Method Lookup for Primitive Generics

Object-Oriented Programming with S3 and R6 in R

Richie Cotton

Data Evangelist at DataCamp

Writing code
Debugging code
Maintaining code

Running code

R vs. C

C code often runs faster
R code is usually easier to write
... and easier to debug

ch2_3-method-lookup-for-primitive-generics.012.png

ch2_3-method-lookup-for-primitive-generics.013.png

exp

function (x)  .Primitive("exp")

function (e1, e2)  .Primitive("+")

if

.Primitive("if")

sin

function (x)  .Primitive("sin")

function (e1, e2)  .Primitive("-")

for

.Primitive("for")

.S3PrimitiveGenerics

"anyNA"          "as.character"   "as.complex"
"as.double"      "as.environment" "as.integer"     
"as.logical"     "as.call"        "as.numeric"
"as.raw"         "c"              "dim"           
"dim<-"          "dimnames"       "dimnames<-"     
"is.array"       "is.finite"      "is.infinite"    
"is.matrix"      "is.na"          "is.nan"
"is.numeric"     "length"         "length<-"      
"levels<-"       "names"          "names<-"
"rep"            "seq.int"        "xtfrm"

all_of_time <- c("1970-01-01", "2012-12-21")
as.Date(all_of_time)

"1970-01-01" "2012-12-21"

class(all_of_time) <- "date_strings"
as.Date(all_of_time)

Error in as.Date.default(all_of_time) : 
  do not know how to convert 'all_of_time' to class"Date"

length(all_of_time)

Summary

Some R functions are actually written in C
The primitive interface gives best performance
.S3PrimitiveGenerics lists primitive S3 generics
Primitive generics don't throw an error when no method is found

Let's practice!

Object-Oriented Programming with S3 and R6 in R