c# using Array.ForEach Action Predicate with array of value type or string

Question

Am I correct in thinking the following snippet does not work (the array items are not modified) because the array is of integer which is value type.

class Program
{
    public static void Main()
    {
        int[] ints = new int[] { 1,2 };

        Array.ForEach(ints, new Action<int>(AddTen));

        // ints is not modified
    }
    static void AddTen(int i)
    {
        i+=10;
    }
}

The same would apply if the example used an array of string, presumably because string is immutable.

The question I have is:-

Is there a way around this? I can't change the signature of the callback method - for instance by adding the ref keyword and I don't want to wrap the value type with a class - which would work...

(Of course, I could simply write an old fashioned foreach loop to do this!)

Answer 1

You are simply changing the local variable - not the item in the list. To do this, you want ConvertAll, which creates a new list/array:

    int[] ints = new int[] { 1,2 };

    int[] newArr = Array.ConvertAll<int,int>(ints, AddTen);

with:

static int AddTen(int i)
{
    return i+10;
}

This can also be written with an anonymous method:

int[] newArr = Array.ConvertAll<int,int>(ints,
    delegate (int i) { return i+ 10;});

Or in C# 3.0 as a lambda:

int[] newArr = Array.ConvertAll(ints, i=>i+10);

Other than that... a for loop:

for(int i = 0 ; i < arr.Length ; i++) {
    arr[i] = AddTen(arr[i]); // or more directly...
}

But one way or another, you are going to have to get a value out of your method. Unless you change the signature, you can't.