How to extend C# built-in types, like String?

Greetings everyone... I need to Trim a String. But I want to remove all the repeated blank spaces within the String itself, not only at the end or at the start of it. I could do it with a method like:

public static string ConvertWhitespacesToSingleSpaces(string value)
{
    value = Regex.Replace(value, @"\s+", " ");
}

Which I got from here. But I want this piece of code to be called within the String.Trim() itself, so I think I need to extend or overload or override the Trim method... Is there a way to do that?

Thanks in advance.

Since you cannot extend string.Trim(). You could make an Extension method as described here that trims and reduces whitespace.

namespace CustomExtensions
{
    //Extension methods must be defined in a static class
    public static class StringExtension
    {
        // This is the extension method.
        // The first parameter takes the "this" modifier
        // and specifies the type for which the method is defined.
        public static string TrimAndReduce(this string str)
        {
            return ConvertWhitespacesToSingleSpaces(str).Trim();
        }

        public static string ConvertWhitespacesToSingleSpaces(this string value)
        {
            return Regex.Replace(value, @"\s+", " ");
        }
    }
}

You can use it like so

using CustomExtensions;

string text = "  I'm    wearing the   cheese.  It isn't wearing me!   ";
text = text.TrimAndReduce();

Gives you

text = "I'm wearing the cheese. It isn't wearing me!";

Is it possible? Yes, but only with an extension method

The class System.String is sealed so you can't use overriding or inheritance.

public static class MyStringExtensions
{
  public static string ConvertWhitespacesToSingleSpaces(this string value)
  {
    return Regex.Replace(value, @"\s+", " ");
  }
}

// usage: 
string s = "test   !";
s = s.ConvertWhitespacesToSingleSpaces();

There's a yes and a no to your question.

Yes, you can extend existing types by using extension methods. Extension methods, naturally, can only access the public interface of the type.

public static string ConvertWhitespacesToSingleSpaces(this string value) {...}

// some time later...
"hello world".ConvertWhitespacesToSingleSpaces()

No, you cannot call this method Trim(). Extension methods do not participate in overloading. I think a compiler should even give you a error message detailing this.

Extension methods are only visible if the namespace containing the type that defines the method is using'ed.

Extension methods!

public static class MyExtensions
{
    public static string ConvertWhitespacesToSingleSpaces(this string value)
    {
        return Regex.Replace(value, @"\s+", " ");
    }
}

How to extend C# built-in types, like String?

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