[fpc-devel] Reading empty collection from stream

[Marc Weustink]

Vincent Snijders wrote:
> Hi,
> 
> I am investigating Lazarus issue 7305. The TSynEdit class has a 
> KeyStrokes property of the type TSynEditKeyStrokes, which is a 
> TCollection descendant. The TSynEdit constructor fills the collection 
> with some default items. If I remove the items and stream the TSynEdit, 
> the following line is shown in the lfm:
>     Keystrokes = <>
> 
> If I read this lfm, I don't get a empty KeyStrokes collection, but one 
> filled with the default value.
> 
> I suspect the following lines in TReader.ReadCollection cause this 
> behaviour:
>     if not EndOfList then
>       Collection.Clear;
> 
> Is this a bug or by design? How do I load an empty collection from a 
> stream, if the collection has a default value?

Delphi has the same construction, which is IMO a design flaw.
IMO when a collection is "default" is shouldn't be streamed, so there 
would be nothing written.
I don't know why it is there, since when a "default" collection is 
written, all elements are written. So it never will be <>.

> Note, if I remove the 'Keystrokes = <>' line from the lfm, I will get 
> the default collection too, so I wonder why there are two ways to get 
> the default collection.

I propose to remove the "if not EndOfList then Collection.Clear;" line.



Marc