syn 0.15.16

use proc_macro2::TokenStream;
use quote::ToTokens;

pub struct TokensOrDefault<'a, T: 'a>(pub &'a Option<T>);

impl<'a, T> ToTokens for TokensOrDefault<'a, T>
where
    T: ToTokens + Default,
{
    fn to_tokens(&self, tokens: &mut TokenStream) {
        match *self.0 {
            Some(ref t) => t.to_tokens(tokens),
            None => T::default().to_tokens(tokens),
        }
    }
}