Dear R gurus,
I am trying to create a nicer API interface for some R modules I have
written. Here, I heavily rely on S3 method dispatch mechanics and
makeActiveBinding() function
I have discovered that I apparently can't dispatch on function call
operator (). While .Primitive("(") exists, which leads me to believe
that
things like x(...) are internally translated to .Primitive("(")(x,
...), I
can't seem to do something like:
x <- integer()
class(x) <- "testclass"
"(.testclass" <- function(o, x, y) print(paste(x, y))
x(1, 2)
Similar code does work for other operators like "[".
A workaround I have discovered is to make x a function from the beginning
and then extend the functionality by via S3 methods. Unfortunately, it does
not allow me to do something I'd really like to - use syntax like this:
x(...) <- y
For this, I'd need to dispatch on something like
"(<-.testclass" <- function(x, arglist, value)
Currently, I am using the index operator for this (i.e. x[...] <- y) - it
works nicely, but I'd prefer the () syntax, if possible.
Does anyone know a way to do this?
--
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On 11-01-13 3:09 AM, Taras Zakharko wrote:> > Dear R gurus, > > I am trying to create a nicer API interface for some R modules I have > written. Here, I heavily rely on S3 method dispatch mechanics and > makeActiveBinding() function > > I have discovered that I apparently can't dispatch on function call > operator (). While .Primitive("(") exists, which leads me to believe that > things like x(...) are internally translated to .Primitive("(")(x, ...), I > can't seem to do something like:The "(" function is not a function call operator. It's essentially a no-op. I believe its only purpose is to help in deparsing, so that things like (x + y) would deparse in the same way as entered.> > x<- integer() > class(x)<- "testclass" > "(.testclass"<- function(o, x, y) print(paste(x, y)) > x(1, 2) > > Similar code does work for other operators like "[". > > A workaround I have discovered is to make x a function from the beginning > and then extend the functionality by via S3 methods. Unfortunately, it does > not allow me to do something I'd really like to - use syntax like this: > > x(...)<- yYou can use this syntax by defining a function `x<-` <- function(...) {} and it could be an S3 method, but it is a completely separate object from x. Duncan Murdoch> > For this, I'd need to dispatch on something like > > "(<-.testclass"<- function(x, arglist, value) > > Currently, I am using the index operator for this (i.e. x[...]<- y) - it > works nicely, but I'd prefer the () syntax, if possible. > > Does anyone know a way to do this? >
The details here are much more appropriate for R-devel, but please
check the help pages for "(" and "[", and note
- "[" is generic and "(" is not.
- the primitive `(` is used to implement constructions such as
(x <- pi) and not x(...).
The special handling of operators such as "[" is part of the parser,
and you are guessing incorrectly how function calls are parsed.
(Note to Duncan Murdoch whose reply came in whilst I was writig this:
"(" is essentially a no-op, but it does turn visibility on, something
often used with assignments.)
On Thu, 13 Jan 2011, Taras Zakharko wrote:
>
> Dear R gurus,
>
> I am trying to create a nicer API interface for some R modules I have
> written. Here, I heavily rely on S3 method dispatch mechanics and
> makeActiveBinding() function
>
> I have discovered that I apparently can't dispatch on function call
> operator (). While .Primitive("(") exists, which leads me to
believe that
> things like x(...) are internally translated to
.Primitive("(")(x, ...), I
> can't seem to do something like:
>
> x <- integer()
> class(x) <- "testclass"
> "(.testclass" <- function(o, x, y) print(paste(x, y))
> x(1, 2)
>
> Similar code does work for other operators like "[".
>
> A workaround I have discovered is to make x a function from the beginning
> and then extend the functionality by via S3 methods. Unfortunately, it does
> not allow me to do something I'd really like to - use syntax like this:
>
> x(...) <- y
>
> For this, I'd need to dispatch on something like
>
> "(<-.testclass" <- function(x, arglist, value)
>
> Currently, I am using the index operator for this (i.e. x[...] <- y) -
it
> works nicely, but I'd prefer the () syntax, if possible.
>
> Does anyone know a way to do this?
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Method-dispatch-for-function-call-operator-tp3215381p3215381.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595