get_obj_address {envnames}

Return the memory address of an object

Description

Return the memory address of an object after recursively searching for the object in all the environments defined in a specified environment or in all the environments defined in the whole workspace.

Usage

get_obj_address(
  obj,
  envir = NULL,
  envmap = NULL,
  n = 0,
  include_functions = FALSE
)

Arguments

obj

object whose memory address is requested. It can be given as a variable name or an expression. Strings representing object names are not interpreted and return NULL.

envir

environment where the object should be searched for. All parent environments of envir are searched as well. It defaults to NULL which means that it should be searched in the whole workspace (including packages, namespaces, and user-defined environments).

envmap

data frame containing a lookup table with name-address pairs of environment names and addresses to be used when searching for environment env. It defaults to NULL which means that the lookup table is constructed on the fly with the environments defined in the envir environment –if not NULL–, or in the whole workspace if envir=sNULL. See the details section for more information on its structure.

n

number of levels to go up from the calling function environment to resolve the name of obj. It defaults to 0 which implies the calling environment.

include_functions

whether to include funtion execution environments as environments where the object is searched for. Set this flag to TRUE with caution because there may be several functions where the same object is defined, for instance functions that are called as part of the object searching process!

Details

The object is first searched recursively in all environments defined in the specified environment (if any), by calling obj_find. If no environment is specified, the object is searched recursively in the whole workspace.

The memory address is then retrieved for every object found in those environments having the same name as the given object obj.

Strings return NULL but strings can be the result of an expression passed as argument to this function. In that case, the string is interpreted as an object and its memory address is returned as long as the object exists.

If envmap is passed it should be a data frame providing an address-name pair lookup table of environments and should contain at least the following columns:

• location for user-defined environments, the name of the environment where the environment is located; otherwise NA.

• pathname the full environment path to reach the environment separated by $ (e.g. "env1$env$envx")

• address an 8-digit (32-bit architectures) thru 16-digit (64-bit architectures) memory address of the environment given in pathname enclosed in < > (e.g. "<0000000007DCFB38>" (64-bit architectures)) Be ware that Linux Debian distributions may have a 12-digit memory address representation. So the best way to know is to check a memory address by calling e.g. 'address("x")'.

Passing an envmap lookup table is useful for speedup purposes, in case several calls to this function will be performed in the context of an unchanged set of defined environments. Such envmap data frame can be created by calling get_env_names. Use this parameter with care, as the matrix passed may not correspond to the actual mapping of existing environments to their addresses and in that case results may be different from those expected.

Value

The 8-digit (32-bit architectures) thru 16-digit (64-bit architectures) memory address of the input object given as a string enclosed in <> (e.g. "<0000000005E90988>") (note that Ubuntu Debian may use 12-digit memory addresses), or NULL under any of the following situations:

• the object is NULL, NA, or a string, or any other object whose memory address changes every time the object is referred to (for instance for alist[1] –as opposed to alist[[1]]– where alist is a list.

• the object is a constant (e.g. TRUE, 3, etc.)

• the object does not exist in the given environment.

• the object is an expression that cannot be evaluated in the given environment.

Note that for the last case, although constants have a memory address, this address is meaningless as it changes with every invocation of the function. For instance, running address(3) several times will show a different memory address each time, and that is why get_obj_address returns NULL in those cases.

When envir=NULL (the default) or when an object exists in several environments, the memory address is returned for all of the environments where the object is found. In that case, the addresses are stored in an array whose names attribute shows the environments where the object is found.

Examples

env1 = new.env()
env1$x = 3                       # x defined in environment 'env1'
x = 4                            # x defined in the Global Environment
get_obj_address(env1$x)          # returns the memory address of the object 'x'
                                 # defined in the 'env1' environment
get_obj_address(x, envir=env1)   # same as above
get_obj_address(x)               # Searches for object 'x' everywhere in the workspace and
                                 # returns a named array with the memory address of all its
                                 # occurrences, where the names are the names of the
                                 # environments where x was found.

# Memory addresses of objects whose names are stored in an array and retrieved using sapply()
env1$y <- 2;
objects <- c("x", "y")
sapply(objects, FUN=get_obj_address, envir=env1)	# Note that the address of object "x"
                                                 # is the same as the one returned above
                                                 # by get_obj_address(x, envir=env1)

# Memory address of elements of a list
alist <- list("x")
get_obj_address(alist[[1]])      # memory address of object 'x'
get_obj_address(alist[1])        # NULL because alist[1] has a memory address
                                 # that changes every time alist[1] is referred to.