pub fn and_modify<F: FnOnce(&mut V)>(mut self, f: F) -> Self {
        match &mut self {
            Entry::Vacant(_) => {}
            Entry::Occupied(entry) => f(entry.get_mut()),
        }
        self
    }
Provides in-place mutable access to an occupied entry before any potential inserts into the
map.
crates/core/executor/src/memory.rs