[Lazarus] Circular references

[Lance Collins]

Sorry if this is the wrong place to discuss language issues.

I saw the following on the ADUG Delphi list and wondered if there was 
a possible Lazarus feature here.

Cheers
Lance
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 > How can you avoid circular references with two modules that
 > interact with each other?

This has been discussed before in the Delphi newsgroups and it has been
requested of BIBCE (Borland/Inprise/Borland/CodeGear/E9o) several times.
IIRC there may be a QC entry.

Basically it should be possible with a minor language change and not too
much effort from the compiler team. Something like:

unit ParentObject;
interface
TChild = forward class; // My made-up syntax
// or TChild = implementation class; or some other syntax!
TParent = Class
public
   property Child :TChild;
end;
implementation
uses ChildObject;


// Nothing special here, only need the love one-way
// but you could do it both ways if you want
unit ChildObject;
interface
uses ParentObject;
TChild = Class
public
   property Parent :TParent;
end;

"TChild = forward class" tells the compiler that TChild is a class, and the
complete type information is known in the implementation section (which the
compiler can validate). That's all the compiler needs to know in the
interface section - essentially it needs to know the kind and size of the
type. It doesn't require a two-pass compiler or any other extreme make-over.

This feature is often needed and the "if you need to do that then something
is wrong with your design" argument doesn't fly with me. It's one of the C++
features that I wish Delphi had. I'm holding out for D2011 - perhaps the new
compiler will have it!