Better to use enum class instead of enum

[jievince]

eg. In s2shape_index.h:

enum InitialPosition { BEGIN, END, UNPOSITIONED };

Such an enum name like BEGIN is very common, so it is easy to have the same name with a macro or other enum, which will cause conflict.

[jievince]

If changing it to enum class is ok, I will make a PR to fix it.

[jmr]

Sure. You can call them kBegin, etc.

[jmr]

I mean, send a PR to change it to:

enum class InitialPosition { kBegin, kEnd, kUnpositioned };

[jievince]

OK