4.1 Object references

An object reference may be a constant or variable reference to an object.

Constant reference

A constant reference declaration has the form:

name: obj ObjectDescriptor

where name the name of the object and ObjectDescriptor is a description of the object being referred to. The ObjectDescriptor is executed when the data-item is generated as part of the generation of the enclosing object.

An object described by an ObjectDescriptor where the items-part is non-empty – i.e. n >= 1, is called a singular object.

Examples

O1: obj Record
O2: obj Person("John Smith",21)
O3: obj Record
   id: var integer
   owner: ref Person

O1, O2, and O3 are constant objects. O3 is a singular object.

Variable reference

A variable reference declaration has the form:

name: ref object-pattern-name

where name is the name of a reference to an object as described by object-pattern-name, which is the name of a pattern. name may refer different objects during the lifetime of the enclosing object. name is initially none, which means that it does not refer to any object.

Examples

V4: ref Record -- initial value is none
V5: ref Person -- ditto

V4 nd V5 are both variables references.