| # File src/library/base/R/userhooks.R |
| # Part of the R package, https://www.R-project.org |
| # |
| # Copyright (C) 1995-2015 The R Core Team |
| # |
| # This program is free software; you can redistribute it and/or modify |
| # it under the terms of the GNU General Public License as published by |
| # the Free Software Foundation; either version 2 of the License, or |
| # (at your option) any later version. |
| # |
| # This program is distributed in the hope that it will be useful, |
| # but WITHOUT ANY WARRANTY; without even the implied warranty of |
| # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| # GNU General Public License for more details. |
| # |
| # A copy of the GNU General Public License is available at |
| # https://www.R-project.org/Licenses/ |
| |
| ## presumed small |
| .userHooksEnv <- new.env(hash = FALSE, parent = baseenv()) |
| |
| packageEvent <- |
| function(pkgname, event=c("onLoad", "attach", "detach", "onUnload")) |
| { |
| event <- match.arg(event) |
| pkgname <- strsplit(pkgname, "_", fixed=TRUE)[[1L]][1L] |
| paste("UserHook", pkgname, event, sep = "::") |
| } |
| |
| getHook <- function(hookName) |
| get0(hookName, envir = .userHooksEnv, inherits = FALSE, ifnotfound = list()) |
| |
| setHook <- function(hookName, value, |
| action = c("append", "prepend", "replace")) |
| { |
| action <- match.arg(action) |
| old <- getHook(hookName) |
| new <- switch(action, |
| "append" = c(old, value), |
| "prepend" = c(value, old), |
| "replace" = if (is.null(value) || is.list(value)) value else list(value)) |
| if (length(new)) |
| assign(hookName, new, envir = .userHooksEnv, inherits = FALSE) |
| else if(exists(hookName, envir = .userHooksEnv, inherits = FALSE)) |
| remove(list=hookName, envir = .userHooksEnv, inherits = FALSE) |
| invisible() |
| } |