D.2 引用

get(x, pos = -1, envir = as.environment(pos), mode = "any",
    inherits = TRUE)

mget(x, envir = as.environment(-1), mode = "any", ifnotfound,
     inherits = FALSE)

dynGet(x, ifnotfound = , minframe = 1L, inherits = FALSE)
get Return the Value of a Named Object

exists Is an Object Defined?

exists(x, where = -1, envir = , frame, mode = "any",
       inherits = TRUE)

get0(x, envir = pos.to.env(-1L), mode = "any", inherits = TRUE,
     ifnotfound = NULL)