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ID: 8003
Created on: February 6, 2001 06:36
Updated on: April 22, 2010 21:31

How to make a collection property of VFP object
After some investigation, I managed to make a collection-like property of object. The following is a simple sample of how to organize collection-like access (rough, need to improve it to work as real collection). It is just to show an approach.

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Created by: 
Vlad Grynchyshyn
Soft Serve
Lviv

DEFINE CLASS coll AS custom
	Name = "coll"
	DIMENSION a[1]
	PROCEDURE a_access
		LPARAMETERS m.nIndex1
		do case
			case vartype(m.nIndex1) == 'N'
				return THIS.a[m.nIndex1]
			case vartype(m.nIndex1) == 'C'
				return THIS.a[1]
			case vartype(m.nIndex1) == 'L'
				return THIS
		endcase
		*To do: Modify this routine for the Access method
	ENDPROC

	PROCEDURE a_assign
		LPARAMETERS vNewVal, m.nIndex1
		do case
			case vartype(m.nIndex1) == 'N'
				THIS.a[m.nIndex1] = m.vNewVal
			case vartype(m.nIndex1) == 'C'
				THIS.a[1] = m.vNewVal
			case ISNULL(m.nIndex1)
				THIS.a[1] = m.vNewVal
		endcase
	ENDPROC
ENDDEFINE
Now, the following are the test commands:

oo = createobject("coll")
oo.a(1) = 5 && no error
? oo.a(1) && displays 5
? oo.a("qweqwe") && displays 5 anyway!
? oo.a.class && displays 'Coll'
? oo.a && displays 5
oo.a("qweqwe") = 1 && no error
? oo.a(1) && displays 1
oo.a.tag = '2'
? oo.a.tag && displays 2
&& Now, the main trick - allow to access objects in collection
oo.a(1) = createobject('coll')
? oo.a("qwe").class && displays 'Coll'
oo.a("qwe").a(1) = 5 && no error
? oo.a("qwe").a(1) && displays 5!

Using above approach, it is easy to make a collection property in VFP. In detail - Access method allows to access array property as object when you return object reference from the Access method. This is very significant feature that allows to organize such collection-wide methods as "Collection.Add('item')" or 'Collection.Count' or 'Cllection.Items(index)'. Guess these functions will handle some object that is not accessible from outside world by normal means, for example, restricted in this_Access method.

I hope I will enhance this idea and make a generic collection class.

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