r - 如何在 R 中创建虚拟引用类？

Question

我在 help(ReferenceClasses) 中找不到关于虚拟/抽象类的太多信息- 任何人都可以提供一个创建一个的基本示例吗？此外，如何指定虚拟方法并强制子类必须实现它？

Answer 1

引用类是 S4 类。所以也许你应该看看 setClass 的帮助和 Classes :
这是一个虚拟示例:

# virtual Base Class
setRefClass( 
  Class="virtC", 
  fields=list( 
    .elt="ANY" 
  ),
  methods = list(
    .method = function(){
      print("Base virtual method is called")
    }
  ), 
  contains=c("VIRTUAL") 
) 
   
## child 1
## field as numeric and base .method is used
setRefClass( 
  Class="childNum", 
  fields=list( 
    .elt="numeric" 
  ), 
  contains=c("virtC")  
)


## child 2 
## field is char and .method is overwritten
setRefClass( 
  Class="childChar", 
  fields=list( 
    .elt="character" 
  ), 
  methods = list(
    .method = function(){print('child method is called')}
  ), 
  contains=c("virtC") 
) 
##  new('virtA')          ## thros an error can't isntantiate it
a = new("childChar",.elt="a")
b =   new("childNum",.elt=1)

b$.method()
[1] "Base virtual method is called"

a$.method()
[1] "child method is called"