多層繼承

在 R 中使用 S3 與 R6 的物件導向程式設計

Richie Cotton

Data Evangelist at DataCamp

第 4 章第 3 節：多層繼承.003

第 4 章第 3 節：多層繼承.005

第 4 章第 3 節：多層繼承.006

thing_factory <- R6Class(
  "Thing"
)

child_thing_factory <- R6Class(
  "ChildThing",
  inherit = thing_factory
)

grand_child_thing_factory <- R6Class(
  "GrandChildThing",
  inherit = child_thing_factory
)

thing_factory <- R6Class(
  "Thing",

  public = list(
    do_something = function() {
      message("the parent do_something method")
    }
  )

)

child_thing_factory <- R6Class(
  "ChildThing",
  inherit = thing_factory,

  public = list(
    do_something = function() {
      message("the child do_something method")
    }
  )

)

grand_child_thing_factory <- R6Class(
  "GrandChildThing",
  inherit = child_thing_factory,
  public = list(
    do_something = function() {
      message("the grand-child do_something method")

      super$do_something()

      super$super$do_something()

    }
  )
)

a_grand_child_thing <- grand_child_thing_factory$new()

a_grand_child_thing$do_something()

the grand-child do_something method

the child do_something method

Error in a_grand_child_thing$do_something(): 
  attempt to apply non-function

child_thing_factory <- R6Class(
  "ChildThing",
  inherit = thing_factory,
  public = list(
    do_something = function() {
      message("the child do_something method")
    }
  ),

  active = list(
    super_ = function() super
  )

)

grand_child_thing_factory <- R6Class(
  "GrandChildThing",
  inherit = child_thing_factory,
  public = list(
    do_something = function() {
      message("the grand-child do_something method")

      super$do_something()

      super$super_$do_something()

    }
  )
)

a_grand_child_thing <- grand_child_thing_factory$new()

a_grand_child_thing$do_something()

the grand-child do_something method
the child do_something method
the parent do_something method

重點回顧

R6 物件只能「存取直接父類」
中介類別可以「公開它的父類」
使用名為 super_ 的「主動繫結」
super_ 應直接回傳 super

一起來練習吧！

在 R 中使用 S3 與 R6 的物件導向程式設計