如何理解slot

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R中的slot该如何翻译，如何理解slot的功能和作用呢，对这不太明白

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关键词：slot 如何理解 slot

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".
Internally, that is represented a list.   
举个例子就是这样的 :
setClass("Car",representation=representation(
   price = "numeric",
   numberDoors="numeric",
   typeEngine="character",
   mileage="numeric"
))
aCar <- new("Car",price=20000,numberDoors=4,typeEngine="V6",mileage=143)

> aCar
An object of class "Car"
Slot "price":
[1] 20000

Slot "numberDoors":
[1] 4

Slot "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.
  
Slots can be accessed in numerous ways :
> aCar@price
[1] 20000
> slot(aCar,"typeEngine")
[1] "V6"

这里有特别详细的说明文档：
http://stackoverflow.com/questions/4713968/r-what-are-slots
http://stat.ethz.ch/R-manual/R-devel/library/methods/html/slot.html
https://stat.ethz.ch/R-manual/R-devel/library/base/html/slotOp.html

比如:
setClass("track", representation(x="numeric", y="numeric"))
myTrack <- new("track", x = -4:4, y = exp(-4:4))
slot(myTrack, "x")
slot(myTrack, "y") <- log(slot(myTrack, "y"))
utils::str(myTrack)

getSlots("track") # or
getSlots(getClass("track"))
slotNames(class(myTrack)) # is the same as
slotNames(myTrack)