Using Caché Objects - InterSystems Documentation

Methods
6.6 Instance and Class Methods
Generally, the term “method” refers to an instance method, which is a method that is invoked
from a specific instance of a class that performs some action related to that instance, such as
performing business logic, displaying information about the instance, and so on. For example,
suppose you have an instance of the Sample.Person class (included in the “Samples”
namespace) in memory called MyPerson; you can then invoke its instance methods, such as
its NinetyNine method (a example method that simply returns the value 99):
Set x = MyPerson.NinetyNine()
This line of code uses the NinetyNine method to set x equal to 99.
In addition to instance methods, Caché supports class methods. A class method is not necessarily
associated with a particular object and need not be invoked from an open object. As
such, you can invoke a class method in either of two ways:
• Without any object reference
• From a specific instance in order to act on one or more objects of the class
A class method can refer to other class methods, but cannot refer to any object properties or
instance methods. For example:
Set x = ##class(Invoice).%Open(oid)
Set x = ##class(Patient).%New()
The first example involves the %Open class method of the Invoice class, which takes the
OID of a particular instance, opens that instance, and returns a handle to it; the second
example uses the Patient class' the %New method to create a new Patient instance and return
a handle to it.
Class methods are important because you can invoke them without having an instance that
is already open. For example, you can use the %New and %OpenId class methods to create
or open an instance. Class methods are also useful for actions that involve multiple or all
instances of a class.
6.7 Kinds of Methods
Caché supports four types of methods:
42 Using Caché Objects