S4 构造函数和原型

Question

浏览 Hadley Wickham 的 S4 wiki： https://github.com/hadley/devtools/wiki/S4

setClass("Person", representation(name = "character", age = "numeric"), 
  prototype(name = NA_character_, age = NA_real_))
hadley <- new("Person", name = "Hadley")

我们如何设计Person 的构造函数（像这样）

Person<-function(name=NA,age=NA){
 new("Person",name=name,age=age)
}

不执行此操作：

> Person()
Error in validObject(.Object) : 
  invalid class "Person" object: 1: invalid object for slot "name" in class "Person": got class "logical", should be or extend class "character"
invalid class "Person" object: 2: invalid object for slot "age" in class "Person": got class "logical", should be or extend class "numeric"

Answer 1

看起来答案就在您的示例中：

Person<-function(name=NA_character_,age=NA_real_){
 new("Person",name=name,age=age)
}

yield

> Person()
An object of class "Person"
Slot "name":
[1] NA

Slot "age":
[1] NA

> Person("Moi")
An object of class "Person"
Slot "name":
[1] "Moi"

Slot "age":
[1] NA

> Person("Moi", 42)
An object of class "Person"
Slot "name":
[1] "Moi"

Slot "age":
[1] 42

但是，这相当不符合 S4，并且重复了类定义中已分配的默认值。也许您更愿意

Person <- function(...) new("Person",...)

牺牲不带命名参数的调用能力？

Answer 2

我更愿意为最终用户提供一些有关参数类型的提示，而不是建议使用 @themel 的 ... 。还放弃原型并使用 length(x@name) == 0 作为字段未初始化的指示，使用 People 类而不是 Person，反映了 R 的向量化结构，并在构造函数中使用 ...，因此派生类也可以使用构造函数。

setClass("People",
    representation=representation(
        firstNames="character",
        ages="numeric"),
    validity=function(object) {
        if (length(object@firstNames) != length(object@ages))
            "'firstNames' and 'ages' must have same length"
        else TRUE
    })

People = function(firstNames=character(), ages=numeric(), ...)
    new("People", firstNames=firstNames, ages=ages, ...)

和

People(c("Me", "Myself", "I"), ages=c(NA_real_, 42, 12))