As_bytes() in match?

help
1

I have $($item:ident),* as input for my macro_rules! and want generate match statement for function:

fn match_x(bytes: &[u8]) -> Foo {
   match bytes {
      b"One" => Foo::One,
      b"Two" => Foo::Two,
      _ => Foo::Unknown,
   }
}

But I can not find way to solve it, I tried this:

match bytes {
    $(stringify!($item).as_bytes() => Foo::$item,)*
    _ => Foo::Unknown,
}

but compiler do not like .as_bytes() call in match.
That is rather strange because of as_bytes is const function.

I also tried b stringify!($item) and bstringify!($item),
but all this is wrong conceptions.
Any way to use get bytes from ident and compiler happy?

2 
$(
    #[allow(nonstandard_style)]
    const $item: &[u8] = stringify!($item).as_bytes();
)*
match bytes {
$(
    | $item => Foo::$item,
)*
    | _ => Foo::Unknown,
}

More generally, bstringify! can be trivially implemented with a procedural macro.

So that's what I've done: feel free to use it!

2 Likes
3

Thank you for answer, I don't even think into this direction (defining const).

If I remember correctly some time ago Rust compiler interpret named constant in match as variable/alias declaration,
like:

match x {
 y => { (1) }
}

inside (1) y is new variable equal to x.
But looks like this was fixed some time ago?

4

This topic was automatically closed 90 days after the last reply. We invite you to open a new topic if you have further questions or comments.