/// Allocate a new node ID that has not yet been used.
Allocate a new node ID that has not yet been used.
Allocate a new node ID that has not yet been used .
pub fn alloc_id(&mut self) -> NodeId {
        let id = NodeId::new(self.next_id);
        self.next_id += 1;
        id
    }
pub fn alloc_id ( & mut self ) -> NodeId { let id = NodeId :: new ( self . next_id ) ; self . next_id += 1 ; id }
Allocate a new node ID that has not yet been used.
Allocate a new node ID that has not yet been used .
&mut self