I’ve got the following scenario: I need to store information about an R function, and retrieve it at a later point. In other programming languages I’d implement this using a dictionary with the functions as keys. In R, I’d usually use `attr(f, 'some-name')`. However, for my purposes I do not want to use `attr` because the information that I want to store is an implementation detail that should be hidden from the user of the function (and, just as importantly, it shouldn’t clutter the display when the function is printed on the console).
`comment` would be almost perfect since it’s hidden from the output when printing a function — unfortunately, the information I’m storing is not a character string (it’s in fact an environment), so I cannot use `comment`. How can this be achieved? For reference, I’ve considered the following two alternatives: 1. Use `attr`, and override `print.function` to not print my attribute. However, I’m wary of overriding a core function just to implement such a little thing, and overriding this function would obviously clash with other overrides, if somebody else happens to have a similarly harebrain idea. 2. Use C++ to retrieve the SEXP to the body of the CLOSXP that represents a function, and use that as a key in a dictionary. I *think* that this robustly and efficiently identifies functions in R. However, this relies quite heavily on R internal implementation details, and in particular on the fact that the GC will not move objects around in memory. The current GC doesn’t do this but Gábor Csárdi rightfully pointed out to me that this might change. On the chance that I’m trying to solve the wrong Y to an X/Y problem, the full context to the above problem is explained in [1]. In a nutshell, I am hooking a new environment into a function’s parent.env chain, by re-assigning the function’s `parent.env` (naughty, I know): ``` parent.env(my_new_env) = parent.env(f) parent.env(f) = my_new_env ``` This is done so that the function `f` finds objects defined inside that environment without having to attach it globally. However, for bookkeeping purposes I need to preserve the original parent environment — hence the question. [1]: https://github.com/klmr/modules/issues/66 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
