Objectification and Orientedness

[Robert DeBolt]

Hi. I am toying with the implementation of OOPS in PowerBASIC.
I submit the following code for your suggestions and criticisms:

They are patterned after examples in the book "Teach yourself C++"
by Al Stevens.

Rem Ex-07-01.bas
Rem PBCC  4.04.0042

#Compile Exe
#Dim All

#Include "Ex-07-01.inc"

Function PBMain () As Long

	Local lresult As Long
	Local thiscube As Cube

	Constructor(thiscube,7,8,9)
	Volume(thiscube)
	Print "volume = " + Str$(lresult)
	Destructor(thiscube)
	WaitKey$
	
End Function

Rem ---------- a Cube class
Rem Ex-07-01.inc
Rem PBCC  4.04.0042

Macro CLASS=Type

Macro Constructor(mycube, lht,lwd,ldp)
	mycube.m__Cube = CodePtr(Cube__Cube)		' Constructor.
	mycube.m___Cube = CodePtr(Cube___Cube)		' Destructor.
	mycube.m__volume = CodePtr(Cube__volume)	' Volume.
	Call Dword mycube.m__Cube Using Cube__Cube(mycube, lht,lwd,ldp)
End Macro

Macro Destructor(mycube)
	Call Dword mycube.m___Cube Using Cube___Cube(mycube)
End Macro

Macro volume(mycube)
'  Corrected 07-22-08
'   Call Dword thiscube.m__volume Using Cube__volume(thiscube) To lresult
    Call Dword mycube.m__volume Using Cube__volume(mycube) To lresult
End Macro


'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

CLASS Cube
   m_lheight As Long
   m_lwidth  As Long
   m_ldepth As Long
   m__cube As Dword		' Constructor.
   m___cube As Dword		' Destructor.
   m__volume As Dword	' Member function (compute volume).
End CLASS

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

' Constructor.
Sub Cube__Cube(mycube As Cube, lheight As Long, lwidth As Long, ldepth As Long)

	Print "Constructor"
	mycube.m_lheight = lheight
	mycube.m_lwidth  = lwidth
	mycube.m_ldepth  = ldepth

End Sub

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

' Destructor.
Sub Cube___Cube(mycube As Cube)
	Print "Destructor"
End Sub

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

' Member function (compute volume).
Function Cube__volume(mycube As Cube) As Long

	Print "Cube__volume"
	Function = mycube.m_lheight * mycube.m_lwidth * mycube.m_ldepth

End Function

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Edit: 7-22-08 - Changed "thiscube" to "mycube" in the macro "volume(mycube)".

[David L Morris]

Your example workedOK, however, I had hoped for two different results when I tried two cubes?

FUNCTION PBMAIN () AS LONG

    LOCAL lresult AS LONG
    LOCAL thiscube AS Cube
    LOCAL thiscube2 AS Cube

    Constructor(thiscube,7,8,9)
    Constructor(thiscube2,27,28,29)
    Volume(thiscube)
    PRINT "volume = " + STR$(lresult)
    Destructor(thiscube)
    Volume(thiscube2)
    PRINT "volume = " + STR$(lresult)
    Destructor(thiscube2)
    WAITKEY$

END FUNCTION

[Petr Schreiber jr]

Hi,

thanks for sharing this interesting experiment.

I think it is pretty nice, on other side I am not sure if constructor/destructor can remain with the same simple name in case of multiple classes involved.

So maybe it should be Cube__Constructor / Cube__Destructor, or similar according to class it belongs to.


Petr

P.S. Very interesting is that PB editor highlights the CLASS keyword, hmm

[Robert DeBolt]

Thanks, David, for your comment.
I had inadvertantly typed "thiscube" instead of "mycube" in the "volume" macro. The source above has been corrected. Please try again.

I am not sure if constructor/destructor can remain with the same simple name in case of multiple classes involved.

So maybe it should be Cube__Constructor / Cube__Destructor, or similar according to class it belongs to.

P.S. Very interesting is that PB editor highlights the CLASS keyword, hmm

Yes, I agree with you ,Petr. We should have some means to differentiate a cube's volume versus a sphere's volume. However, "Cube__Constructor / Cube__Destructor / Cube_volume" feels to be too much a function call rather than a message. Besides, Cube_volume returns a mysterious value which is hidden from the programmer's view.

I prefer a syntax more like the following:

	Xt.MATTRN(X)		' X'
	XtX.MATMULT(Xt,X)	' X'X
	XtXinv.MATINV(XtX)      ' (X'X)^-1

which may be viewed as "send the MATTRN message to Xt using X."
Or "send the MATMULT message to XtX using Xt and X."

P.S. The Help screen shows that "CLASS" refers to "CLSID$ function" but "CLASS" is not itself a reserved word.