How do I extend the String class?

Question

Extending core classes in javascript is dead easy. I get the impression it's not quite so easy in C#. I was wanting to add some things to the String class so that I could do stuff like:

string s = "the cat's mat sat";
string sql = s.smartsingleQuote();

thus giving me

the cat''s mat sat

Is that even feasible, or do I have to write a function for that?

score 12 · Answer 1 · edited Sep 08 '13 at 05:48

12

Yes it is possible using Extension Methods - MSDN

Here is a sample code.

public static class Extns
{
    public static string smartsingleQuote(this string s)
    {
        return s.Replace("'","''");
    }
}

Disclaimer : Not tested.

edited Sep 08 '13 at 05:48

Tushar Gupta - curioustushar

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answered Aug 22 '13 at 04:25

Anuraj

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score 3 · Answer 2 · edited May 23 '17 at 10:25

3

You cannot accomplish exactly what you are talking about as the string class is sealed

You can accomplish the aesthetic of this by creating an extension method

public static class StringExtensions
{
  public static string SmartSingleQuote(this string str)
  {
    //Do stuff here
  }
}

The this keyword in the parameter allows you to take that parameter and put it in front of the method name for easier chaining like you requested done in your question. This, however, is equivalent to:

StringExtensions.SmartSingleQuote(s);

It just depends on your preference at that point :)

Here is a good SO answer on extension methods

edited May 23 '17 at 10:25

Community

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answered Aug 22 '13 at 04:26

Justin Pihony

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If you are using extension method, you can directly call s.SmartSingleQuote() right? If you are using StringExtensions.SmartSingleQuote(s), you don't require an extension method right? – Anuraj Aug 22 '13 at 04:32
@Anuraj yes, I did not re-hash that as that was part of the OP's question, which was already answered. I was trying to give a deeper understanding of extension methods to understand what it is equivalent to – Justin Pihony Aug 22 '13 at 04:33

redtuna · Accepted Answer · 2013-08-22T18:52:48.913

Yes you can do this, with an extension method. It'll look something like that:

public static class NameDoesNotMatter {
   public static string smartSingleQuote(this string s) {
      string result = s.Replace("'","''");
      return result;
   } 
}

The magic is the keyword "this" in front of the first argument. Then you can write your code and it'll work:

string s = "the cat's mat sat";
string sql = s.smartsingleQuote();

How do I extend the String class?

3 Answers3