Function derive_utils::derive_trait

pub fn derive_trait<I>(
    data: &EnumData, 
    trait_path: Path, 
    supertraits_types: I, 
    trait_def: ItemTrait
) -> TokenStream where
    I: IntoIterator<Item = Ident>,
    I::IntoIter: ExactSizeIterator, 

A function for creating proc_macro_derive like deriving trait to enum so long as all variants are implemented that trait.

Examples

use derive_utils::derive_trait;
use proc_macro::TokenStream;
use quote::format_ident;
use syn::{parse_macro_input, parse_quote};

#[proc_macro_derive(Iterator)]
pub fn derive_iterator(input: TokenStream) -> TokenStream {
    derive_trait(
        &parse_macro_input!(input),
        // trait path
        parse_quote!(std::iter::Iterator),
        // super trait's associated types
        None,
        // trait definition
        parse_quote! {
            trait Iterator {
                type Item;
                fn next(&mut self) -> Option<Self::Item>;
                fn size_hint(&self) -> (usize, Option<usize>);
            }
        },
    )
    .into()
}

#[proc_macro_derive(ExactSizeIterator)]
pub fn derive_exact_size_iterator(input: TokenStream) -> TokenStream {
    derive_trait(
        &parse_macro_input!(input),
        // trait path
        parse_quote!(std::iter::ExactSizeIterator),
        // super trait's associated types
        Some(format_ident!("Item")),
        // trait definition
        parse_quote! {
            trait ExactSizeIterator: Iterator {
                fn len(&self) -> usize;
            }
        },
    )
    .into()
}