removeEdge method
Implementation
@override
void removeEdge(Node parent, Node child) {
_guardGraphContainsNode(parent, extra: '(parent)');
_guardGraphContainsNode(child, extra: '(child)');
_parents.remove(child);
final firstEdges = _edges.putIfAbsent(parent, () => {});
firstEdges.remove(child);
if (firstEdges.isEmpty) {
_edges.remove(parent);
}
}