Initial value for this variable. This is either a plain value or a function
object. It is normally passed as the 7-th argument of variable->initialise.
Please note that using a normal object (e.g. size(20,5))
causes the same size instances to be shared by all individuals of this
class. In most cases one should use create(size, 20,5) to
force the creation of a new instance. See also class create.
The Prolog class compiler supports this through the following construct:
variable(size, size:=new(size(20,5)), get).
If the argument is a constant, name or int, the variable->alloc_value
is set. Otherwise special precautions are required in
class<-instance
and the variable->init_function
is set.
