base (version 3.5.0)

environment: Environment Access

Description

Get, set, test for and create environments.

Usage

environment(fun = NULL)
environment(fun) <- value
is.environment(x)
.GlobalEnv
globalenv()
.BaseNamespaceEnv
emptyenv()
baseenv()
new.env(hash = TRUE, parent = parent.frame(), size = 29L)
parent.env(env)
parent.env(env) <- value
environmentName(env)
env.profile(env)

Arguments

fun

a function, a formula, or NULL, which is the default.

value

an environment to associate with the function

x

an arbitrary R object.

hash

a logical, if TRUE the environment will use a hash table.

parent

an environment to be used as the enclosure of the environment created.

env

an environment

size

an integer specifying the initial size for a hashed environment. An internal default value will be used if size is NA or zero. This argument is ignored if hash is FALSE.

Value

If fun is a function or a formula then environment(fun) returns the environment associated with that function or formula. If fun is NULL then the current evaluation environment is returned.

The replacement form sets the environment of the function or formula fun to the value given.

is.environment(obj) returns TRUE if and only if obj is an environment.

new.env returns a new (empty) environment with (by default) enclosure the parent frame.

parent.env returns the enclosing environment of its argument.

parent.env<- sets the enclosing environment of its first argument.

environmentName returns a character string, that given when the environment is printed or "" if it is not a named environment.

env.profile returns a list with the following components: size the number of chains that can be stored in the hash table, nchains the number of non-empty chains in the table (as reported by HASHPRI), and counts an integer vector giving the length of each chain (zero for empty chains). This function is intended to assess the performance of hashed environments. When env is a non-hashed environment, NULL is returned.

Details

Environments consist of a frame, or collection of named objects, and a pointer to an enclosing environment. The most common example is the frame of variables local to a function call; its enclosure is the environment where the function was defined (unless changed subsequently). The enclosing environment is distinguished from the parent frame: the latter (returned by parent.frame) refers to the environment of the caller of a function. Since confusion is so easy, it is best never to use ‘parent’ in connection with an environment (despite the presence of the function parent.env).

When get or exists search an environment with the default inherits = TRUE, they look for the variable in the frame, then in the enclosing frame, and so on.

The global environment .GlobalEnv, more often known as the user's workspace, is the first item on the search path. It can also be accessed by globalenv(). On the search path, each item's enclosure is the next item.

The object .BaseNamespaceEnv is the namespace environment for the base package. The environment of the base package itself is available as baseenv().

If one follows the chain of enclosures found by repeatedly calling parent.env from any environment, eventually one reaches the empty environment emptyenv(), into which nothing may be assigned.

The replacement function parent.env<- is extremely dangerous as it can be used to destructively change environments in ways that violate assumptions made by the internal C code. It may be removed in the near future.

The replacement form of environment, is.environment, baseenv, emptyenv and globalenv are primitive functions.

System environments, such as the base, global and empty environments, have names as do the package and namespace environments and those generated by attach(). Other environments can be named by giving a "name" attribute, but this needs to be done with care as environments have unusual copying semantics.

See Also

For the performance implications of hashing or not, see https://en.wikipedia.org/wiki/Hash_table.

The envir argument of eval, get, and exists.

ls may be used to view the objects in an environment, and hence ls.str may be useful for an overview.

sys.source can be used to populate an environment.

Examples

# NOT RUN {
f <- function() "top level function"

##-- all three give the same:
environment()
environment(f)
.GlobalEnv

ls(envir = environment(stats::approxfun(1:2, 1:2, method = "const")))

is.environment(.GlobalEnv) # TRUE

e1 <- new.env(parent = baseenv())  # this one has enclosure package:base.
e2 <- new.env(parent = e1)
assign("a", 3, envir = e1)
ls(e1)
ls(e2)
exists("a", envir = e2)   # this succeeds by inheritance
exists("a", envir = e2, inherits = FALSE)
exists("+", envir = e2)   # this succeeds by inheritance

eh <- new.env(hash = TRUE, size = NA)
with(env.profile(eh), stopifnot(size == length(counts)))
# }