godot-host-test/addons/GodotDI/EnumerableExtensions.cs

using System.Collections.Generic;

namespace GodotHostTest.GodotDI;

public static class EnumerableExtensions
{
    public enum SingleFailureReason
    {
        LessThanOne,
        MoreThanOne
    }

    public static T? Single<T>(this IEnumerable<T> enumerable, out SingleFailureReason? failureReason)
        where T : class
    {
        using var enumerator = enumerable.GetEnumerator();
        if (!enumerator.MoveNext())
        {
            failureReason = SingleFailureReason.LessThanOne;
            return null;
        }

        var value = enumerator.Current;
        if (enumerator.MoveNext())
        {
            failureReason = SingleFailureReason.MoreThanOne;
            return null;
        }

        failureReason = null;
        return value;
    }
}