IIListProvider.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Generic;

namespace System.Linq
{
    /// <summary>
    /// An iterator that can produce an array or <see cref="List{TElement}"/> through an optimized path.
    /// </summary>
    internal interface IIListProvider<TElement> : IEnumerable<TElement>
    {
        /// <summary>
        /// Produce an array of the sequence through an optimized path.
        /// </summary>
        /// <returns>The array.</returns>
        TElement[] ToArray();

        /// <summary>
        /// Produce a <see cref="List{TElement}"/> of the sequence through an optimized path.
        /// </summary>
        /// <returns>The <see cref="List{TElement}"/>.</returns>
        List<TElement> ToList();

        /// <summary>
        /// Returns the count of elements in the sequence.
        /// </summary>
        /// <param name="onlyIfCheap">If true then the count should only be calculated if doing
        /// so is quick (sure or likely to be constant time), otherwise -1 should be returned.</param>
        /// <returns>The number of elements.</returns>
        int GetCount(bool onlyIfCheap);
    }
}