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#![feature(generic_associated_types, associated_type_defaults)]
use std::borrow::Borrow;
use std::ops::Deref;
pub trait MapGuard<'a, T>: Deref + std::marker::Sized {}
impl<'a, T> MapGuard<'a, T> for &'a T where T: 'a {}
pub trait Map<K, V> {
type GetGuard<'a>: MapGuard<'a, V>;
fn get<'a, Q: ?Sized>(&'a self, k: &Q) -> Option<Self::GetGuard<'a>> where K: Borrow<Q>;
fn insert(&mut self, k: K, v: V) -> Option<V>;
}
#[cfg(test)]
mod tests {
use super::*;
fn assert_map_get<K, V>(map: impl Map<K, V>, k: K, v: V) {
assert_eq!(map.get(&k), Some(v));
}
fn assert_map_insert<K, V>(map: impl Map<K, V>, k: K, v: V, o: Option<V>) {
assert_eq!(map.insert(k, v), o);
}
}