Extension error assignment, how to fix?

Question

We suppose that for example i have a string, and i want to escape it, and to be well reading)

need a working extension what will solve this problem

i tried.

var t = "'";
t.Escape();// == "%27" (what i need), but it not assign result to var. t
t = t.Escape();//works, but ugly.

and the extension

public static string Escape(this string string_2)
    {
        if (string_2.HasValue())
            string_2 = Uri.EscapeDataString(string_2);
        return string_2;
    }

how to fix this extension be working?

Strings are immutable in .NET. You need to assign new value to variable anyway. — Sergey Berezovskiy, Jun 07 '13 at 11:53
Strings are immutable, and you can't use `ref` with extension methods, so - you can't do it. — Blorgbeard, Jun 07 '13 at 11:53
Also, given that strings *are* immutable, a `t.Escape()` method that somehow did modify `t` would be the ugly syntax, since no other string method works that way! — Blorgbeard, Jun 07 '13 at 11:54

score 5 · Accepted Answer · edited May 23 '17 at 12:11

t = t.Escape(); is the usual idiom in .NET for changing a string. E.g. t = t.Replace("a", "b"); I'd recommend you use this. This is necessary because strings are immutable.

There are ways around it, but they are uglier IMO. For example, you could use a ref parameter (but not on an extension method):

public static string Escape (ref string string_2) { ... }
Util.Escape(ref t);

Or you could make your own String-like class that's mutable:

public class MutableString { /** include implicit conversions to/from string */ }
public static string Escape (this MutableString string_2) { ... }

MutableString t = "'";
t.Escape();

I'd caution you that if you use anything besides t = t.Escape();, and thus deviate from normal usage, you are likely to confuse anyone that reads the code in the future.

with another class "helper" i thought), anyway, will remain "ugly" variant :). thx. — Daniel, Jun 07 '13 at 11:59

Matthew Watson · Answer 2 · 2013-06-07T13:58:33.540

1

"Mutable string" in C# is spelled StringBuilder.

So you could do something like this:

public static void Escape(this StringBuilder text)
{
    var s = text.ToString();
    text.Clear();
    text.Append(Uri.EscapeDataString(s));
}

But using it wouldn't really be that great:

StringBuilder test = new StringBuilder("'");
test.Escape();
Console.WriteLine(test);

The real answer is to use the "ugly" string reassignment

t = t.Escape();//works, but ugly.

You'll get used to it. :)

edited Jun 07 '13 at 13:58

answered Jun 07 '13 at 12:25

Matthew Watson

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[Offtopic] is your avatar image related to Douglas Adams ? :) – Cristian Diaconescu Jun 07 '13 at 14:49
@CristiDiaconescu Haha yes it is - well spotted. :) – Matthew Watson Jun 07 '13 at 14:59

Extension error assignment, how to fix?

2 Answers2