bindenv {base} | R Documentation |
These functions represent an interface for adjustments to environments and bindings within environments. They allow for locking environments as well as individual bindings, and for linking a variable to a function.
lockEnvironment(env, bindings = FALSE) environmentIsLocked(env) lockBinding(sym, env) unlockBinding(sym, env) bindingIsLocked(sym, env) makeActiveBinding(sym, fun, env) bindingIsActive(sym, env)
env |
an environment. |
bindings |
logical specifying whether bindings should be locked. |
sym |
a name object or character string. |
fun |
a function taking zero or one arguments. |
The function lockEnvironment
locks its environment argument,
which must be a normal environment (not base). (Locking the base
environment and namespace may be supported later.) Locking the
environment prevents adding or removing variable bindings from the
environment. Changing the value of a variable is still possible unless
the binding has been locked. The namespace environments of packages
with namespaces are locked when loaded.
lockBinding
locks individual bindings in the specified
environment. The value of a locked binding cannot be changed. Locked
bindings may be removed from an environment unless the environment is
locked.
makeActiveBinding
installs fun
in environment env
so that getting the value of sym
calls fun
with no
arguments, and assigning to sym
calls fun
with one
argument, the value to be assigned. This allows the implementation of
things like C variables linked to R variables and variables linked to
databases, and is used to implement setRefClass
. It may
also be useful for making thread-safe versions of some system globals.
The bindingIsLocked
and environmentIsLocked
return a
length-one logical vector. The remaining functions return
NULL
, invisibly.
Luke Tierney
# locking environments e <- new.env() assign("x", 1, envir = e) get("x", envir = e) lockEnvironment(e) get("x", envir = e) assign("x", 2, envir = e) try(assign("y", 2, envir = e)) # error # locking bindings e <- new.env() assign("x", 1, envir = e) get("x", envir = e) lockBinding("x", e) try(assign("x", 2, envir = e)) # error unlockBinding("x", e) assign("x", 2, envir = e) get("x", envir = e) # active bindings f <- local( { x <- 1 function(v) { if (missing(v)) cat("get\n") else { cat("set\n") x <<- v } x } }) makeActiveBinding("fred", f, .GlobalEnv) bindingIsActive("fred", .GlobalEnv) fred fred <- 2 fred