isS4 {base}

R Documentation

Test for an S4 object

Description

Tests whether the object is an instance of an S4 class.

Usage

isS4(object)

asS4(object, flag = TRUE, complete = TRUE)

Arguments

object	Any R object.
flag	A single logical value; not NA, whether to turn the S4 object flag on or off.
complete	How to complete the transformation to/from S4. Only currently used when flag is FALSE. If 1, the object must convert to a valid S3 object, or an error results. If 2, a non-valid S3 object is left alone, silently. If 0, no conversion is made other than setting the internal bit (used internally but not recommended, since it can result in an invalid object).

Details

Note that isS4 does not rely on the methods package, so in particular it can be used to detect the need to require that package. (But asS4 does depend on methods.)

Note that the S4 methods for primitive functions do not apply to S3 classes and that the methods for basic classes, such as the vector types, are sealed. To apply S4 methods reliably to an S3 object, define an S4 class that extends the S3 class (setOldClass).

When asS4 is called with flag == FALSE, the value of complete controls whether an attempt is made to transform object into a valid object of the implied S3 class. If so, then an object from an S4 class extending an S3 class will be transformed into an S3 object with the corresponding S3 class (see S3Part). This includes classes extending the pseudo-classes array and matrix: such objects will have their class attribute set to NULL.

Value

isS4 always returns TRUE or FALSE according to whether the internal flag marking an S4 object has been turned on for this object.

asS4 will turn this flag on or off, according to argument flag, and in the latter case complete the conversion as described under argument complete. Note that with flag FALSE, an S4 object will not but turned into an S3 object unless there is a valid conversion; that is, an object of type other than "S4" for which the S4 object is an extension, unless argument complete is 0.

See Also

is.object for a more general test; Methods for general information on S4.

Examples

isS4(pi) # FALSE
isS4(getClass("MethodDefinition")) # TRUE

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