[R] Method dispatch for function call operator?
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@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.
Re: [R] Method dispatch for function call operator?
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(...)- y
You 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?
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Re: [R] Method dispatch for function call operator?
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@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, rip...@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, UKFax: +44 1865 272595 __ R-help@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.
Re: [R] Method dispatch for function call operator?
Thank you both for very helpful answers. I have indeed missed the help pages
about ( and now the situation is more clear.
You 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.
Unfortunately, it won't work as assignment function form treats the first
argument specially. My intention was to create syntactic sugar like
x$metadata(condition) - newvalue
instead of
x$setMetadata(condition, value=newvalue)
I know that
metadata(x, condition) - newvalue
would work, but I would like to avoid that particular syntax for a number of
reasons.
Well, you can't have everything, I guess. I'll just stick to the []
operator.
Thanks again for the clarification!
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[R] Method dispatch for function
How can I determine what S3 method will be called for a particular
first-argument class?
I was imagining something like functionDispatch('str','numeric') =
utils:::str.default , but I can't find anything like this.
For that matter, I was wondering if anyone had written a version of
`methods` which gave their fully qualified names if they were not visible,
e.g.
methods('str') =
utils:::str.data.frameutils:::str.default
stats:::str.dendrogramstats:::str.logLikutils:::str.POSIXt
or
methods('str') =
$utils
str.data.frame str.defaultstr.POSIXt
$stats
str.dendrogram str.logLik
Thank you,
-s
[[alternative HTML version deleted]]
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