Generics and Methods

Object-Oriented Programming with S3 and R6 in R

Richie Cotton

Data Evangelist at DataCamp

summary(c(TRUE, FALSE, NA, TRUE))

   Mode   FALSE    TRUE    NA's 
logical       1       2       1

summary(rgamma(1000, 1))

    Min.  1st Qu.   Median     Mean  3rd Qu.     Max. 
0.000354 0.276500 0.690300 1.020000 1.384000 9.664000

function overloading = input-dependent

function behavior

ch2_1-generics-and-methods.007.png

ch2_1-generics-and-methods.008.png

ch2_1-generics-and-methods.009.png

ch2_1-generics-and-methods.010.png

print

function (x, ...) 
UseMethod("print")
<bytecode: 0x1062f0870>
<environment: namespace:base>

Methods are named generic.class

print.Date
summary.factor
unique.array

Method signatures contain generic signatures

args(print)

function (x, ...) 
NULL

args(print.Date)

function (x, max = NULL, ...) 
NULL

pass arguments between methods with `...`

include it in both generic and methods

print.function

function (x, useSource = TRUE, ...) 
.Internal(print.function(x, useSource, ...))

print.Date

function (x, max = NULL, ...) 
{
    if (is.null(max)) 
        max <- getOption("max.print", 9999L)
    if (max < length(x)) {
        print(format(x[seq_len(max)]), max = max, ...)
        cat(" [ reached getOption(\"max.print\") -- omitted", 
            length(x) - max, "entries ]\n")
    }
    else print(format(x), max = max, ...)
    invisible(x)
}