How do I use an extension function in another class? C#

Question

I've got a couple of extension functions that I want to transfer between classes.

I have a class called Helpers.cs that I want to have the following:

namespace XYZ
{
    public class Helpers
    {
        public static string Encrypt(this string plainText){
            //... do encrypting
        }
    }
}

In my other class Impliment.cs I want to have the following:

string s = "attack";
s.Encrypt();

How can I implement this?

Answer 1

You're close - extension methods need to be in a static class:

public static class Helpers
{
    public static string Encrypt(this string plainText){
        //... do encrypting
    }
}

If you tried what you posted you'd get a pretty clear compiler error that says basically the same thing:

Extension method must be defined in a non-generic static class

Note that your usage will be slightly different that what you want. You can't do:

string s = "attack";
s.Encrypt();

becasue strings are immutable. Best you can do is overwrite the existing varialbe or store the result in a new one:

string s = "attack";
s = s.Encrypt();  // overwrite

or

string s = "attack";
string s2 = s.Encrypt();  // new variable