1use syn::parse::Error;
2use syn::spanned::Spanned;
3
4/// Return the value that fulfills the predicate if there is one in the slice. Panic if there is
5/// more than one.
6pub fn find_only<T, F>(iter: impl Iterator<Item = T>, pred: F) -> Result<Option<T>, Error>
7where
8 T: Spanned,
9 F: Fn(&T) -> Result<bool, Error>,
10{
11 let mut result: Option = None;
12 for item: T in iter {
13 if pred(&item)? {
14 if result.is_some() {
15 return Err(Error::new(item.span(), message:"Multiple defaults"));
16 }
17 result = Some(item);
18 }
19 }
20 Ok(result)
21}
22