[yladiz]

An issue with $ReadOnlyArray is that if you're doing something that does work on both String and Number types, like using them for some template string, Flow will complain that the types are not compatible even though in this instance they are. This is a bigger issue with both TypeScript and Flow, in that they don't seem to keep enough track of the data in arrays, only the type of the array, to know if the actual types are valid. If TypeScript/Flow kept track of the array elements and their usage, this issue wouldn't occur in the same way.