r - R中的泛型函数和引用类

Question

我正在阅读Martin Morgan 关于引用类的注释，在幻灯片 7 上，他使用setMethod来定义show函数，而之前没有将其设置为泛型 using setGeneric。

为什么允许这样做？是否有一个方法列表被声明为所有引用类的通用方法，包括show？

Answer 1

show已经是一个通用函数：

> isGeneric("show")
[1] TRUE

可以通过调用获取父环境中的泛型列表getGenerics：

> getGenerics()
An object of class "ObjectsWithPackage":

Object:  "-"    "!="   "["    "*"    "/"    "&"    "%/%"  "%%"   "^"    "+"   
Package: "base" "base" "base" "base" "base" "base" "base" "base" "base" "base"

Object:  "<"    "<="   "=="   ">"    ">="   "|"    "$"    "$<-"  "abs"  "acos"
Package: "base" "base" "base" "base" "base" "base" "base" "base" "base" "base"

Object:  "acosh" "addNextMethod" "Arith" "asin" "asinh" "atan" "atanh" "body<-"
Package: "base"  "methods"       "base"  "base" "base"  "base" "base"  "base"  

Object:  "cbind2"  "ceiling" "coerce"  "coerce<-" "Compare" "Complex" "cos" 
Package: "methods" "base"    "methods" "methods"  "methods" "base"    "base"

Object:  "cosh" "cummax" "cummin" "cumprod" "cumsum" "digamma" "exp"  "expm1"
Package: "base" "base"   "base"   "base"    "base"   "base"    "base" "base" 

Object:  "floor" "gamma" "initialize" "kronecker" "lgamma" "loadMethod" "log" 
Package: "base"  "base"  "methods"    "base"      "base"   "methods"    "base"

Object:  "log10" "log1p" "log2" "Logic" "Math" "Math2"   "Ops"  "rbind2" 
Package: "base"  "base"  "base" "base"  "base" "methods" "base" "methods"

Object:  "round" "show"    "sign" "signif" "sin"  "sinh" "slotsFromS3" "sqrt"
Package: "base"  "methods" "base" "base"   "base" "base" "methods"     "base"

Object:  "Summary" "tan"  "tanh" "trigamma" "trunc"
Package: "base"    "base" "base" "base"     "base" 

Answer 2

如果您查看，?show您会发现有一个默认调度到showDefault. 我似乎记得看到了一个假定可用的其他方法的列表，但我目前找不到它们的链接，所以对于你的第二个问题，我不知道。