02: Custom Types Advanced

"The Custom Type is the most powerful feature in Blitz3D Language."

The Custom Type features Dynamic Memory Allocation, Pointer Referencing , and Built-in Double Linked List Management. In this lesson you will learn various ways to access and assign data to Custom Type Variables, Arrays, and Pointers.

The New keyword creates a instance of a Custom Type object which is automatically inserted at the front of the collection. Unlike Globals, Arrays, and Variables you can create new instances during the program's run-time without reserving the memory. This is known as Dynamic Memory Allocation.

When you declare a variable of a Custom Type to store a new instance (ie: myalien.alien = New alien), you are in fact creating a Pointer to the object.

Custom Types Double Linked List Management allow you to use following keywords: Insert, Before, After, First, Last to manipulate the order of objects in the collection sequentially.

Insert myalien Before Last alien

Think Objects!

To enforce the 'object' mindset, I will refer to Custom Types as Objects From this point forward.

Object Definition

Type alien
	Field id%
	Field x#
	Field y#
End Type

Returning an Object Pointer from a Method

Function alienNew.alien()
	this.alien=New alien
	alien_Index=alien_Index+1 ;global counter
	;default values
	Return this
End Function

myalien.alien = alienNew()

Passing an Object Pointer to a Method

Function alienDelete(this.alien)
	Delete this
End Function


Array of Object Pointers

An Array of Object Pointers can be used to randomly access specific object instances.

Dim alien_ID.alien(ALIEN_MAXCOUNT%)



alienposx = alien_ID(1)\x#

myalien.alien = alien_ID(1)

;Alternative Blitz Array
Global alien_ID.alien[ALIEN_MAXCOUNT%]



alienposx = alien_ID[1]\x#

myalien.alien = alien_ID[1]

Array as a Property

Arrays as a Property can be only one dimension and the number of elements must specified with a constant or value, no variables.

Type alienMotherShip
	Field alienstackpointer
	Field alienstack[ALIEN_MAXCOUNT%]
End Type

Function alienmothershipChildPush(this.alienmothership,alienchildID)
End Function

Function alienmothershipChildPop(this.alienmothership)
	Return this\alienstack[this\alienstackpointer]
End Function

Object Pointer as a Property

Object Pointers are null upon creation of the object instance. You have to devise a method of assignment.

Type martian
	Field alien.alien
	Field antennas
End Type

martian1.martian = New martian

martian1\alien.alien = alienNew()


Array of Object Pointers as a Property

Type martianMotherShip
	Field alienstackpointer
	Field alienstack.martian[ALIEN_MAXCOUNT%]
End Type

Function martianmothershipChildPush(this.alienmothership,martian.martian)
End Function

Function martianmothershipChildPop.martian(this.alienmothership)
	Return this\alienstack[this\alienstackpointer]
End Function

Object and Handle Keywords

These two unique Keywords are specifically used with Custom Types. Although these commands are not documented, many Blitz3D Programmers who are aware of them, rely on them to provide random access to individual object instances. I speculate that Blitz3D has its own internal ID Assignment System for objects. The Handle Keyword returns the object's ID. If the ID is assigned to a variable, the Object Keyword will return the Object Pointer from the variable.

handlevar% = Handle(myalien.alien)
myalien.alien = Object.alien(handlevar%)


  1. Using the invader object you created in the Lesson 01, add the following Properties:
    1. Array with 3 Elements: bomb
    2. Object Pointer: parent.invader
    3. Array of Object Pointers with 4 Elements: child.invader
  2. Create an Array of Object Pointers with 64 Elements: invader_ID.

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