Tutorial using the GC with C++ objects

[codifiesParticipant]

http://bedroomcoders.co.uk/monkey-2-wrapping-c-classes/

in case anyone is wondering I write these as much for myself as anyone else, writing up new things I’ve learnt helps me properly grok what is going on and also adds as my own reference – if it is also useful for someone else occasionally, then that make me happy.

[Mark SiblyKeymaster]

Very nice, however one important issue that I should have picked up on earlier…

MXRectangle should be declared as a class not a struct, eg:

Monkey

Extern Class MXRectangle 'Note: No 'Extends Void' - this is a REAL mx2 object! Method New( w:Int,h:Int ) End Public Function Main() Local r:=New MXRectangle( 10,20 ) 'easy! End

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Extern   Class MXRectangle    'Note: No 'Extends Void' - this is a REAL mx2 object!    Method New( w:Int,h:Int ) End   Public   Function Main()    Local r:=New MXRectangle( 10,20 )   'easy! End

The problem with using a Struct Ptr is that GC does not track pointers – only class references (which, yes, are really pointers in C++, but you know what I mean…) – so assigning a ptr to a variable will NOT keep an object alive.

This in fact makes things easier though, as there is no need to use a factory method or bbGCNew() on the C++ side (you still can but you need to be a bit careful – more on this later) and there’s no need to have ‘Ptr’ everywhere in the mx2 code since it’s a real mx2 object.

Sorry about not making that clear earlier, I wasn’t look at all the code!

[codifiesParticipant]

lol just as well i’m having dns issues….

I’ll correct it, thanks

 

websites off line for a bit – sleeeeeeep (please )

new changes really made things a lot easier, now a proper 1st class citizen, with c++ methods called from the mx2 class wonderful!

[codifiesParticipant]

gah just when I thought I had it all,

if I try to extend MXRectangle (in MX2 code) (so I can add extra code to some of the methods) its asking for the default constructor of MXRectangle ?

I have callbacks (from C++ to MX2) working but then that would mean ctor / del callbacks and a callback for any method I wanted to intercept – doable but cumbersom

for example if I want each instance to keep a list of children to protect them from the GC (while the parent is still alive) ….

JNI (in Java) , Lua etc have a bunch of C routines to create language objects another way round would be if I could create a List<T> in C code without having to cope with all the MX2 name massaging (its not quite as bad as mangling!) but then that would probably be a bunch of work for something maybe not many people would use ??

[Mark SiblyKeymaster]

if I try to extend MXRectangle (in MX2 code) (so I can add extra code to some of the methods) its asking for the default constructor of MXRectangle ?

This is just normal OO behaviour. You can either added a default ctor to MXRectangle, or use Super.New(…) in dervided class ctors.

[codifiesParticipant]

I’m not sure what you mean, as Super.New(..  also doesn’t compile

I can’t see any way to extend an extern class at all

[codifiesParticipant]

Monkey

Extern class RectMX="RectangleMX" Method area:Float()="Area" ' order unimportant field height:Float="Height" Method New( w:float,h:float ) Field width:Float="Width" End Public Class exRectMX Extends RectMX method New(w:Float, h:Float) Super.New(w,h) End End

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Extern   class RectMX="RectangleMX" Method area:Float()="Area"    ' order unimportant field height:Float="Height" Method New( w:float,h:float ) Field width:Float="Width" End Public   Class exRectMX Extends RectMX method New(w:Float, h:Float) Super.New(w,h) End End

won’t compile for example

[codifiesParticipant]

Monkey

RectangleMX::RectangleMX():Rectangle(0,0)

1	RectangleMX::RectangleMX():Rectangle(0,0)

got it!

but what I don’t quite follow, if this never gets executed (and it doesn’t) why is it needed ?

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