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R7: A first look

R7: A first look

7ba164f40a50bc23dbb2aa825fb7bc16?s=128

Hadley Wickham

June 21, 2022
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  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
  15. None
  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
  18. None