Slots are linked to S4 objects. A slot can be seen as a part, element or a "property" of an object. Say you have a car object, then you can have the slots "price", "number of doors", "type of engine", "mileage".
插槽Slots和S4物件型別相關。一個插槽可以被看作是一個部分，元素，或者物件的某個特性。比如你有一個物件是車，那麼你就有這些插槽：“價格”，“門的數量”，“發動機型別”，“里程數”。 舉例如下： 新建：

setClass("Car",representation=representation(
   price ="numeric",
   numberDoors="numeric",
   typeEngine="character",
   mileage="numeric"))
aCar <-new("Car",price=20000,numberDoors=4,typeEngine
 
="V6",mileage=143)> aCar
Anobject of class"Car"Slot"price":[1]20000Slot"numberDoors":[1]4Slot"typeEngine":[1]"V6"Slot"mileage":[1]143

Here, price, numberDoors, typeEngine and mileage are slots of the S4 class "Car". This is a trivial example, in reality slots themselves can be again complex objects.
訪問：

Slots can be accessed in numerous ways :

> [email protected]
[1]20000> slot(aCar,"typeEngine")[1]"V6"

Slots:The data contained in an objectfrom an S4 classisdefinedby the _slots_ in the class definition.Each slot in an objectis a component of the object; like
      components (that is, elements
 
) of a list, these may be
      extracted andset,using the function‘slot()’or more often
      the operator‘"@"’.However, they differ from list
      components in important ways.First, slots can only be
      referred to by name,notby position,and there isnopartial
      matching of names aswith list elements.

注意：@插槽本身也可以是dataframe，插槽位置用@，之後的dataframe元素用$. 比如：par(bg=x@colors$bg.col,[email protected]$fg.col, xaxs='r',las=2,[email protected]$fg.col)