[Solved] Enumeration of A TCollection descendant with FOR .. IN

[@nton]

Hi,

I try to enumerate a TCollection descendant with the for .. in statement. The following error occurs:

main.pas(172,10) Error: Incompatible types: got "TCollectionItem" expected "TWBBusinessComponent"

Code: [Select]

var
  ABusComp: TWBBusinessComponent;

//
    for ABusComp in BusinessComponents do  { Error here! }
    begin   

    end

//


Where BusinessComponents is a TWBBusinessComponentCollection with TWBBusinessComponent as items

With the folowing definitions:

Code: [Select]


TWBBusinessComponentCollection = class(TCollection)

TWBBusinessComponent = class(TCollectionItem)


Should I make some special enhancements to the TCollectionItem descendant to make this work?

[Blaazen]

I'm afraid it is impossible this way. For .. in works for strings, sets or generics but TCollection.Items is TFPList.
You will have to use:

Code: [Select]

for i:=0 to Collection.Count-1 do
  with Collection.Items[i] do
    ...

[taazz]

You should change your TWBBusinessComponentCollection. Try to declare the aBusComp as a TCollectionItem and see if that works, if it does, which I presume that it will, then you need to write an enumerator for TWBBussinessComponent and a method in TWBBusinessComponentCollection that will return that enumerator. For an example just take a look on Tcollection.GetEnumerator and TCollectionEnumerator implementation in the classes unit.

[Blaazen]

So for..in loop is more powerful than I expected.
With

Code: [Select]

aBusComp: TCollectionItem; it works. You will only need the casting:

Code: [Select]

for ABusComp in BusinessComponents do 
  with ABusComp as TWBBusinessComponent do
    begin   

    end

[@nton]

Thanks!

It works indeed!

To lose the typecast I should probably override the implementation of IEnumerator and IEnumerable on the TCollection descendant.
(A little too much work for now ...)