Range.SpeedOpt.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections.Generic;

namespace System.Linq
{
    public static partial class Enumerable
    {
        private sealed partial class RangeIterator : IPartition<int>
        {
            public override IEnumerable<TResult> Select<TResult>(Func<int, TResult> selector)
            {
                return new SelectRangeIterator<TResult>(_start, _end, selector);
            }

            public int[] ToArray()
            {
                int[] array = new int[_end - _start];
                int cur = _start;
                for (int i = 0; i != array.Length; ++i)
                {
                    array[i] = cur;
                    ++cur;
                }

                return array;
            }

            public List<int> ToList()
            {
                List<int> list = new List<int>(_end - _start);
                for (int cur = _start; cur != _end; cur++)
                {
                    list.Add(cur);
                }

                return list;
            }

            public int GetCount(bool onlyIfCheap) => unchecked(_end - _start);

            public IPartition<int> Skip(int count)
            {
                if (count >= _end - _start)
                {
                    return EmptyPartition<int>.Instance;
                }

                return new RangeIterator(_start + count, _end - _start - count);
            }

            public IPartition<int> Take(int count)
            {
                int curCount = _end - _start;
                if (count >= curCount)
                {
                    return this;
                }

                return new RangeIterator(_start, count);
            }

            public int TryGetElementAt(int index, out bool found)
            {
                if (unchecked((uint)index < (uint)(_end - _start)))
                {
                    found = true;
                    return _start + index;
                }

                found = false;
                return 0;
            }

            public int TryGetFirst(out bool found)
            {
                found = true;
                return _start;
            }

            public int TryGetLast(out bool found)
            {
                found = true;
                return _end - 1;
            }
        }
    }
}