| ns-alt {base} | R Documentation |
Alternative interface for specifying a name space within the code of a package.
.Export(...) .Import(...) .ImportFrom(name, ...) .S3method(generic, class, method)
... |
name or literal character string arguments. |
name |
name or literal character string. |
generic |
name or literal character string. |
class |
name or literal character string. |
method |
optional character or function argument. |
As an experimental alternative to using a ‘NAMESPACE’ file it is
possible to add a name space to a package by adding a
Namespace: <package_name> entry to the ‘DESCRIPTION’
file and placing directives to specify imports and exports directly in
package code. These directives should be viewed as declarations, not
as function calls. Except to the optional method argument to
.S3method arguments are not evaluated. These directives should
only be used at top level of package code except as noted below.
.Export is used to declare exports. Its arguments should be
literal names or character strings. .Export should only be
used at package top level.
.Import is used to declare the import of entire name spaces.
Its arguments should be literal names or character strings.
.ImportFrom is used to declare the import of selected
variables from a single name space. The first argument is a literal
name or character string identifying the source name space; the
remaining arguments are literal names or character strings identifying
the variables to import. As an experimental feature both
.Import and .ImportFrom can be used to import
variables into a local environment. The drawback of allowing this
is that dependencies cannot be determined easily at package load
time, and as a result this feature may need to be dropped.
.S3method is used to declare a method for S3-style
UseMethod dispatch. This is needed since methods in packages
that are imported but not on the search path might not be visible to
the standard dispatch mechanism at a call site. The first argument
is the name of the generic, the second specifies the class. The third
argument is optional and defaults to the usual concatenation of
generic and class separated by a period. If supplied, the third
argument should evaluate to a character string or a function. If the
third argument is omitted or a character string is supplied, then a
function by that name must be defined. If a function is supplied,
it is used as the method. When the method is specified as a name,
explicitly or implicitly, the function lookup is handled lazily;
this allows the definition to occur after the .S3method
declaration and also integrates with possible data base storage of
package code.
Luke Tierney
## Not run:
## code for package/name space 'foo'
x <- 1
f <- function(y) c(x,y)
print.foo <- function(x, ...) cat("<a foo>\n")
.Export(f)
S3method(print,foo)
## code for package/name space 'bar'
.Import(foo)
c <- function(...) sum(...)
g <- function(y) f(c(y, 7))
h <- function(y) y+9
.Export(g, h)
## End(Not run)