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/// The trait for a key that can be used to store values in the maps.
pub trait Key<K: 'static, V: 'static>: Copy {
    type Storage: Storage<K, V>;
}

/// The trait defining how storage works.
///
/// # Type Arguments
///
/// - `K` is the key being stored.
/// - `V` is the value being stored.
pub trait Storage<K: 'static, V: 'static>: Default {
    /// This is the storage abstraction for [`Map::insert`](struct.Map.html#method.insert).
    fn insert(&mut self, key: K, value: V) -> Option<V>;

    /// This is the storage abstraction for [`Map::get`](struct.Map.html#method.get).
    fn get(&self, key: K) -> Option<&V>;

    /// This is the storage abstraction for [`Map::get_mut`](struct.Map.html#method.get_mut).
    fn get_mut(&mut self, key: K) -> Option<&mut V>;

    /// This is the storage abstraction for [`Map::remove`](struct.Map.html#method.remove).
    fn remove(&mut self, key: K) -> Option<V>;

    /// This is the storage abstraction for [`Map::clear`](struct.Map.html#method.clear).
    fn clear(&mut self);

    /// This is the storage abstraction for [`Map::iter`](struct.Map.html#method.iter).
    fn iter<'a, F>(&'a self, f: F)
    where
        F: FnMut((K, &'a V));

    /// This is the storage abstraction for [`Map::iter_mut`](struct.Map.html#method.iter_mut).
    fn iter_mut<'a, F>(&'a mut self, f: F)
    where
        F: FnMut((K, &'a mut V));
}