Methods to Initialize New Objects from a Class
The arguments to function
new to create an object from a
particular class can be interpreted specially for that class, by the
definition of a method for function
initialize for the class.
This documentation describes some existing methods, and also outlines
how to write new ones.
signature(.Object = "ANY")
The default method for
initializetakes either named or unnamed arguments. Argument names must be the names of slots in this class definition, and the corresponding arguments must be valid objects for the slot (that is, have the same class as specified for the slot, or some superclass of that class). If the object comes from a superclass, it is not coerced strictly, so normally it will retain its current class (specifically,
as(object, Class, strict = FALSE)).
Unnamed arguments must be objects of this class, of one of its superclasses, or one of its subclasses (from the class, from a class this class extends, or from a class that extends this class). If the object is from a superclass, this normally defines some of the slots in the object. If the object is from a subclass, the new object is that argument, coerced to the current class.
Unnamed arguments are processed first, in the order they appear. Then named arguments are processed. Therefore, explicit values for slots always override any values inferred from superclass or subclass arguments.
signature(.Object = "traceable")
Objects of a class that extends
traceableare used to implement debug tracing (see class traceable and
initializemethod for these classes takes special arguments
def, tracer, exit, at, print. The first of these is the object to use as the original definition (e.g., a function). The others correspond to the arguments to
signature(.Object = "environment"),
signature(.Object = ".environment")
initializemethod for environments takes a named list of objects to be used to initialize the environment. Subclasses of
"environment"inherit an initialize method through
".environment", which has the additional effect of allocating a new environment. If you define your own method for such a subclass, be sure either to call the existing method via
callNextMethodor allocate an environment in your method, since environments are references and are not duplicated automatically.
signature(.Object = "signature")
This is a method for internal use only. It takes an optional
functionDefargument to provide a generic function with a
signatureslot to define the argument names. See Methods_Details for details.
Writing Initialization Methods
Initialization methods provide a general mechanism corresponding to generator functions in other languages.
The arguments to
.... Nearly always,
initialize is called from
not directly. The
.Object argument is then the
prototype object from the class.
Two techniques are often appropriate for
special argument names and
You may want argument names that are more natural to your users than
the (default) slot names. These will be the formal arguments to
your method definition, in addition to
.Object (always) and
... (optionally). For example, the method for class
"traceable" documented above would be created by a call to
setMethod of the form:
1 2 3
In this example, no other arguments are meaningful, and the resulting method will throw an error if other names are supplied.
When your new class extends another class, you may want to call the
initialize method for this superclass (either a special method or the
default). For example, suppose you want to define a method for your
class, with special argument
x, but you also want users to be
able to set slots specifically. If you want
x to override the
slot information, the beginning of your method definition might look
something like this:
1 2 3
You could also choose to have the inherited method override, by first
x, and then calling the next method.
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