parent.frame(1) of a S4 method is not a calling environment.

Duncan Murdoch <murdoch.duncan at gmail.com> writes:

Vitaly S. wrote:

Martin Morgan <mtmorgan at fhcrc.org> writes:

So, ?can I be sure that for such functions parent.frame(2) will always work?
What are the additional rules?

callNextMethod() will cause additional problems; the idea that you'll
grab things from somewhere other than function arguments doesn't seem
like a robust design, even if it's used in some important parts of R.

Martin

That make it difficult to handle unevaluated expressions in methods. A solution
would be to explicitly require the users to use quote() or expression(), ?and
then to use the "expression" in the signature. Slightly unpleasant, though.

You could use formulas for that. ?If you pass in

formula = ~ x + y*z

then environment(formula) will be the right evaluation environment, and formula[[2]] will be the unevaluated x +
y*z.

Duncan Murdoch

Thank you Duncan, I didn't know that.

For programmatic use though, formula interface is slightly inconvenient. A
specialized function and class would be desirable. With the advent of more and
more complex S4 classes, unevaluated expressions in methods calls will became a
necessity, that's my feeling.