StackOverflowException on recursive anonymous functions

Question

I'm trying to write a function to check whether a string is a palindrome, and using this example, I'm trying to reverse the string using a recursive anonymous function:

static Boolean checkPalindromeAnonRec(string str)
{
    str = str.ToLower().Replace(" ", String.Empty);
    Func<string, string> revStr = null;
    revStr = delegate(string s) 
      { 
        if (s.Length > 1) 
          { return revStr(s) + s[0]; } 
        else 
        { return s; } 
      };

    return (str == revStr(str));
}

But every time I run it I get a StackOverflowException. It's not obvious to me why, any ideas?

Jon Skeet · Accepted Answer · 2013-07-12 19:05:44Z

5

Well this is the problem:

if (s.Length > 1) 
  { return revStr(s) + s[0]; }

Aside from the odd bracing style, that's just recursing with the original string - so it will keep going forever. I suspect you meant to use Substring somewhere so that it recursed using a shorter string...

I would actually try writing it as a simple non-anonymous (but still recursive) method to start with - so work out how you would recursively write:

static string Reverse(string input)

... then if you still want to inline that into your CheckPalindrome method, you can do so.

answered Jul 12, 2013 at 19:05

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Jellezilla Over a year ago

How embarassing. Should have been return revStr(s.Substring(1)) + s[0] all along.

Jellezilla Over a year ago

Just tried it out. It actually performs better with a named function than with the anonymous function

Alexei Levenkov Over a year ago

+1. And when you are done with fixing code make it properly anonymous recursion: Anonymous Recursion in C#

Collectives™ on Stack Overflow

StackOverflowException on recursive anonymous functions

1 Answer 1

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related