How to return a type from an anonymous method/delegate

Question

i want to return a string value from an anonymous method/delegate. How can i achieve something like this: Note this will give a compile time error: Cannot convert anonymous method to type 'string' because it is not a delegate type

            StringBuilder sb = new StringBuilder("aaa");
            sb.Replace("aaa", delegate()
            {
                return "bbb";
            });

I' am also trying to create an extension method so i can write code like:

StringBuilder sb = new StringBuilder("aaa");
sb.Replace("aaa", () =>                
{
  return "bbb";
});

What would the signiture of the extension method be?

EDIT:

We have a large internal class which generates tedious xml files. We want to make the method more readable, more than anything else. So we want to go from:

StringBuilder sb = new StringBuilder(_repository.GetGenericXml1Template());
sb.Replace("$Placeholder", GetXml1Helper());

private void string GetXml1Helper()
{
   StringBuilder sb = new StringBuilder(_repository.GetGenericXml2Template());
   sb.replace("$Var1", DB.Var1);
   ....
   return  sb.ToString();
}

So rather than having dozens of helper methods doing slightly similar things we want to at least make the code more readble.

To:

StringBuilder sb = new StringBuilder(_repository.GetGenericXml1Template());
sb.Replace("$Placeholder", () =>
{
   StringBuilder sb = new StringBuilder(_repository.GetGenericXml2Template());
   sb.replace("$Var1", DB.Var1);
   ....
   return  sb.ToString();
}
);

Answer 1

This is the correct syntax to return a string form an anonymous method. Your problem is different - you're trying to pass an anonymous method to StringBuilder.Replace() as the second argument, where it expects a string.

Why are you doing this anyway?

Answer 2

Note this will give a compile time error: Cannot convert anonymous method to type 'string' because it is not a delegate type

Your delegate is fine – the error just says that it cannot be used here because Replace expects a string as the second argument.

What would the signiture of the extension method be?

Well, something like this:

static void Replace(this StringBuilder sb, Func<string> f);

– but why would you want this? What use-case does it fulfill?

Answer 3

I believe that you need to extend the existing method.

Kindly refer to this link --> http://msdn.microsoft.com/en-us/library/bb383977.aspx

Answer 4

You could do the following:

StringBuilder sb = new StringBuilder();
Func<string> func = delegate()
{
    return "HELLO";
};
sb.Replace("", func());

Although I don't see the use of this...

Answer 5

Instead of a StringBuilder.Replace you may want to look into Regex.Replace. That way you can do somthing like:

Regex.Replace("Input string", "aaa", match => "bbb");

Very similar to what you want to do, just out the box.

Answer 6

It is a little unclear how you're going to use this - since the example you've posted is trivial, I have to ask ts there any particular reason it needs to be an anonymous method? Couldn't it just be a regular instance method instead?

Answer 7

You have to use extension method to achive the expected..

since the default StringBuilder.replace doesnt accept Func<>, you have to create the extension method replace which meets your requirement

here the sample code.

public static class ExtensionMethods
{
          public static StringBuilder  replace(this StringBuilder Sb1,string input, 
          Func<string> anonymos)
          {
               return Sb1.Replace(input, anonymos.Invoke());
          }
}

and you have to invoke the extension replace method like this

        StringBuilder s1 = new StringBuilder();
        s1.Append("hai");
        s1.replace("hai", () =>
        {
            return "bb";
        });

hope this helps.

Cheers

Ramesh Vel