kdy1 / is-macro Goto Github PK

The macro currently generates as_variant(), returning Option<&T>. Could it also generate as_mut_variant(), returning Option<&mut T>?

Minimal reproducible example:

use is_macro::Is;

#[derive(Debug, Is)]
enum Foo {
    A(u8),
    B(u8, u8)
}

fn main() {
    println!("Hello, world!");
}

error[E0023]: this pattern has 1 field, but the corresponding tuple variant has 2 fields
 --> src\main.rs:3:17
  |
3 | #[derive(Debug, Is)]
  |                 ^^ expected 2 fields, found 1
...
6 |     B(u8, u8),
  |     --------- tuple variant defined here

error: aborting due to previous error

While we're adopting is-macro in tbot, we found that translation to snake_case may yield a bit unexpected results around digits. For this enum, I would expect that the generated is_ method would be named is_video_mp4, not is_video_mp_4 (notice the underscore before the number):

#[derive(Is)]
pub enum MimeType {
    …
    /// The `video/mp4` MIME type.
    VideoMp4,
}

Such cases should probably be left to humans, because one might actually expect an underscore inserted between a word and a digit. I suggest an attribute, setting which changes the generated method names:

#[derive(Is)]
pub enum MimeType {
    …
    #[is(root = "video_mp4")]
    VideoMp4,
}

With this attribute, Is would generate is_video_mp4 instead of is_video_mp_4. If it were possible for this variant, it would also emit expect_video_mp4 and video_mp4 instead of expect_video_mp_4 and video_mp_4. This can be extended in the future with ability to choose names for each method or change their prefixes. The only downside to this is a more complicated implementation. Also, if this is going to be implemented, we should probably come up with a better name than root.

(by the way, we really appreciate this crate for generating expect_ and taking methods, and also that we don't have to manually implement is_ methods 😀)

Minimal reproducible example:

use is_macro::Is;

#[derive(Is)]
enum Foo {
    A(&'static u8),
}

error: proc-macro derive panicked
 --> src\main.rs:3:10
  |
3 | #[derive(Is)]
  |          ^^
  |
  = help: message: Quote::parse() failed.
                          Note: quasi quotting was invoked from:
                 D:\Tools\Rust\cargo\registry\src\github.com-1ecc6299db9ec823\is-macro-0.1.1\src\lib.rs:131:45

          Error from syn: expected identifier
              >>>>>
                  & 'static u8
              <<<<<