Using object extensions and default functions

BlitzMax Forums/BlitzMax Beginners Area/Using object extensions and default functions

Ryan Burnside

(Posted 2006) [#1]

Ok basically I'm trying to learn how inhearatince works in Bmax.

I have an object that is the base for all my enemy types.

This enemy object has some basic code in it's methods that all the extension objects use. I would like to do something like the following.

type enemy
method update()
(command set)
end method
endtype

this is what I would like to do with an extension object

type red_enemy extends enemy
method update()
(parent command set)
 individual commands
endmethod
endtype

I would like the extension objects to have the parent command data PLUS some small original code added inside those.

H&K	(Posted 2006) [#2]

So were is the problem. Or even a question

What you are doing is ok, but I would call the parent command set from the child command set.

Super.update

Dreamora

(Posted 2006) [#3]

??

If you want to call the parents methods, use super.someMethod (or super.Update() in that case)

all fields / globals / const are automatically present in the extended class as well.

Ryan Burnside

(Posted 2006) [#4]

Well if I put code in the extension object's update command, it doesn't get executed.


Type enemy
Field x#,y#,HP#,speed#,direction#,sprite:TImage
Global enemy_list:TList = New TList
Function Create(x#,y#,speed#,direction#)
	Local temp:enemy = New enemy
	temp.x=x
	temp.y=y
	temp.sprite=enemy_1
	temp.speed = speed
	temp.direction = direction
	enemy_shot.Create(x,y,5,90)
	ListAddLast(enemy_list,temp)
End Function
Method Update()
	x:+Cos(direction)*speed
	y:+Sin(direction)*speed
	' check to see if a shot has hit
	If CollideImage(red_shot,x,y,0,1,0)
		score:+150
		explosion.Create(x,y)
		Destroy()
	EndIf
	' destroy if too tall
		If x<0 or y<0 or x>320 or y> 240
			Destroy()
		EndIf 
	draw_locked_rotated(sprite,x,y,direction,4)
End Method
Method Destroy()
	ListRemove(enemy_list,Self)
	
End Method
EndType


Type small_enemy3 Extends enemy
Function Create(x#,y#,speed#,direction#)
	Local temp:enemy = New enemy
	temp.x=x
	temp.y=y
	temp.sprite=enemy_3
	temp.speed = speed
	temp.direction = direction
	enemy_shot.Create(x,y,5,90)
	ListAddLast(enemy_list,temp)
End Function
Method Update()
	direction:+7
End Method
EndType

H&K	(Posted 2006) [#5]

1) you havent shown us where you are trying to execute it from.

However as a guess a would say that you are using the list to loop through all the enemies and calling the create from there. Im afraid that if that is what you are doing then your problem is that the list doesnt know which ones are enemies and which ones are small enemies.

You need to cast the enemy back to a small enemy. But to know when to do this you need a field in Enemy that is allocated a value to indercate what type each enemy really is.

2) In the create function you are creating an enemy and not a small enemy

deps	(Posted 2006) [#6]

Type small_enemy3 Extends enemy
Function Create(x#,y#,speed#,direction#)
	Local temp:small_enemy3 = New small_enemy3
	temp.x=x
	temp.y=y
	temp.sprite=enemy_3
	temp.speed = speed
	temp.direction = direction
	enemy_shot.Create(x,y,5,90)
	ListAddLast(enemy_list,temp)
End Function
Method Update()
	direction:+7
End Method
EndType

try this

Paposo

(Posted 2006) [#7]

hello Ryan.

H&K and Dreamora talk the correct call to update.

In small_enemy3 you put in update:
Method Update()
super.update()
direction:+7
endmethod

And you call update from instance of small_enemy3

Bye
Paposo

Ryan Burnside

(Posted 2006) [#8]

Thanks I've been away from the game a bit but will try this and get back to you.
Edit: That works great! What is "super"?

Gabriel

(Posted 2006) [#9]

Edit: That works great! What is "super"?

It's an object cast to the type of it's immediate parent type.

IE: If TypeB Extends TypeA then any TypeB can call a TypeA method by casting it to a TypeA. Super does that, only without you necessarily having to know that it's a TypeA in order to make the cast. Does that make sense?

Ryan Burnside

(Posted 2006) [#10]

Yes, I think that is what I was looking for all along thanks.