C#•14mo ago

✅ How to pattern-match a `Rune`?

is this the best I can do?

myRune switch
{
    _ when myRune == (Rune)'A' => 3,
    _ when myRune == (Rune)'B' => 4,
    // ...
}

myRune switch
{
    _ when myRune == (Rune)'A' => 3,
    _ when myRune == (Rune)'B' => 4,
    // ...
}

That's very noisy visually and it's unclear to me if the compiler is smart enough to perform the (Rune) cast on char literals at compile-time. Is there not a way to specify a constant/literal Rune value?

29 Replies

Thinker•14mo ago

Rune is firstly very old I think and secondly has no kind of compiler/runtime support, so no it has no constant representation

__dil__OP•14mo ago

One one think that since it's the way to represent valid utf-16 scalars and that it is old (according to you, I have no idea), that it would have decent language support, no? 🤔 do c# devs just not care about supporting basic utf-16?

Thinker•14mo ago

char is UTF-16

__dil__OP•14mo ago

utf-16 scalars can be made of one or two chars which is what rune represents is that not correct?

Jimmacle•14mo ago

at least for me, my tasks that involve parsing just don't have to handle non-ascii characters

__dil__OP•14mo ago

that's fair, but in a world of international communication things tend to be more complex than that in general

Jimmacle•14mo ago

is there something specific you're trying to achieve?

__dil__OP•14mo ago

I think that's stated in the original question, let me know if I can clarify 🙂

Jimmacle•14mo ago

i mean the overall goal

__dil__OP•14mo ago

I need to parse strings that may contain any valid utf-16 scalar

Jimmacle•14mo ago

do you need to specifically handle characters that may be 2 code units? or is the fact that they may exist in the input irrelevant to the actual parsing logic

reflectronic•14mo ago

here is something you can do:

internal static class RuneExtensions
{
      public static void Deconstruct(this Rune rune, out char? character)
      {
          if (rune.Utf16SequenceLength == 1)
          {
              // For a non-surrogate, the UTF-16 code unit has the value of the code point
              character = (char)rune.Value;
          }
          else
          {
              character = null;
          }
      }
}

internal static class RuneExtensions
{
      public static void Deconstruct(this Rune rune, out char? character)
      {
          if (rune.Utf16SequenceLength == 1)
          {
              // For a non-surrogate, the UTF-16 code unit has the value of the code point
              character = (char)rune.Value;
          }
          else
          {
              character = null;
          }
      }
}

Thinker•14mo ago

yeah was about to suggest that

reflectronic•14mo ago

then you can pattern match as follows:

var m = rune switch
{
    Rune('A') => 100,
    Rune('N') => 200,
    Rune(null) => -1
};

var m = rune switch
{
    Rune('A') => 100,
    Rune('N') => 200,
    Rune(null) => -1
};

i assume you do not need to match on actual surrogate pairs, though you can add another overload of Deconstruct to do that

__dil__OP•14mo ago

interesting!

Thinker•14mo ago

didn't know Deconstruct allowed you to use that pattern matching syntax

__dil__OP•14mo ago

Bear in mind I come from a place where you don't have to ask this question since char is a whole scalar, not half of it. So the answer is "I don't know because I don't know which characters are part of the extended set or not". Now, I'm aware the pragmatic answer is "if you don't know, then you probably don't need it". Nonetheless, I've been learning a lot by studying these more complex situations. It allows me to see different corners of the languages and the techniques that are used to work with them. reflectronic's answer looks like it covers exactly what I need in this regard

reflectronic•14mo ago

there are not many commonly-used symbols that are not in the Basic Multilingual Plane (the set of characters which can be encoded with one UTF-16 code unit) so most people in C# will cook up the most cursed string processing algorithms in existence, largely because the APIs are not very good, and nobody will notice

__dil__OP•14mo ago

yeah that makes sense

reflectronic•14mo ago

it is mostly historical scripts outside of the BMP. there are some mathematical symbols which are probably used more often than those. there are also many emoji 😂 is probably the most common non-BMP character

__dil__OP•14mo ago

That is good to know! Definitely niche in the context of parsing, but good to know nonetheless. In the context of general string manipulation this is paramount though since you need to be careful not to break up surrogate pairs. @reflectronic if you don't mind me asking, how long have you been learning C#, and do you work professionally with it?

reflectronic•14mo ago

i'm not a professional, just a college sophomore :) as for how long, it's hard to say, it's been at least three or four years, before that i was sort of on-and-off with programming

__dil__OP•14mo ago

You've been answering a bunch of my more obscure questions, so I figure you're pretty familiar with the language. I was curious how long it might take to develop said familiarity.

reflectronic•14mo ago

one could say that, uh, my life skill tree is not very balanced

__dil__OP•14mo ago

wdym? lots of CS?

reflectronic•14mo ago

many people have been using C# for far longer than me, but are probably more familiar with very different, more practical, things about the language

__dil__OP•14mo ago

ah I see. Well, I can relate to you in a sense. I'm not a dev by trade (actually graduated in physics), so programming is more like a fun puzzle/hobby for me. Recently I've been thinking about becoming a dev though. which is part of why I'm learning C#. Not a ton of Rust jobs in my area.

reflectronic•14mo ago

i like to understand how things work and read about the reasons why things are the way they are, it is very fun for me, and there is certainly a great depth of knowledge that comes from that. i am not sure how useful it is, or if other people like to do the same thing

Accord•14mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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✅ How to pattern-match a `Rune`?