Github user felixcheung commented on a diff in the pull request:
https://github.com/apache/spark/pull/14558#discussion_r74694116
--- Diff: R/pkg/R/functions.R ---
@@ -1143,7 +1139,7 @@ setMethod("minute",
#' @export
#' @examples \dontrun{select(df, monotonically_increasing_id())}
setMethod("monotonically_increasing_id",
- signature(x = "missing"),
+ signature(),
--- End diff --
Hmm, I looked into this a bit
in below, "a" is what we have orginially
```
setGeneric("a", function(x) { standardGeneric("a") } )
setMethod("a", signature(x = "missing"), function() { 1 })
> a()
[1] 1
> a(1)
Error in (function (classes, fdef, mtable) :
unable to find an inherited method for function âaâ for signature
â"numeric"â
> showMethods(a)
Function: a (package .GlobalEnv)
x="missing"
setGeneric("b", function(x = "missing") { standardGeneric("b") } )
setMethod("b", signature("missing"), function() { 1 })
> b()
[1] 1
> b(1)
Error in (function (classes, fdef, mtable) :
unable to find an inherited method for function âbâ for signature
â"numeric"â
> showMethods(b)
Function: b (package .GlobalEnv)
x="missing"
setGeneric("tt", function(...) { standardGeneric("tt") } )
setMethod("tt", signature(), function() { 1 })
> tt(1)
Error in .local(...) : unused argument (1)
> tt("emme")
Error in .local(...) : unused argument ("emme")
> showMethods(tt)
Function: tt (package .GlobalEnv)
...="ANY"
...="character"
(inherited from: ...="ANY")
...="numeric"
(inherited from: ...="ANY")
```
I think the issue with `setMethod("foo", signature(), function() { 1 })`
are two folds:
1. The error message when calling the function with a parameter is less
clear than "unable to find function for signature â"numeric"â"
2. S4 method is automatically generated for each parameter type that it is
called with (see "numeric" or character" from showMethods)
So perhaps "b" is a better approach?
Unfortunately we still have to "document" a parameter or `...` in either
case as `setGeneric` refuse to take it otherwise.
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