I was tasked to implement the CachingConditionResolver, which is used in QueryPlanningTraversal.
The TypeScript version of QueryPlanningTraversal has a field conditionResolver, which is a closure that captures this (QueryPlanningTraversal) as mutable reference and calls this.resolveConditionPlan. The problem is that there is a cyclic reference structure: QueryPlanningTraversal -owns-> conditionResolver -captures-> QueryPlanningTraversal.
In Rust, CachingConditionResolver can't mutably reference QueryPlanningTraversal, since we want QueryPlanningTraversal to hold the CachingConditionResolver itself. (Not considering smart pointers or unsafe references)
Proposed Solution
I decided not to implement CachingConditionResolver. Instead, I made QueryPlanningTraversal to implement ConditionResolver trait directly and hold its own cache. I separated the caching logic in the newConditionResolverCache struct. But, the separation of caching and resolver is not as nice as the TypeScript version.
An alternative solution would be to create a wrapper struct that holds both QueryPlanningTraversal and a cache. But, then every references of QueryPlanningTraversal needs to be changed to point to the new wrapper. I didn't think it'd be worthwhile, only to gain a slightly better separation and reusability.
Background
I was tasked to implement the
CachingConditionResolver, which is used inQueryPlanningTraversal. The TypeScript version ofQueryPlanningTraversalhas a fieldconditionResolver, which is a closure that capturesthis(QueryPlanningTraversal) as mutable reference and callsthis.resolveConditionPlan. The problem is that there is a cyclic reference structure:QueryPlanningTraversal-owns->conditionResolver-captures->QueryPlanningTraversal.In Rust,
CachingConditionResolvercan't mutably referenceQueryPlanningTraversal, since we wantQueryPlanningTraversalto hold theCachingConditionResolveritself. (Not considering smart pointers or unsafe references)Proposed Solution
I decided not to implement
CachingConditionResolver. Instead, I madeQueryPlanningTraversalto implementConditionResolvertrait directly and hold its own cache. I separated the caching logic in the newConditionResolverCachestruct. But, the separation of caching and resolver is not as nice as the TypeScript version.An alternative solution would be to create a wrapper struct that holds both
QueryPlanningTraversaland a cache. But, then every references ofQueryPlanningTraversalneeds to be changed to point to the new wrapper. I didn't think it'd be worthwhile, only to gain a slightly better separation and reusability.