Matching against a u8 with char literal

[Valloric]

Boiled down, here's the problem I have:

let f: u8 = '\n' as u8;
let b: u8 = match f { 
  '\n' => 1, 
   _ => 2
};

I'm parsing some binary data and a u8 value in some cases might be an ASCII char. I'd love to be able to match against these with char literals, but the compiler complains. My actual code is more complicated and involves matching ['\\', 'x', c1, c2, ..] (and similar patterns) against a &[u8] slice.

Possible solutions might involve something like allowing casts in the pattern ('\n' as u8 => ...). A more generic solution might be to just have a macro that takes a char literal and returns a u8. So something like foo!('\n') would expand to 10.

Either that, or string literals à la C++11: u8'\n'.

[huonw]

Dupe of #4334 (specifically #4334 (comment)).

You can use a static as a (rather verbose) work-around:

static N: u8 = '\n' as u8;
match f {
     N => 1,
     _ => 2,
}

[sfackler]

This also works:

let f: u8 = '\n' as u8;
let b: u8 = match f as char {
    '\n' => 1,
    _ => 2
};

[Valloric]

You can use a static as a (rather verbose) work-around

That's exactly what I'm doing right now. It's really verbose.

@sfackler Matching as char means I'd have to limit the value to being a valid char, which it might not be.

[sfackler]

All values from 0 to 255 are valid chars. That's why you can cast from u8 to char, but not from u32 to char.

[Valloric]

@sfackler Hm, I thought UTF-8 made some of those values special...

Still, what I'm actually matching against is a &[u8] with an array pattern and this doesn't help there. But I'll keep it in mind since it might come in handy later, thanks.

[thestinger]

@Valloric: char is a UCS4 code point, and those values are valid but not all encoded as a single byte in UTF-8

[teknopaul]

Since this thread comes top in Google, rust has byte literals that can be compared C style with ==

if c == b'\n' { 
    ...

[leifmetcalf]

Since this thread comes top in Google, rust has byte literals that can be compared C style with ==

if c == b'\n' { 
    ...

This should be a help message for expected `u8`, found `char`