Steven, James, >there are 22 implementations of RelShuttleImpl(excluding tests)
14 of them are RelHomogeneousShuttle subclasses. RelHomogeneousShuttle redirects all customized visit methods into a single visit(RelNode) method. That means Calcite has only 6 usages (!) of the "visitor" feature, and the feature basically forces ALL RelNodes implement an obscure RelNode#accept. The method is ill-defined. Here's its javadoc: "Accepts a visit from a shuttle" It makes no sense at all. How should I implement this? @return A copy of this node incorporating changes made by the shuttle to * this node's children None of Calcite's RelNode implementations walk over children or something when implementing accept(RelShuttle). ---- The only non-test, non-homogeneous subclasses are: ToLogicalConverter RelNodesExprsHandler SqlToRelConverter#convertSelectImpl # "attach hint to the first Hintable rel" RelOptMaterialization#tryUseStar ViewTable#expandView I do not know if those classes require any of the "visitor" features, however, it is clear that the half-visitor is complicating things more often than it helps. Vladimir
