R包中的.First.lib习语

Question

我在很多R包中的.First.lib函数中看到以下习语:

fullName <- paste("package", pkgname, sep=":")
myEnv <- as.environment(match(fullName, search()))
barepackage <- sub("([^-]+)_.*", "\\1", pkgname)
dbbase <- file.path(libname, pkgname, "R", barepackage)
rm(.First.lib, envir = myEnv)
lazyLoad(dbbase, myEnv)
if(exists(".First.lib", envir = myEnv, inherits = FALSE)) {
    f <- get(".First.lib", envir = myEnv, inherits = FALSE)
    if(is.function(f))
        f(libname, pkgname)
    else
        stop(gettextf("package '%s' has a non-function '.First.lib'",
                      pkgname),
             domain = NA)
}

我知道在加载包时会运行.First.lib函数.

我知道上面的代码定义了一个包的环境并设置了一个路径,但是我不明白为什么它在显式删除.First.lib函数之后正在寻找一个.First.lib函数.是什么让上述成语如此普遍？将它包含在R包中是"最佳实践"吗？

Answer 1

那种成语很古老.包应该有名称空间并使用.onLoad,.onUnload和.onAttach.例如:

.onLoad <- function(libname, pkgname){
     # do whatever needs to be done when the package is loaded
     # some people use it to bombard users with 
     # messages using 
     packageStartupMessage( "my package is so cool" )
     packageStartupMessage( "so I will print these lines each time you load it")
}

只需将其添加到DESCRIPTION文件中,最好避免调用lazyLoad函数的whold业务:

LazyLoad: true