我开始为工作中的项目修改 R6，但我无法理解以下行为。
假设我定义了一个超类Person和一个子类PersonWithAge：
Person <- R6Class("Person",
public = list(
name = NA,
hair = NA,
initialize = function(name, hair) {
if (!missing(name)) self$name <- name
if (!missing(hair)) self$hair <- hair
self$greet()
},
set_hair = function(val) {
self$hair <- val
},
greet = function() {
cat(paste0("Hello, my name is ", self$name, ".\n"))
}
)
)
PersonWithAge <- R6Class("PersonWithAge",
inherit = Person,
public = list(
age = NA))
如果我尝试向子类添加新方法，则会PersonWithAge收到以下错误：
> PersonWithAge$set("public", "set_age", function(age) self$age <<- age)
Error in self[[group]][[name]] <- value :
invalid type/length (closure/0) in vector allocation
现在，如果我用虚拟方法定义一个新的子类，我可以毫无问题地向子类添加新方法：
PersonWithHeight <- R6Class("PersonWithHeight",
inherit = Person,
public = list(
height = NA,
foo = function() print(1)
))
PersonWithHeight$set("public", "set_height", function(height) self$height <<- height)
> caitlin <- PersonWithHeight$new("Caitlin", "auburn")
Hello, my name is Caitlin.
> caitlin$set_height(165)
> caitlin
<PersonWithHeight>
Public:
foo: function
greet: function
hair: auburn
height: 165
initialize: function
name: Caitlin
set_hair: function
set_height: function
我尝试更改类定义lock中的参数，R6Class但无济于事。会话信息是：
> sessionInfo()
R version 3.1.1 (2014-07-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
locale:
[1] LC_COLLATE=French_France.1252 LC_CTYPE=French_France.1252 LC_MONETARY=French_France.1252 LC_NUMERIC=C
[5] LC_TIME=French_France.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] R6_2.0.1
loaded via a namespace (and not attached):
[1] tools_3.1.1
我也使用此会话信息在另一台机器上得到相同的行为：
> sessionInfo()
R version 3.1.2 (2014-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=C LC_COLLATE=C LC_MONETARY=C LC_MESSAGES=C
[7] LC_PAPER=C LC_NAME=C LC_ADDRESS=C LC_TELEPHONE=C LC_MEASUREMENT=C LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] R6_2.0.1
loaded via a namespace (and not attached):
[1] tools_3.1.2
我的问题如下：
- 我错过了什么还是正常和预期的行为？在那种情况下，为什么会这样？
- 只要我在这里：据我了解，R6 中没有虚拟类和抽象方法的真正实现吗？
编辑：好的，在查看包的源代码后，我意识到，在这一行：
self[[group]][[name]] <- value
group是public_methods, private_methods, public_fields,之一private_fields。所以我猜当一个类被创建时没有任何公共方法，向该类添加一个新的公共方法会失败，因为该组实际上并不存在。