add option for required fields

[vgough]

Adds a Verify function on FlagSetFiller, which can be used to check that required fields were set after flags have been parsed.

Required flags are pretty common, so this reduces the amount of boilerplate

[itzg]

Very cool! I had always wanted "required" support but always got stuck in the lack in base flags processing. Didn't dawn on me your novel idea of verifying separately.

Just a very minor change needed.

Thanks!

[vgough]

If you don't want the formatting and lint warning fixes (reflect.Ptr -> reflect.Pointer, interface{} -> any), then feel free to pull out the parts you want, I don't mind. I could have ignored the lint warnings, just seemed easy enough to fix them while I was poking around.

[itzg]

If you don't want the formatting and lint warning fixes (reflect.Ptr -> reflect.Pointer, interface{} -> any), then feel free to pull out the parts you want, I don't mind. I could have ignored the lint warnings, just seemed easy enough to fix them while I was poking around.

Those changes are great. It's good to get the code more modernized.

[itzg]

Released/tagged in https://github.com/itzg/go-flagsfiller/releases/tag/v1.17.0