init · this · unref

Object Oriented Programming

See Object Oriented Programming in the reference manual.

begintemplate

Syntax:
begintemplate
Description:
Declare a new class or data structure. Any HOC code may appear between the begintemplate and endtemplate declarations. Classes are instantiated with the new statement.

Example:

begintemplate String
public s
strdef s
 proc init() {
   if (numarg()) {
     s = $s1
   }
 }
endtemplate String
objref s
s = new String("Hello")
print s.s

will print “Hello” to the screen.

endtemplate

Syntax:
endtemplate
Description:
Closes the class declaration

See also

begintemplate

objectvar

Syntax:
objectvar
Description:
Synonym for objref.

objref

Syntax:
objref
Description:

A comma separated list declarations of object variables. Object variables are labels (pointers, references) to the actual objects. Thus o1 = o2 merely states that o1 and o2 are labels for the same object. Objects are created with the new statement. When there are no labels for an object the object is deleted. The keywords objectvar and objref are synonyms.

An object has a unique name that can be determined with the print obj statement and consists of the template name followed by an index number in brackets. This name can be used in place of an objref.

Example:

objref vec, g
vec = new Vector(20)
g = new Graph()

creates a vector object and a graph object with pointers named vec and g, respectively.

See also

new, begintemplate, List, Point Processes and Artificial Cells, SectionList

public

Syntax:
public
Description:
A comma separated list of all the names in a class that are available outside the class.

See also

begintemplate

external

Syntax:
external
Description:
A comma separated list of functions, procedures, iterators, objects, strings, or variables defined at the top level that can be executed within this class. This statement is optional but if it exists must follow the begintemplate or public line. This allows an object to get information from the outside and can be used as information shared by all instances. External iterators can only use local variables and arguments.

Example:

global_ra = 100
 func ra_value() {return global_ra}
begintemplate Cell
 external ra_value
 create axon
 proc init() {
    forall Ra = ra_value()  /* just the axon */
 }
endtemplate Cell

execute1() can be used to obtain external information as well.

new

Syntax:
objectvariable = new Object(args)
Description:
Creates a new object/instance of type/class Object and makes objectvariable label/point to it. When the object no longer is pointed to, it no longer exists.

Example:

objref vec
vec = new Vector(30)

creates a vector of size 30 with its pointer named vec.

init()
Syntax:
proc init() { ... }
Description:
If an init procedure is defined in a template, then it is called whenever an instance of the template is created.

See also

new

unref()
Syntax:
proc unref() { print this, " refcount=", $1 }
Description:
If an unref procedure is defined in a template, then it is called whenever the reference count of an object of that type is decremented. The reference count is passed as the argument. When the count is 0, the object will be destroyed on return from unref. This is useful in properly managing objects which mutually reference each other. Note that unref may be called recursively.

NULLobject

Syntax:
objref nil
Description:
When an object variable is first declared, it refers to NULLobject until it has been associated with an instance of some object class by a new statement. A NULLobject object variable can be useful as an argument to certain class methods.

Example:

objref nil
print nil  // prints NULLobject
this
Syntax:
objref this
Description:
Declared inside a template (see begintemplate). Allows the object to call a procedure with itself as one of the arguments.

Example:

begintemplate Demothis
   public printname
   objref this

   proc init() {
     printname()
   }

   proc printname() {
     print "I am ", this
   }
endtemplate Demothis

objref foo[3]
print "at creation"
for i=0,2 foo[i]=new Demothis()
print "check existing"
for i=0,2 foo[i].printname()