[fpc-devel] Published record

[Michael Van Canneyt]

On Sat, 17 Aug 2024, Michalis Kamburelis wrote:

> Thanks Michael!
>
> OK, that's partially good news :)
>
> I understand that streaming records by default to LFM would lead to
> too many questions (and I'm unsure whether Delphi does it too, for
> records and DFM).

It does not. 
Streaming has not changed in an essential way since  D7, I think.

With the coming of extended rtti, they could have changed it, but they
didn't, I believe since it would be difficult to maintain backwards
compatibility.

> If this means they are not allowed in the
> "published" section, *but* the RTTI is capable of telling me what
> records are in the "public" section, and read / write them (using
> proper getters / setters), this is something we can work with.

You should be fine then, as this is supported.

>
> I mean, I can 1. add my own serialization / deserialization of them,
> and 2. make them exposed in the object inspector in CGE editor.
>
> (
> Details:
> AD 1 - For serialization / deserialization, in Castle Game Engine, we
> use CastleComponentSerialize on top of FpJsonRtti. One of the reasons
> I like JSON and FpJsonRtti over LFM is that this gives us more control
> -- I know I can add code to CastleComponentSerialize to deal with
> records, if only RTTI tells me about them.

I prefer JSON too.

> AD 2 - For object inspector, we use Lazarus "ObjectInspector" unit.
> I'm less sure about it, but hopefully it is possible to add there
> "fake" subcomponents too.
> )

Actually, it is!

see the work the FP/Lazarus foundation sponsored in

lazarus/components/jitclasses/

>
> Can you expand your statement "It is since some time, but you must
> explicitly enable it."? What compiler switch enables it? What API
> should I use to access it -- Rtti unit in FPC has all we need? (I
> guess TypeInfo unit API does not expose it, or it does?)
>
> To make my question more concrete, imagine a code like this:
>
> """
> type
>  TVector3 = record X, Y, Z: Single end;
>  TCastleTransform = class
>  public
>    property Translation: TVector3 read ... write ...;
>    property Scale: TVector3 read ... write ...;
>  end;
> """
>
> I'm looking for a way to tell, at runtime, using RTTI, having any
> instance of TObject (maybe of TCastleTransform):
>
> - what public properties of type TVector3 are there (like
> "Translation" and "Scale"),
> - what public fields does TVector3 have (like X, Y, Z) (this is
> nice-to-have, we could work without this info but then limiting our
> record serialization / deserialization to only specific record types),
> - read / write these record properties using the proper getter /
> setter (whether it's direct field access or a method).

This is all perfectly possible.

Simply add

   {$RTTI EXPLICIT
      PROPERTIES([vcPublic])
      FIELDS([vcPublic])
      METHODS([vcPublic])}

in your units and you're all set.

Michael.