Messages in this thread | | | From | Miguel Ojeda <> | Date | Thu, 10 Aug 2023 01:22:15 +0200 | Subject | Re: [PATCH] rust: macros: add `paste!` proc macro |
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On Wed, Jun 28, 2023 at 7:12 PM Gary Guo <gary@garyguo.net> wrote: > > This macro provides a flexible way to concatenated identifiers together > and it allows the resulting identifier to be used to declare new items, > which `concat_idents!` does not allow. It also allows identifiers to be > transformed before concatenated. > > The `concat_idents!` example > > let x_1 = 42; > let x_2 = concat_idents!(x, _1); > assert!(x_1 == x_2); > > can be written with `paste!` macro like this: > > let x_1 = 42; > let x_2 = paste!([<x _1>]); > assert!(x_1 == x_2); > > However `paste!` macro is more flexible because it can be used to create > a new variable: > > let x_1 = 42; > paste!(let [<x _2>] = [<x _1>];); > assert!(x_1 == x_2); > > While this is not possible with `concat_idents!`. > > This macro is similar to the `paste!` crate [1], but this is a fresh > implementation to avoid vendoring large amount of code directly. Also, I > have augmented it to provide a way to specify span of the resulting > token, allowing precise control. > > For example, this code is broken because the variable is declared inside > the macro, so Rust macro hygiene rules prevents access from the outside: > > macro_rules! m { > ($id: ident) => { > // The resulting token has hygiene of the macro. > paste!(let [<$id>] = 1;) > } > } > > m!(a); > let _ = a; > > In this versionn of `paste!` macro I added a `span` modifier to allow > this: > > macro_rules! m { > ($id: ident) => { > // The resulting token has hygiene of `$id`. > paste!(let [<$id:span>] = 1;) > } > } > > m!(a); > let _ = a; > > Link: http://docs.rs/paste/ [1] > Signed-off-by: Gary Guo <gary@garyguo.net>
Applied to `rust-next` with the SPDX license identifier added as discussed and the typo fixed -- thanks everyone!
Cheers, Miguel
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