如何在R中創建虛擬參考類？

Question

我無法在help(ReferenceClasses)的虛擬/抽象類中找到太多 - 任何人都可以提供創建一個的基本示例嗎？而且，我怎樣才能指定一個虛擬方法並強制子類必須實現呢？

Answer 1

參考類是S4類。所以也許你應該看到的setClass和Classes幫助：

這裏虛設例如：

# 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 char and .method is overwritten 
setRefClass( 
    Class="childNum", 
    fields=list( 
    .elt="numeric" 
), 
    contains=c("virtC") 
) 


## child 2 
## field is numeric and base .method is used 
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"