On 3/12/20 4:06 PM, William Dunlap wrote:
Note that substitute(...()) and substitute(someFunc(...))[-1] give
slightly different results, the former a pairlist and the latter a call.
> str((function(...)substitute(...()))(stop(1),stop(2),stop(3)))
Dotted pair list of 3
$ : language stop(1)
$ : language stop(2)
$ : language stop(3)
>
str((function(...)substitute(someFunc(...))[-1])(stop(1),stop(2),stop(3)))
language stop(1)(stop(2), stop(3))
Yes, I am aware of this difference. In my use cases, the ...() form
gives the result that I prefer (a pairlist).
The ...() idiom has been around for a long time, but more recently
(slightly after R-3.4.0?) the ...elt(n) and ...length() functions were
introduced so you don't have to use it much.
Yes, I know both.
I don't see a ...names()
function that would give the names of the ... arguments -
names(substitute(...())).
Exactly, this is a frequent use case. Occasionally I use it in other
cases as well where I deliberately do not want to evaluate the arguments
passed as dots.
What I am most interested in is whether this is a 'trick' or a legal use
of a (rather unadvertised) feature of the language.
Bill Dunlap
TIBCO Software
wdunlap tibco.com <http://tibco.com>
On Thu, Mar 12, 2020 at 2:09 AM Dénes Tóth <toth.de...@kogentum.hu
<mailto:toth.de...@kogentum.hu>> wrote:
Dear R Core Team,
I learnt approx. two years ago in this mailing list that one can use
the
following "trick" to get a (dotted pair)list of the ellipsis arguments
inside a function:
`substitute(...())`
Now my problem is that I can not find any occurrence of this call
within
the R source - the most frequent solution there is
`substitute(list(...))[-1L] `
I would like to know if:
1) substitute(...()) is a trick or a feature in the language;
2) it will be supported in the future;
3) when (in which R version) it was introduced.
A hint on where to look for the machinery in the R source would be also
appreciated.
Regards,
Denes
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