R7: A first look

1. Hadley Wickham on behalf of 
 The R Consortium Working Group on OOP 
 https://rconsortium.github.io/OOP-WG/ R7: A fi rst look at a new OOP system for R June 2022
2. bizarro < - function(x) { if (is.numeric(x)) { - x } else if (is.logical(x)) { !x } else if (is.character(x)) { str_reverse(x) } else if (is.factor(x)) { levels(x) < - rev(level(x)) x } else { stop("Not supported") } } Why do we need OOP? This is even more important for functions in base R, like print()
3. S3 S4 English Fairy Tales (1918) by Flora Annie Steel, illustrated by Arthur Rackham R7 R7 = S3 + S4
4. library(R7) bizarro < - new_generic("bizarro", "x") With R7, we fi rst de fi ne a generic Name of the generic Name of the argument used for dispatch
5. method(bizarro, class_numeric) < - function(x) { - x } method(bizarro, class_logical) < - function(x) { !x } method(bizarro, class_character) < - function(x) { str_reverse(x) } Then we de fi ne methods Name of the generic Built-in class
6. bizarro #> <R7_generic> function (x, . . . ) with 4 methods: #> 1 : method(bizarro, "integer") #> 2 : method(bizarro, "double") #> 3 : method(bizarro, "character") #> 4 : method(bizarro, "logical")
7. bizarro(1) #> [1] -1 bizarro(TRUE) #> [1] FALSE bizarro(mean) #> Error: generic `bizarro()` can't f i nd method #> for function object
8. Generics de fi ne behaviour Classes de fi ne data
9. range < - new_class("range", properties = list( start = class_numeric, end = class_numeric ) ) Creating a new class Name of the class Property type Property name Constructor function
10. x < - range(start = 1, end = 10) x #> <range> #> @ start: num 1 #> @ end : num 10 x@start x@end < - 20 x@end < - "x" #> Error: <range>@end must be <double>, not <character>
11. r < - range(start = 10, end = 1) 
 #> <range> #> @ start: num 10 #> @ end : num 1 But…
12. range < - new_class("range", properties = . . . , validator = function(self) { if (length(self@start) ! = 1) { "@start must be length 1" } else if (length(self@end) ! = 1) { "@end must be length 1" } else if (self@end < self@start) { "@end must be greater than or equal to @start" } } ) Can add a validator to prevent that from happening
13. range < - new_class("range", properties = list( start = class_double, end = class_double, length = new_property( getter = function(self) self@end - self@start, ) ), … ) Can also create dynamic properties
14. S3 S4 English Fairy Tales (1918) by Flora Annie Steel, illustrated by Arthur Rackham R7
16. 1. Team e ff ort. 2. Formal de fi nition of class and properties (like S4). 3. Embrace data access. 4. Backward compatible with S3. 5. Pit of success. Why do we hope this will succeed?
17. Please try it out! https://rconsortium.github.io/OOP-WG/ remotes : : install_github("rconsortium/OOP-WG") What doesn’t work? 
 What don’t you understand? These slides at https://speakerdeck.com/hadley/r7-a- fi rst-look