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use darling::{FromDeriveInput, FromMeta};
#[derive(FromMeta, PartialEq, Eq, Debug)]
enum Volume {
Whisper,
Talk,
Shout,
}
/// A more complex example showing the ability to skip at a field or struct
/// level while still tracking which type parameters need to be bounded.
/// This can be seen by expanding this example using `cargo expand`.
#[derive(FromMeta)]
#[allow(dead_code)]
enum Emphasis<T> {
Constant(Volume),
Variable(darling::util::PathList),
#[darling(skip)]
PerPhoneme(Option<T>),
Strided {
#[darling(skip)]
step: Vec<T>,
#[darling(multiple)]
volume: Vec<Volume>,
},
}
#[derive(FromDeriveInput)]
#[darling(attributes(speak))]
struct SpeakingOptions<T, U> {
max_volume: U,
#[darling(skip, default)]
additional_data: Vec<T>,
}
#[derive(Default)]
struct Phoneme {
#[allow(dead_code)]
first: String,
}
// This is probably the holy grail for `darling`'s own internal use-case:
// Auto-apply `Default` bound to skipped *field* types in `where` clause.
impl<T, U> Default for SpeakingOptions<T, U>
where
Vec<T>: Default,
U: Default,
{
fn default() -> Self {
Self {
max_volume: Default::default(),
additional_data: Default::default(),
}
}
}
fn main() {
let derive_input = syn::parse_str(
r#"
#[derive(Speak)]
#[speak(max_volume = "shout")]
enum HtmlElement {
Div(String)
}
"#,
)
.unwrap();
let parsed: SpeakingOptions<Phoneme, Volume> =
FromDeriveInput::from_derive_input(&derive_input).unwrap();
assert_eq!(parsed.max_volume, Volume::Shout);
assert_eq!(parsed.additional_data.len(), 0);
}
|
