Is there a way to make “destructive” string methods a-la Ruby?

Question

In Ruby, methods which change the object have a bang on the end: string.downcase!

In c# you have to do: foo = foo.ToLower()

Is there a way to make an extension method like:

foo.ConvertToLower()

that would manipulate foo?

(I think the answer is no since strings are immutable and you can't do a ref this in an extension method.)

Answer 1

No, you cannot do this in an extension method. To reassign the value of a variable passed in as a parameter you have to pass it by reference using the ref parameter modifier, what is not allowed for extension methods. Even if this would be possible, there might not be a variable to reassign, like in "foo".ConvertToLower().

Answer 2

There are two ways of mutating a string instance:

• Reflection
• Unsafe code

I wouldn't recommend using either of them. Your fellow developers will hate you forever - particularly if the method is ever used to change a string which happens to be a literal...

Answer 3

You can certainly write an extension method to re-assign the string being operated on. For example:

public static void ConvertToLower(this string s)
{
   s = s.ToLower();
}

This has nothing to do with the immutability of strings.