Make provider classes finalised

[vicchi]

All provider class constructors should be finalised; see #531 (comment) for context.

[unkind]

For clarity, the original discussion was about classes.

[Nyholm]

Why would we make providers final? I guess some people extend our provider class to just to some minor change.

Also, we can not make GoogleMaps final because our GoogleMapsBusiness inherits form that. Same with Nominatim and OpenStreetMap.

[unkind]

Also, we can not make GoogleMaps final because our GoogleMapsBusiness inherits form that. Same with Nominatim and OpenStreetMap.

Why they use inheritance? Why GoogleMaps can't have optional named constructor like business, e.g. GoogleMaps::business() with clientId and privateKey? Why OpenStreetMap extends Nominatim, just for default value of rootUrl? Is it possible to replace it with Nominatim::defaultServer() or simply pass it from configuration file?

Why would we make providers final? I guess some people extend our provider class to just to some minor change.

In general, inheritance should be avoided in favour of composition.

If you look at the providers, in most cases they don't have any protected members, there is no place for inheritance here. If somebody still wants to use it, he probably makes design mistake. Do you really want to keep BC for users with design issues?

After all, in case of emergency, if user needs to fix something quick, he can create completely new implementation by copy-pasting original one. And he also can send patch for new extension point of existing provider or bugfix.

[willdurand]

I like the idea of making the providers final but as @Nyholm said, we have inheritance for some providers. Maybe we could compose these providers instead of using inheritance, but it might not be worth doing it.

[Nyholm]

I do not have an opinion in the matter. Im just asking =)

I like your arguments @unkind. Do you want to make a PR trying to solve the GoogleMaps/Nominatim issues or should I?

@willdurand: We can try and see if it is worth doing. =)

[Nyholm]

Closed by #540