C# Conversion of lambda expression

Question

What is the way to convert the following into lambda expression?

ThreadPool.QueueUserWorkItem(delegate
     {
        Console.WriteLine("Current Thread Id is {0}:",
         Thread.CurrentThread.ManagedThreadId);
        Console.WriteLine("I will be used as Callback");
      }
    );

Andrew Hare · Accepted Answer · 2009-11-25 05:58:20Z

5

You could definitely write this as a lambda expression:

// The underscore is simply a placeholder for the "state"
// parameter that the WaitCallback delegate expects - you could
// use any character but you must specify one as lamba expressions cannot
// omit parameters like anonymous functions can.
ThreadPool.QueueUserWorkItem((_) =>
    {
        Console.WriteLine("Current Thread Id is {0}:",
        Thread.CurrentThread.ManagedThreadId);
        Console.WriteLine("I will be used as Callback");
    });

But remember that a lambda expression has no meaning outside of your source code. The C# compiler will convert your lambda expression right back to the code you have now.

A lambda expression is simply syntactic sugar that you can use to express an anonymous function - the compiler will convert this to either an anonymous function or an expression tree.

edited Nov 25, 2009 at 5:58

answered Nov 25, 2009 at 5:52

Andrew Hare

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4 Comments

user215675 Over a year ago

Andrew ,what is the use of "_" (underscore) ?

Andrew Hare Over a year ago

Sorry, yes it's in the comment. Basically you need to throw something in there to be a placeholder.

porges Over a year ago

The (_) => ... parameter would be more self-explanatory as state => ....

Charlie Flowers Over a year ago

FYI, you don't need those parentheses around the underscore. You can just do: ThreadPool.QueueUserWorkItem( _ => { /* block omitted */ });

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