| bindenv | 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) activeBindingFunction(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.
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.
Currently active bindings are not preserved during package installation,
but they can be created in .onLoad.
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
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