[R] How to get warning about implicit factor to integer coercion?

[WB Kloke]

Is there a way in R (12.x) to avoid the implicit coercion of factors to integers
in the context of subscripts?

If this is not possible, is there a way to get at least a warning, if any
coercion of this type happens, given that the action of this coercion is almost
never what is wanted?

Of course, in the rare case that as.integer() is applied explicitly onto a
factor, the warning is not needed, but certainly not as disastrous as in the
other case.

Probably, in a future version of R, an option similar to that for partial
matches of subscripts might be useful to change the default from maximal
unsafety to safe use.