seemsS4Object            package:methods            R Documentation

Heuristic test for an object from an S4 class

Description:

     Returns 'TRUE' if 'object' has been generated from a formally
     defined ('S4') class.  DEPRECATED:  use 'isS4(object)' instead.

Usage:

     seemsS4Object(object)

Arguments:

  object: Any object.

Details:

     The 'class' of the object is examined for the '"package"'
     attribute included when objects are generated from an S4 class. 
     The test in this function has  been superseded by an internal bit
     set when S4 objects are generated.

     The 'seemsS4Object' function is deprecated and will be removed.

     The  test can be fooled in at least two ways:

        1.  It will give 'TRUE' incorrectly if someone puts a
           '"package"' string attribute on the class of an S3 object.
           Presumably unlikely.

        2.  It will give 'FALSE' incorrectly for class definitions and
           certain other objects for packages that have not been
           'INSTALL'ed since the 'seemsS4Object' was added to R. See
           the Warning below.

Value:

     Always 'TRUE' or 'FALSE' for any object.

Warnings:

     One motivation for this function is to prevent standard S3 vector
     operations from being applied to S4 objects that are not vectors.
     Note that 'seemsS4Object()' alone is _not_ that test.  One also
     needs to check that the object does not inherit from class
     '"vector"'.  See the examples.

     The existence of a class definition for the object's class is also
     not equivalent.  S4 class definitions are recorded for S3 classes
     registered via 'setOldClass', but registering does not change the
     class of such objects, so they are not judged to be S4 objects
     (and should not be).

     Certain other S4 objects used to be generated without the
     '"package"' attribute in earlier builds of R, notably class
     definitions.  Packages using S4 objects _must_ be reinstalled with
     a version of R recent enough to contain the 'seemsS4Object'
     function (e.g., R 2.3.0 or later).

Examples:

     ## Not run: ## this is deprecated
     seemsS4Object(1) # FALSE

     seemsS4Object(getClass(class(1)))  #TRUE

     ## how to test for an S4 object that is not a vector

     S4NotVector <-
         function(object) seemsS4Object(object) && !is(object, "vector")

     setClass("classNotNumeric", representation(x="numeric", y="numeric"))

     setClass("classWithNumeric", representation(y="numeric"),
              contains = "numeric")

     obj1 <- new("classNotNumeric", x=1, y=2)

     obj2 <- new("classWithNumeric", 1, y=2)

     seemsS4Object(obj1); seemsS4Object(obj2)  # TRUE, TRUE
     S4NotVector(obj1); S4NotVector(obj2)  # TRUE, FALSE

     removeClass("classNotNumeric")
     removeClass("classWithNumeric")
     ## End(Not run)

