Idea for more flexible access to relations

[geoneutrino]

Discussed in #540

^{Originally posted by geoneutrino September 22, 2023}
Hello,

way_function in lua is normally a lot of calls to sub-functions to process the different types of elements/layers needed (streets, landuse, boundaries, labels ...)

when accepting multiple type of relations the current concept is a bit unclean from a software engineering perspective:
Accessing relations in one of those sub-functions with the while .. NextRelation() loop mentioned in the docs/RELATIONS.md results in the relationSubscript variable incremented in OsmLuaProcessing::NextRelation() until the end of the list and afterwards i can never reset it to use again in another function

tilemaker/src/osm_lua_processing.cpp

Line 522 in 439c6b1

kaguya::optional<int> OsmLuaProcessing::NextRelation() {

An easy improvement for this scenario would be to expose a simple "ResetRelationSubscript" method in osm_lua_processing to set relationSubscript to -1

A more complex but maybe also useful in the future would be to expose methods for accessing the relations in a more flexible way, kind of dictionary e.g. add a method NextRelationOfType("abc") that loops overs relations with attribute type=abc

Thanks

[systemed]

Have a look at #548 - does this fix it for you?

[geoneutrino]

looks good