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use crate::element::Element;
use crate::Symbol;
// This macro defines a new iterator type for a given `Iterator => Item` type name pair.
//
// The implementation produced can be used to iterate over any `Vec<Item>` or `&[Item]`.
macro_rules! create_new_slice_iterator_type {
    ($($iterator_name:ident => $item_name:ty),+) => ($(
        // Define a new type called '$iterator_name' that's a thin wrapper around a slice iterator.
        // We wrap the slice iterator in an `Option` so we can provide the functionality of an empty
        // iterator without requiring that an empty Vec or slice be provided. This sidesteps some
        // hairy lifetime issues.
        pub struct $iterator_name<'a> {
            values: Option<std::slice::Iter<'a, $item_name>>
        }

        impl<'a> $iterator_name<'a> {
            // Define a constructor that takes a slice of `Item`
            pub(crate) fn new(data: &'a [$item_name]) -> Self {
                $iterator_name {
                    values: Some(data.iter()),
                }
            }

            // Define a constructor that takes no parameters and returns an empty iterator
            pub(crate) fn empty() -> $iterator_name<'static> {
                $iterator_name { values: None }
            }
        }

        // Implement the Iterator trait for our new type
        impl<'a> Iterator for $iterator_name<'a> {
            type Item = &'a $item_name;

            fn next(&mut self) -> Option<Self::Item> {
                self.values.as_mut().and_then(|iter| iter.next())
            }
        }
    )*)
}
create_new_slice_iterator_type!(
    // Used for iterating over an Element's annotations
    SymbolsIterator => Symbol,
    // Used for iterating over a Sequence's Elements
    ElementsIterator => Element
);

/// Consuming iterator for [`Annotations`](crate::element::Annotations).
#[derive(Debug, Clone)]
pub struct AnnotationsIntoIter {
    into_iter: std::vec::IntoIter<Symbol>,
}

impl AnnotationsIntoIter {
    pub(crate) fn new(into_iter: std::vec::IntoIter<Symbol>) -> Self {
        Self { into_iter }
    }
}

impl Iterator for AnnotationsIntoIter {
    type Item = Symbol;

    fn next(&mut self) -> Option<Self::Item> {
        self.into_iter.next()
    }
}