What was the design decision for variadic functions needing an array?

Question

I am curious and hopefully someone can shed somelight on this - but why do the C# functions that take 'params' have to be an array?

I get that the objects in the parameters list are entered into an array but what if someone wants to create a variadic function that takes in an undefined number of array objects?

Take this function for example...

private Int32 Sum(params Int32[] numbers)
{
    return numbers.Sum(); // Using LINQ here to sum
}

Pretty straight forward, it can take in a different amount of numbers - for example...

Int32 x = Sum(1);
Int32 y = Sum(1, 2);
Int32 z = Sum(1, 2, 3);

Now lets say I want to create a function that takes in a different amount of Integer arrays and sums up all the numbers. As far as I am aware I would have to consider boxing...

private Int32 SumArrays(params Object[] numbers)
{
    Int32 total = 0;
    foreach (Object o in numbers)
    {
        Int32[] array = (Int32[])o;

        total += array.Sum();
    }
    return total;
}

Which could then be used like...

Int32[] arr1 = new Int32[] { 1, 2, 3 };
Int32[] arr2 = new Int32[] { 1, 2, 3, 4 };
Int32[] arr3 = new Int32[] { 1, 2, 3, 4, 5 };

Int32 x = SumArrays((Object)arr1, (Object)arr2);
Int32 y = SumArrays((Object)arr1, (Object)arr2, (Object)arr3);

What was the reasoning behind this? Why wasn't this ever implemented as just a single non array variable? Such as params Int32?

Answer 1

The functionality is already there, no need to resort to boxing:

private int SumAll(params int[][] args)
{
    int result = 0;
    for (int x = 0; x < args.Length; x++)
    {
        for (int y = 0; y < args[x].Length; y++)
        {
            result += args[x][y];
        }
    }
    return result;
}

You just need to add it an array of arrays.

Answer 2

The params get rolled into a single object, and the lowest-level object that can hold a collection is an array. If you want a function that takes a variable number of arrays of ints, then it should be declared as taking an array of int arrays.

static int SumArrays(params int[][] data)
{
    int rval = 0;
    for (int i = 0; i < data.Length; i++)
    {
        rval += data[i].Sum();
    }
    return rval;
}