R Under development (unstable) (2024-01-23 r85822 ucrt) -- "Unsuffered Consequences"
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> 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

> 
> message("TESTING: Interface...")
TESTING: Interface...
> 
> int <- Interface()
> print(int)
[1] "Interface"
> 
> setConstructorS3("MyInterface", function(...) {
+   extend(Interface(), "MyInterface")
+ })
> int <- MyInterface()
> print(int)
[1] "MyInterface, Interface"
> 
> setConstructorS3("MyClass", function(...) {
+   extend(Object(), c("MyClass", uses(MyInterface(), Interface())))
+ })
> obj <- MyClass()
> print(obj)
[1] "MyClass: 0x00000296a2439108"
> 
> 
> ## For some reason uses(<string>) doesn't play well with covr
> if (!"covr" %in% loadedNamespaces()) {
+   setConstructorS3("MyClass", function(...) {
+     extend(Object(), c("MyClass", uses("MyInterface", "Interface")))
+   })
+   obj <- MyClass()
+   print(obj)
+ }
[1] "MyClass: 0x000002969ee1d530"
> 
> message("TESTING: Interface...DONE")
TESTING: Interface...DONE
> 
> proc.time()
   user  system elapsed 
   0.29    0.07    0.36