[feature request] Add `pattern` argument to `watcher`

[vorpalvorpal]

It would be nice for watcher to have a pattern argument so that one could (for example), just monitor .log files or .html files within a folder.

I looked at the source, but its all R6 and c++ so I don't think I can offer a PR for the feature unfortunately.

This is possibly somewhat related to issue 14.

[shikokuchuo]

It's often more efficient to monitor an entire directory rather than a collection of individual files.

The intent is that you check for the extensions as part of your callback function - it is called back with the vector of files that have changed. You can then condition any action on the type of file changed.

If this doesn't work for your use case, do let us know.

[vorpalvorpal]

The callback works fine, but it just ends up that I have a bunch of repeated code that checks if the file fits some particular pattern, and I thought it might make sense to move that code back one step. I'll probably just create a wrapper around watcher instead. Thank you.