/// Returns the id of the previous half-edge in the adjacent face or `None` if the half-edge is at the boundary of the mesh
/// or if the walker has walked outside of the mesh at some point.
Returns the id of the previous half-edge in the adjacent face or `None` if the half-edge is at the boundary of the mesh
or if the walker has walked outside of the mesh at some point.
Returns the id of the previous half - edge in the adjacent face or ` None ` if the half - edge is at the boundary of the mesh or if the walker has walked outside of the mesh at some point .
pub fn previous_id(&self) -> Option<HalfEdgeID>
    {
        if let Some(next_id) = self.next_id() { Walker::new(&self.connectivity_info).into_halfedge_walker(next_id).next_id() }
        else { None }
    }
pub fn previous_id ( & self ) -> Option < HalfEdgeID > { if let Some ( next_id ) = self . next_id ( ) { Walker :: new ( & self . connectivity_info ) . into_halfedge_walker ( next_id ) . next_id ( ) } else { None } }
Returns the id of the previous half-edge in the adjacent face or `None` if the half-edge is at the boundary of the mesh
or if the walker has walked outside of the mesh at some point.
Returns the id of the previous half - edge in the adjacent face or ` None ` if the half - edge is at the boundary of the mesh or if the walker has walked outside of the mesh at some point .
&self