大数的 C# linq Sum() 扩展

Question

我有一个简单的 Sum 扩展:

public static int? SumOrNull<TSource>(this IEnumerable<TSource> source, Func<TSource, int> projection)
{
    return source.Any()
        ? source.Sum(projection)
        : (int?)null;
}

但它会导致 System.OverflowException: Arithmetic operation resulted in overflow.

我想做的是这样的:

public static ulong? SumOrNull<TSource>(this IEnumerable<TSource> source, Func<TSource, int> projection)
{
    return source.Any()
        ? source.Sum(projection)
        : (ulong?)null;
}

但是 Linq Sum 没有返回 ulong 和结果编译错误的重载。 有什么办法可以做到这一点？

Answer 1

您可以手动实现它。这是一个例子:

public static ulong? SumOrNull<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, int> projection)
{
    bool any = false;

    ulong sum = 0;

    foreach (var item in source)
    {
        any = true;

        //As commented by CodesInChaos,
        //we use the checked keyword to make sure that
        //we throw an exception if there are any negative numbers
        sum = sum + (ulong)checked((uint)projection(item));
    }

    if (!any)
        return null;

    return sum;
}