[R-pkg-devel] Three-argument S3method declaration does not seem to affect dispatching from inside the package.

[Pavel Krivitsky]

Hi, Inaki,

On Tue, 2019-05-14 at 12:50 +0200, Iñaki Ucar wrote:
> The thing is that, in R, "nearer" means "the calling environment"
> (and then, other things). When you call test_me(), the calling
> environment for gen() is the package namespace. When you call gen()
> directly, thenthe calling environment is the global environment. So
> what happens here follows the principle of least astonishment.

I don't think that we disagree about which environment takes
precedence. The issue is whether *within a a given environment*,
registration or function naming should take precedence.

> The issue here is that you are registering a non-standard name
> (.gen.formula) for that generic and then defining what would be the
> standard name (gen.formula) for... what purpose? IMHO, this is a bad
> practice and should be avoided.

The situation initially arose when I wanted to soft-deprecate calling a
particular method by its full name in order to clean up the package's
namespace.

To use our working example, I wanted calls to gen.formula() to issue a
deprecation warning, but calls to gen(formula) not to. The simplest way
to do that that I could find was to create a function, say,
.gen.formula() that would implement the method and declare it as the S3
export, and modify gen.formula() to issue the warning before passing on
to .gen.formula(). Then, direct calls to gen.formula() would produce a
warning, but gen(formula) would by pass it.

> > That is, for a call from inside a package, the order of precedence
> > would be as follows:
> >    1. S3method() in that package's NAMESPACE.
> >    2. Appropriately named function in that package (exported or
> > not).
> >    3. Appropriately named function in calling environment (which
> > may be
> >       GlobalEnv).
> >    4. S3method() in other loaded packages' NAMESPACEs.
> >    5. Appropriately named functions exported by other loaded
> > packages'
> >       NAMESPACEs.
> > 
> > For a call from outside a package, the precedence is the same, but
> > 1 and 2 are not relevant.
> > 
> > As far as I can tell, this is the current behaviour except for the
> > relative ordering of 1 and 2.
> 
> Nope. Current behaviour (see details in ?UseMethod) is:
> 
> "To support this, UseMethod and NextMethod search for methods in two
> places: in the environment in which the generic function is called,
> and in the registration data base for the environment in which the
> generic is defined".

Can you be more specific where the sequence above contradicts the
current implementation (except for swapping 1 and 2)? As far as I can
tell, it's just a more concrete description of what's in the
documentation.

			Best Regards,
			Pavel

-- 
Pavel Krivitsky
Lecturer in Statistics
National Institute of Applied Statistics Research Australia (NIASRA)
School of Mathematics and Applied Statistics | Building 39C Room 154
University of Wollongong NSW 2522 Australia
T +61 2 4221 3713
Web (NIASRA): http://niasra.uow.edu.au/index.html
Web (Personal): http://www.krivitsky.net/research
ORCID: 0000-0002-9101-3362

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