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Implement #[distance(fallback)] for #[derive(ComputeSquaredDistance)]

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This commit is contained in:
Anthony Ramine 2017-08-26 18:13:40 +02:00
parent 4faadb489f
commit 41c3be54ea
3 changed files with 49 additions and 51 deletions
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21
components/style_derive/compute_squared_distance.rs
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@ -4,15 +4,16 @@
use animate::AnimationVariantAttrs;
use cg;
use quote;
use syn;
use quote::Tokens;
use syn::{DeriveInput, Path};
pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
pub fn derive(input: DeriveInput) -> Tokens {
let name = &input.ident;
let trait_path = &["values", "distance", "ComputeSquaredDistance"];
let (impl_generics, ty_generics, mut where_clause) =
cg::trait_parts(&input, trait_path);
let input_attrs = cg::parse_input_attrs::<DistanceInputAttrs>(&input);
let variants = cg::variants(&input);
let mut match_body = quote!();
let mut append_error_clause = variants.len() > 1;
@ -45,7 +46,13 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
}));
if append_error_clause {
match_body = quote! { #match_body, _ => Err(()), };
if let Some(fallback) = input_attrs.fallback {
match_body.append(quote! {
(this, other) => #fallback(this, other)
});
} else {
match_body.append(quote! { _ => Err(()) });
}
}
quote! {
@ -63,3 +70,9 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
}
}
}
#[darling(attributes(distance), default)]
#[derive(Default, FromDeriveInput)]
struct DistanceInputAttrs {
fallback: Option<Path>,
}