src/Lucene.Net/Support/QueueExtensions.cs

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;

#nullable enable

namespace Lucene.Net.Support
{
    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You 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.
     */

    /// <summary>
    /// Extensions to <see cref="Queue{T}"/>
    /// </summary>
    internal static class QueueExtensions
    {
#if !FEATURE_QUEUE_TRYDEQUEUE_TRYPEEK
        /// <summary>
        /// Removes the object at the beginning of the <see cref="Queue{T}"/>,
        /// and copies it to the <paramref name="result"/> parameter.
        /// </summary>
        /// <typeparam name="T">The type of element in the <see cref="Queue{T}"/></typeparam>
        /// <param name="queue">The <see cref="Queue{T}"/> to be checked</param>
        /// <param name="result">The removed object</param>
        /// <returns><c>true</c> if the object was successfully removed; <c>false</c> if the <see cref="Queue{T}"/> is empty.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="queue"/> is <c>null</c>.</exception>
        public static bool TryDequeue<T>(this Queue<T> queue, [MaybeNullWhen(false)] out T result)
        {
            if (queue is null)
                throw new ArgumentNullException(nameof(queue));

            if (queue.Count > 0)
            {
                result = queue.Dequeue();
                return true;
            }

            result = default;
            return false;
        }

        /// <summary>
        /// Returns a value that indicates whether there is an object at the beginning of the <see cref="Queue{T}"/>,
        /// and if one is present, copies it to the <paramref name="result"/> parameter. The object is not removed from the <see cref="Queue{T}"/>.
        /// </summary>
        /// <typeparam name="T">The type of element in the <see cref="Queue{T}"/></typeparam>
        /// <param name="queue">The <see cref="Queue{T}"/> to be checked</param>
        /// <param name="result">If present, the object at the beginning of the <see cref="Queue{T}"/>; otherwise, the default value of <typeparamref name="T"/></param>
        /// <returns><c>true</c> if there is an object at the beginning of the <see cref="Queue{T}"/>; <c>false</c> if the <see cref="Queue{T}"/> is empty.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="queue"/> is <c>null</c>.</exception>
        public static bool TryPeek<T>(this Queue<T> queue, [MaybeNullWhen(false)] out T result)
        {
            if (queue is null)
                throw new ArgumentNullException(nameof(queue));

            if (queue.Count > 0)
            {
                result = queue.Peek();
                return true;
            }

            result = default;
            return false;
        }
#endif
    }
}