yield return empty character literal

Question

I'm writing a Linq extension method, to make a p455w0rd from a string input.

public static IEnumerable<char> ToPasswordFormat(this IEnumerable<char> source)
{
        var enumerator = source.GetEnumerator();
        while (enumerator.MoveNext())
        {
            switch((char)enumerator.Current)
            {
                case 'a':
                    yield return '4';
                    break;
                case 'e':
                    yield return '3';
                    break;
                case 'l':
                    yield return '7';
                    break;
                case 'i':
                    yield return '!';
                    break;
                case ' ':
                    yield return '';
                    break;
                default:
                    yield return (char)enumerator.Current;
                    break;
            }
        }
}

as you can see I want to remove spaces, but when I use yield return ''; it gives me error Empty character literal.

What is '' and how can I return yield return nothing?

Just don't yield anything, carry on in your while loop. i.e. `case ' ': break;` — George Duckett, Apr 03 '13 at 13:31
You could return `'\0'`. http://stackoverflow.com/a/3670513/284240 — Tim Schmelter, Apr 03 '13 at 13:33
Rather than using a giant `switch` I suggest you just build a `Dictionary` to map the values; it will be much simpler. — Servy, Apr 03 '13 at 14:00

nvoigt · Accepted Answer · 2013-04-03T13:46:40.943

13

You cannot yield return nothing. The solution would be to not yield return if it's a whitespace. Comment out that line and you should be good.

'' is meaningless. The compiler will complain. There is no such thing as "no character".

edited Apr 03 '13 at 13:46

answered Apr 03 '13 at 13:33

nvoigt

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+1 The key is that given `'1','2',' ','3'` you don't want a sequence like `'1','2','','3'`. You don't want the `' '` replaced with anything at all, so just don't `yield` anything. – George Duckett Apr 03 '13 at 13:36
`There is no such thing as "no character".` Well, actually, there is. `'\0'`. The "null character". That said, it shouldn't be used in this context. – Servy Apr 03 '13 at 13:58
2

The nul character is a valid character. It has a defined value. It has a special meaning for many programming languages, but it's still a character. "No character" cannot exist the same way that "no int" cannot exist, although we frequently speak of "no money" when we mean zero :) – nvoigt Apr 03 '13 at 15:04
@nvoigt No character (or no int) can certainly exist. You would just need to change the type from `char` to `char?`. – svick Apr 03 '13 at 18:17
@svick Even a Nullable char always has a value. It only has an *additional* bool value telling you if the value of the char is useful to you or just random garbage. But it has a value, even a char? cannot have "no value". You can test it, check the value of the char in the nullable char if the HasValue bool is false. It's still a char with a value. – nvoigt Apr 04 '13 at 06:00
@nvoigt Well, that depends on what exactly does “has a value” mean. If you look at it technically, then yeah, it's a `struct` that has a fields set to `false` (so it has a value). But logically, this value represents a state without a value, just like real `null` does for reference types. And most of the time, you care about the logical meaning of code, not about its implementation. – svick Apr 04 '13 at 10:44
@nvoigt, what if I want to do a replace with: Replace('*', '') so that I replace the asterisk with no space. How can I do that? – Kala J Jan 05 '15 at 20:37
@KalaJ That seems to be a different question. You may want to do a search for your question here and if you don't find an answer, post a new question. – nvoigt Jan 06 '15 at 07:55

score 2 · Answer 2 · edited Apr 03 '13 at 18:16

2

'' is meaningless. There is no concept of "no character" - there is the nul character, but it is not the same as "no character". Compare this with strings, which can be a null reference (to a string) or a zero-length string.
Already answered in a comment to your question by @George Duckett: Just remove the yield from the ' ' case.

edited Apr 03 '13 at 18:16

svick

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answered Apr 03 '13 at 13:35

Matthew Watson

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yield return empty character literal

2 Answers2