Discussion: deprecate Lwt.ignore_result

[aantron]

@Drup in #332 (comment):

(well, Lwt.ignore_result is also a serious anti-pattern and people should probably never use it, but that's another discussion :p)

What is the reason for that? Should it be deprecated in favor of, say, Lwt.async?

[Drup]

At the very least, I think it should be made very clear in the documentation that this function gives no guarantee whatsoever about when the ignored bit will be executed.

[aantron]

Right, I've likewise seen usage where the user clearly meant >>= fun _ -> or >|= ignore >>= fun () -> instead.

[aantron]

This will be accomplished by #469 ("New reference docs for module Lwt"), which moves ignore_result to the very bottom of the docs, into section Deprecated, subsection Miscellaneous. It explains the reason for deprecation. It doesn't add an annotation, because I'm guessing it's not worth annoying existing users over, but I may be wrong here.