[Rd] (PR#7320) Internal function isUME() in findGeneric() is wrong

[Prof Brian Ripley]

The issue is the use of UseMethod(), which you claim to be valid.  As it
is inconsistent with the prime documentation, the help page, I would
question if it is `perfectly legal'.  I expect the author of isUME
implemented the behaviour described on the help page.

It is documented in S-PLUS as *strongly discouraged*, and although it is
documented in R-lang, I believe the right thing to do is to make the code
agree with the prime documentation.

I see no uses of UseMethod() in the R sources, and on CRAN only
one in a comment (and none in BioC).

On Thu, 28 Oct 2004 jhallman at frb.gov wrote:

> Full_Name: Jeff Hallman
> Version: 2.0
> OS: Linux
> Submission from: (NULL) (132.200.32.34)
> 
> 
> The function findGeneric() in the utils namespace contains this internal
> function:
> 
>   isUME <- function(e) {
>         if (is.call(e) && (is.name(e[[1]]) || is.character(e[[1]]))) {
>             switch(as.character(e[[1]]), UseMethod = as.character(e[[2]]), 
>                 "{" = isUMEbrace(e), "if" = isUMEif(e), "")
>         }
>         else ""
>     }
> 
> This fails if the generic called UseMethod() without an argument, which is
> perfectly legal.  Changing it to this seems to work:
> 
>   isUME <- function(e) {
>     if(is.call(e) &&(is.name(e[[1]]) || is.character(e[[1]]))) {
>       switch(as.character(e[[1]]), 
>              UseMethod = ifelse(length(e) == 1, fname, as.character(e[[2]])), 
>              "{" = isUMEbrace(e),
>              "if" = isUMEif(e),
>              "")
>     }
>     else ""
>   }
> 
> 
> Jeff
> 
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> 
> 

-- 
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)
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