new SingleToFlowable(v);
        }
    }

    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static  Function, Publisher> toFlowable() {
        return (Function)ToFlowable.INSTANCE;
    }

    static final class ToFlowableIterator implements Iterator> {
        private final Iterator> sit;

        ToFlowableIterator(Iterator> sit) {
            this.sit = sit;
        }

        @Override
        public boolean hasNext() {
            return sit.hasNext();
        }

        @Override
        public Flowable next() {
            return new SingleToFlowable<>(sit.next());
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    static final class ToFlowableIterable implements Iterable> {

        private final Iterable> sources;

        ToFlowableIterable(Iterable> sources) {
            this.sources = sources;
        }

        @Override
        public Iterator> iterator() {
            return new ToFlowableIterator<>(sources.iterator());
        }
    }

    public static  Iterable> iterableToFlowable(final Iterable> sources) {
        return new ToFlowableIterable<>(sources);
    }
}