environment (base)

Environment Access

Description

Get, set, test for and create environments.

Usage

environment(fun = NULL)
environment(fun) <- value
 
is.environment(obj)
 
.GlobalEnv
globalenv()
.BaseNamespaceEnv
 
emptyenv()
baseenv()
 
new.env(hash = FALSE, parent = parent.frame())
 
parent.env(env)
parent.env(env) <- value

Arguments

fun

NULL, which is the default. |

value an environment to associate with the function
obj an arbitrary :R: object.
hash a logical, if TRUE the environment will be hashed
parent

environment created. |

env an environment

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. 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.

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(). The ultimate enclosure of any environment is the empty environment emptyenv(), to which nothing may be assigned. If one follows the parent.env() chain of enclosures back far enough from any environment, eventually one reaches the empty environment.

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.

is.environment is generic: you can write methods to handle specific classes of objects, see InternalMethods.

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 iff obj is an environment.

new.env returns a new (empty) environment enclosed in the parent’s environment, by default.

parent.env returns the parent environment of its argument.

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

See Also

The envir argument of eval, get, and exists.

ls may be used to view the objects in an environment.

Examples

f <- function() "top level function"
 
##-- all three give the same:
environment()
environment(f)
.GlobalEnv
 
ls(envir=environment(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, env=e1)
ls(e1)
ls(e2)
exists("a", env=e2)     # this succeeds by inheritance     
exists("a", env=e2, inherits = FALSE)
exists("+", env=e2)     # this succeeds by inheritance

Wiki discussion

 
rdoc/base/environment.txt · Last modified: 2006/06/12
 
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