rust - Idiomatic way to use a computed value as a pattern in match -

what best way use value computed @ runtime 1 of patterns in match?

i have value (byte) need match against other values. of values fixed (b'0'..b'9'). others computed @ runtime (c = some_function()).

my current solution use fake variable , if guard (i.e. k if (k == c)), not nice me. tried using c gets interpreted catch-all variable, rather substituted value of c in context.

the following code snippet shows problem: (also on playpen)

fn main() {     fun(b'5', 0);     fun(b'c', 0);     fun(b'c', 2); }  fn fun(byte: u8, i: uint) {     let chars = b"abcdefgh";     let c = chars[i];      let msg = match byte {         b'0'..b'9' => "numeric",         // c => "same char", // <-- had preferred         k if (k == c) => "same char",         _ => "different char",     };      println!("fun({}, {} [{}]) = {}", byte, i, c, msg); } 

is idiomatic construct rust can offer?

in short, yes, should use pattern guards this.

to make possible there should way differentiate plain bindings , equality checks. scala, example, based on variable case: if starts capital letter, equality check; otherwise pattern binding. there no such mechanism in rust, no, impossible now.