const Edge &get_edge(Side s) const { return edges[s]; }
void add_constraint(Widget &, Layout::ConstraintType, Side);
void add_constraint(Widget &, Layout::ConstraintType, const Edge &);
const Edge &get_edge(Side s) const { return edges[s]; }
void add_constraint(Widget &, Layout::ConstraintType, Side);
void add_constraint(Widget &, Layout::ConstraintType, const Edge &);