EnumerableHelpers.cs

Go to the documentation of this file.

namespace System.Collections.Generic;
 
internal static class EnumerableHelpers
{
    internal static T[] ToArray<T>(IEnumerable<T> source, out int length)
    {
        if (source is ICollection<T> { Count: var count } collection)
        {
            if (count != 0)
            {
                T[] array = new T[count];
                collection.CopyTo(array, 0);
                length = count;
                return array;
            }
        }
        else
        {
            using IEnumerator<T> enumerator = source.GetEnumerator();
            if (enumerator.MoveNext())
            {
                T[] array2 = new T[4]
                {
                    enumerator.Current,
                    default(T),
                    default(T),
                    default(T)
                };
                int num = 1;
                while (enumerator.MoveNext())
                {
                    if (num == array2.Length)
                    {
                        int num2 = num << 1;
                        if ((uint)num2 > Array.MaxLength)
                        {
                            num2 = ((Array.MaxLength <= num) ? (num + 1) : Array.MaxLength);
                        }
                        Array.Resize(ref array2, num2);
                    }
                    array2[num++] = enumerator.Current;
                }
                length = num;
                return array2;
            }
        }
        length = 0;
        return Array.Empty<T>();
    }
 
    internal static void Copy<T>(IEnumerable<T> source, T[] array, int arrayIndex, int count)
    {
        if (source is ICollection<T> collection)
        {
            collection.CopyTo(array, arrayIndex);
        }
        else
        {
            IterativeCopy(source, array, arrayIndex, count);
        }
    }
 
    internal static void IterativeCopy<T>(IEnumerable<T> source, T[] array, int arrayIndex, int count)
    {
        int num = arrayIndex + count;
        foreach (T item in source)
        {
            array[arrayIndex++] = item;
        }
    }
 
    internal static T[] ToArray<T>(IEnumerable<T> source)
    {
        if (source is ICollection<T> { Count: var count } collection)
        {
            if (count == 0)
            {
                return Array.Empty<T>();
            }
            T[] array = new T[count];
            collection.CopyTo(array, 0);
            return array;
        }
        LargeArrayBuilder<T> largeArrayBuilder = new LargeArrayBuilder<T>(initialize: true);
        largeArrayBuilder.AddRange(source);
        return largeArrayBuilder.ToArray();
    }
}