R Under development (unstable) (2024-01-23 r85822 ucrt) -- "Unsuffered Consequences"
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> message("TESTING: extend()...")
TESTING: extend()...
> 
> library("R.oo")
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.26.0 successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, load, save

> 
> setConstructorS3("MyDouble", function(value=0, ...) {
+   extend(as.double(value), "MyDouble", ...)
+ })
> 
> setMethodS3("as.character", "MyDouble", function(object, ...) {
+   fmtstr <- attr(object, "fmtstr")
+   if (is.null(fmtstr))
+     fmtstr <- "%.6f"
+   sprintf(fmtstr, object)
+ })
NULL
> 
> setMethodS3("print", "MyDouble", function(object, ...) {
+   print(as.character(object), ...)
+ })
NULL
> 
> x <- MyDouble(3.1415926)
> print(x)
[1] "3.141593"
> 
> x <- MyDouble(3.1415926, fmtstr="%3.2f")
> print(x)
[1] "3.14"
> attr(x, "fmtstr") <- "%e"
> print(x)
[1] "3.141593e+00"
> 
> 
> 
> 
> 
> 
> setConstructorS3("MyList", function(value=0, ...) {
+   extend(list(value=value, ...), "MyList")
+ })
> 
> setMethodS3("as.character", "MyList", function(object, ...) {
+   fmtstr <- object$fmtstr
+   if (is.null(fmtstr))
+     fmtstr <- "%.6f"
+   sprintf(fmtstr, object$value)
+ })
NULL
> 
> setMethodS3("print", "MyList", function(object, ...) {
+   print(as.character(object), ...)
+ })
NULL
> 
> x <- MyList(3.1415926)
> print(x)
[1] "3.141593"
> x <- MyList(3.1415926, fmtstr="%3.2f")
> print(x)
[1] "3.14"
> x$fmtstr <- "%e"
> print(x)
[1] "3.141593e+00"
> 
> message("TESTING: extend()...DONE")
TESTING: extend()...DONE
> 
> proc.time()
   user  system elapsed 
   0.31    0.09    0.35