C# Func: access local variables in a block

Question

Say I have this block of code in C#:

static void Main(string[] args)
{
    List<Func<int>> fs = new List<Func<int>>();

    for (int i = 0; i < 5; i++)
        fs.Add(() => { return i; });

    for (int i = 0; i < 5; i++)
        Console.WriteLine(fs[i]());

    Console.ReadLine();
}

When I run it, I expected it to print

but it prints

instead. My understanding is that the code in Func only keeps an address to i instead of getting the value of i, and this approach should be avoided.

So my question is that, is there a way to capture the local variables and pass them into Func by value?

I have not found it yet, but I know there are duplicates of this. See also [Closing over the loop variable considered harmful](http://blogs.msdn.com/b/ericlippert/archive/2009/11/12/closing-over-the-loop-variable-considered-harmful.aspx) — crashmstr, Jul 31 '14 at 14:13

score 4 · Accepted Answer · answered Jul 31 '14 at 14:10

You can use the scope in the for loop to capture a copy of the value of i:

static void Main(string[] args)
{
    List<Func<int>> fs = new List<Func<int>>();

    for (int i = 0; i < 5; i++)
    {
        var copyOfi = i;
        fs.Add(() => { return copyOfi; });
    }

    for (int i = 0; i < 5; i++)
        Console.WriteLine(fs[i]());

    Console.ReadLine();
}

score 1 · Answer 2 · answered Jul 31 '14 at 14:10

1

Just store the loop variable in a local variable inside the loop and use it in the lambda expression.

answered Jul 31 '14 at 14:10

Thierry

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C# Func: access local variables in a block

2 Answers2