Scope of variables inside anonymous functions in C#

Question

I have a doubt in scope of varibles inside anonymous functions in C#.

Consider the program below:

 delegate void OtherDel(int x);

        public static void Main()
        {
            OtherDel del2;
            {
                int y = 4;
                del2 = delegate
                {
                      Console.WriteLine("{0}", y);//Is y out of scope
                };
            }

           del2();
        }

My VS2008 IDE gives the following errors: [Practice is a class inside namespace Practice]

1.error CS1643: Not all code paths return a value in anonymous method of type 'Practice.Practice.OtherDel' 2.error CS1593: Delegate 'OtherDel' does not take '0' arguments.

It is told in a book: Illustrated C# 2008(Page 373) that the int variable y is inside the scope of del2 definition. Then why these errors.

Marc Gravell · Accepted Answer · 2010-05-23 07:44:21Z

4

Two problem;

you aren't passing anything into your del2() invoke, but it (OtherDel) takes an integer that you don't use - you still need to supply it, though (anonymous methods silently let you not declare the params if you don't use them - they still exist, though - your method is essentially the same as del2 = delegate(int notUsed) {...})
the delegate (OtherDel) must return an int - your method doesn't

The scoping is fine.

answered May 23, 2010 at 7:44

Marc Gravell

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2 Comments

Richard Over a year ago

#1 is completely correct, but #2: check out OtherDel's type declaration at the top of the OP's code: delegate void OtherDel(int x) -- it doesn't return anything. [EDIT: this was changed in an edit to the question]

Marc Gravell Over a year ago

The answer reflects the question at the time I posted this ;p

Darin Dimitrov · Accepted Answer · 2010-05-23 07:44:20Z

2

The error has nothing to do with scopes. Your delegate must return an integer value and take an integer value as parameter:

del2 = someInt =>
{
    Console.WriteLine("{0}", y);
    return 17;
};
int result = del2(5);

So your code might look like this:

delegate int OtherDel(int x);
public static void Main()
{
    int y = 4;
    OtherDel del = x =>
    {
        Console.WriteLine("{0}", x);
        return x;
    };
    int result = del(y);
}

answered May 23, 2010 at 7:44

Darin Dimitrov

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