Question I’ve always had. Why do I need to cast “value” to “pointer" otherwise I get: Incompatible types: got "Pointer" expected “TObject” error?. I don’t find this very helpful and it doesn’t really make sense even.

var
  list: TObjectList;
  value: TObject;
begin
  for pointer(value) in list do
    ;

Regards,
Ryan Joseph

Well, TObjectList is a descendant of TList, which is of course a non-generic list of void pointers. The enumerator for TList that allows the for-in loop to work, called TListEnumerator, as such obviously implements GetCurrent as returning "pointer".

TObjectList doesn't have its own enumerator implementation on top of the TList one or anything like that, so when you use for-in on TObjectList, you're using the pointer-based TList one.

The fix for this is simple IMO: use a generic list class instead. For example, if you want something that works exactly like your code example, you can specialize TObjectList from Generics.Collections literally *with* TObject:

type
  TBaseObjectList = TObjectList<TObject>;
var
  list: TBaseObjectList;
  value: TObject;
begin
  for pointer(value) in list do
    ;

Ryan Joseph schrieb am Do., 26. Sep. 2019, 17:37:

Aside from what Ben wrote I wonder whether such a cast should be able to compile at all... 🤔

And we should probably add a proper TObject enumerator to TObjectList.

Regards,
Sven

AM Ben Grasset wrote

-snip-

I meant to change the last part of the revised code example to:

  for value in list do

because obviously the pointer cast is no longer necessary in that case.

On Sep 26, 2019, at 1:34 PM, Sven Barth via fpc-pascal wrote: And we should probably add a proper TObject enumerator to TObjectList.

I just assumed that had to be there! I’ll make a generic replacement like Ben suggests.

Regards,
Ryan Joseph