Question

浏览Hadley Wickham的S4维基： 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")

我们如何为Person设计构造函数（像这样）

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

不这样做：

> 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

在你的例子中看起来答案就在那里：

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

产量

> 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

然而，这是相当un-S4并且重复了在类定义中已经分配的默认值。也许你更愿意做

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

并且牺牲了没有命名参数的调用能力？

Answer 2

我希望给最终用户一些关于参数类型的提示，而不是@themel使用...的建议。同时放弃原型并使用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R的向量化结构，并使用{{1在构造函数中，所以派生类也可以使用构造函数。

...

和

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, ...)

S4构造函数和原型

2 个答案: