r - Rオブジェクトが指定されていない場合の標準ジェネリックメソッドの表示方法

Question

ラスター パッケージで writeRaster 関数を表示しようとしています。

> library("raster")
> writeRaster
standardGeneric for "writeRaster" defined from package "raster"

function (x, filename, ...) 
standardGeneric("writeRaster")

また、showMethods には、getMethod で使用できるオブジェクト名が表示されません。

> showMethods("writeRaster")
Function: writeRaster (package raster)
x="RasterLayer", filename="character"
x="RasterStackBrick", filename="character"

そこからどこへ行くべきか

> getMethod("writeRaster","RasterLayer")

*編集 @Metricsが示唆するように：

> getAnywhere("writeRaster")
A single object matching ‘writeRaster’ was found
It was found in the following places
  package:raster
  namespace:raster
with value

function (x, filename, ...) 
standardGeneric("writeRaster")
<bytecode: 0x5a78b18>
<environment: 0x5acadd8>
attr(,"generic")
[1] "writeRaster"
attr(,"generic")attr(,"package")
[1] "raster"
attr(,"package")
[1] "raster"
attr(,"group")
list()
attr(,"valueClass")
character(0)
attr(,"signature")
[1] "x"        "filename"
attr(,"default")
`\001NULL\001`
attr(,"skeleton")
(function (x, filename, ...) 
stop("invalid call in method dispatch to 'writeRaster' (no default method)", 
    domain = NA))(x, filename, ...)
attr(,"class")
[1] "standardGeneric"
attr(,"class")attr(,"package")
[1] "methods"