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Help: Problem creating array of objects

BlitzMax Forums/BlitzMax Beginners Area/Help: Problem creating array of objects

Murilo(Posted 2004) [#1]
Strict 

Import "Cell.bmx"

Type Grid

	Local m_aobjGrid:Cell[13, 13]
	
	' Create the grid (instatiate instances of the cell object)
	
	Method New()
	
		For Local y:Byte = 0 To 12
			For Local x:Byte = 0 To 12
				m_aobjGrid[y, x] = New Cell
			Next
		Next

	End method

End Type
When attempting to build the above class, the following line is falling over with a "Syntax error in user defined type declaration":

Local m_aobjGrid:Cell[13, 13]
Am I doing something really stupid here? It is 1:51am and I'm tired, so it wouldn't suprise me...

FYI, here's the contents of the "Cell.bmx" file:

Type Cell

	Field Colour:Byte = 0
	Field State:Byte = 0

End Type
Note: I've stripped out the all of the irrelevant functionality in the above (simplified) classes.

Also, how do I determine the number of elements for multi-dimentioned arrays? I.e. For 2d arrays it's [array].Length.

Many thanks.


Murilo(Posted 2004) [#2]
Sorted it - My "Local" variables need to be "Field" variables.

I didn't want to expose those variables though, as they were internal to the class. Is it possible to prevent these from being visible to instances of the class?


FlameDuck(Posted 2004) [#3]
Is it possible to prevent these from being visible to instances of the class?
No. How would that work, anyway?

If you want class variables then try Global instead of Field.


Murilo(Posted 2004) [#4]
Sorry, I didn't explain it very well (it was late).

I want my variables to be private to the instance of the class and not exposed (member variables?).

In VB.Net:

Public Class Test

Private m_strName As String

    Public Property Name() As String
        Get
            Return m_strName
        End Get
        Set(ByVal Value As String)
            m_strName = Value
        End Set
    End Property

End Class
The m_strName variable is available to all methods/functions in the class but is not exposed to the calling code (i.e. objTest.m_strName is not possible). In VB.Net, I have to use a property (as above) if I want to expose/manipulate the variable "externally".

Is it possible to have private member variables in BlitzMax?


Murilo(Posted 2004) [#5]
How do I use the Public and Private keywords? It looks like "Private" may be what I'm looking for, but I can't get it to work.


xacto(Posted 2004) [#6]
As near as I can tell, Public and Private don't work within a Type. It's a shame because it's difficult to build proper abstractions without them.

Fields are public and open to manipulation by the outside world. The only thing you can do is create a convention for accessing your Type and hope people stick to it.


Murilo(Posted 2004) [#7]
Not being able to have private variables in a class seems to go against the principle of OO to me - I don't want to expose all of my "internal" variables to any instances of the class! Shame.

Thanks though xacto.


Hotcakes(Posted 2004) [#8]
It is possible that perhaps you could create the main Type privately that your functions would use and a Type that extends the main (declared Publicly) with fields you want the user to have access to... I don't think anyone has tried it yet but it's worth looking in to...