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use syn::parse::Error;
use syn::spanned::Spanned;
/// Return the value that fulfills the predicate if there is one in the slice. Panic if there is
/// more than one.
pub fn find_only<T, F>(iter: impl Iterator<Item = T>, pred: F) -> Result<Option<T>, Error>
where
T: Spanned,
F: Fn(&T) -> Result<bool, Error>,
{
let mut result = None;
for item in iter {
if pred(&item)? {
if result.is_some() {
return Err(Error::new(item.span(), "Multiple defaults"));
}
result = Some(item);
}
}
Ok(result)
}