doc: method and class definition order matters

[JosiahParry]

When defining S7 classes and methods, the order matters whereas typically this is not the case.

For example, in types.R I have a Todo definition

Todo <- S7::new_class(
  "Todo",
  properties = list(
 ...
  ),
)

In data-frame-methods.R I have a method defined:

method(as.data.frame, Todo) <- function(x, ...) {
  data.frame(
     ...
  )
}

This causes an error when using devtools::load_all()

Error in `load_all()`:
! Failed to load R/data-frame-methods.R
Caused by error:
! object 'Todo' not found

I believe this is because of the collation order putting data-frame-methods.R before types.R. The fix is to either change the file names or to put the method definition after the class definition.

Perhaps recommendations can be made in "Generics and methods"?

[sounkou-bioinfo]

i Second adding docs related to this

[ltuijnder]

My current approach to solve this is adding "class stubs" definitions in file named: AAA_class_stubs.R or something.

As far as I known, this was the current recommended approach mentioned here: #250 (comment)

Though class stubs have the downside that they do not play nice with LSP's and code tooling. But indeed it can be documented better because it is surprising behavior for package developers. Though this is simply how R works. And what I understood from the above link is that people using S4 have the same problem. So its not unique to S7.