using System;

using System.Collections.Generic;

using System.Linq;

using System.Runtime.InteropServices;

​

public static class Program

{

    public static void Main()

    {

        List<int> list = new(Enumerable.Range(1, 15));

        Console.WriteLine($"Before RemoveAll: [{String.Join(", ", list)}]");

        try

        {

            list.RemoveAll((item, index) =>

            {

                if (item == 10) throw new Exception();

                bool removeIt = item % 2 == 1;

                if (removeIt) Console.WriteLine($"Removing #{item}");

                return removeIt;

            });

        }

        catch (Exception ex) { Console.WriteLine(ex); }

        finally

        {

            Console.WriteLine($"After RemoveAll: [{String.Join(", ", list)}]");

        }

    }

​

    /// <summary>

    /// Removes all the elements that match the conditions defined by the specified

    /// predicate. In case the predicate fails, the integrity of the list is preserved.

    /// </summary>

    public static int RemoveAll<T>(this List<T> list, Func<T, int, bool> predicate)

    {

        ArgumentNullException.ThrowIfNull(list);

        ArgumentNullException.ThrowIfNull(predicate);

​

        Span<T> span = CollectionsMarshal.AsSpan(list);

        int i = 0, j = 0;

        try

        {

            for (; i < span.Length; i++)

            {

                if (predicate(span[i], i)) continue;

                if (j < i) span[j] = span[i];

                j++;

            }

        }

        finally

        {

            if (j < i)

            {

                for (; i < span.Length; i++, j++)

                    span[j] = span[i];

                list.RemoveRange(j, span.Length - j);

            }

        }

        return i - j;

    }

}