FPC : RTTI on records - freepascal

Question

This is my first time on this site. Usually, I have no problem to found replies in the old posts but I don't success with my actual problem.
I would like to know how use RTTI functions to know at running time the properties/members of a record under Lazarus/FPC? I know how to do it for a class (Tpersistent descendant and published properties) but not for FPC. Some links indicates how to do it under Delphi (From D2010), but I don't know how to transpose it under Lazarus.
Thanks in advance for help and assistance.
Salim Larhrib.
To kevin : As I told before, this is my first demand. But I understand. You are right. This is my code
procedure TMainForm.btRecordTHashListClick(Sender: TObject);
var
pTData : PTypeData;
pTInfo : PTypeInfo;
TablePtr : PatableRecord;
Loop : Integer;
begin
// Set of Record pointers + HashList
// Create Container
if not Assigned(FTableRecList) then FTableRecList := TFPHashList.Create;
// Insert data
new(TablePtr);
TablePtr^.description := 'Dictionnaire des tables.';
FTableRecList.add('atable', TablePtr );
new(TablePtr);
TablePtr^.description := 'Dictionnaire des fonctions.';
FTableRecList.add('afunction', TablePtr );
new(TablePtr);
TablePtr^.description := 'Dictionnaire des listes d''option.';
FTableRecList.add('alist', TablePtr );
// Read records
for Loop:=0 to FTableRecList.Count-1 do
begin
TablePtr := FTableRecList[Loop];
ShowMessage('Parcours Index : ' + TablePtr^.description);
end;
// Find records
try
TablePtr := FTableRecList.Find('ddafunction');
ShowMessage('Record finded : ' + TablePtr^.description);
except
ShowMessage('Not such record .');
end;
try
TablePtr := FTableRecList.Find('afunction');
ShowMessage('Record finded : ' + TablePtr^.description);
except
ShowMessage('No such record.');
end;
// Free memory : To put later in TFPHashList wrapper
for Loop:=0 to FTableRecList.Count-1 do Dispose(PatableRecord(FTableRecList[Loop]));
// RTTI
pTInfo := TypeInfo(TatableRecord);
pTData := GetTypeData(pTInfo);
ShowMessage('Member count = '+IntToStr(pTData^.PropCount));
end;

Answer 1

WARNING: It works with FPC 2.7.1 or later.
You can deal with record fields using pointers. Here is example:
program rttitest;
uses
TypInfo;
type
TMyRec = record
p1: Integer;
p2: string;
end;
var
td: PTypeData;
ti: PTypeInfo;
mf: PManagedField;
p: Pointer;
f: Pointer;
r: TMyRec;
begin
r.p1 := 312;
r.p2 := 'foo-bar';
ti := TypeInfo(r);
td := GetTypeData(ti);
Writeln(td^.ManagedFldCount); // Get count of record fields
// After ManagedFldCount TTypeData contains list of the TManagedField records
// So ...
p := #(td^.ManagedFldCount); // Point to the ManagedFldCount ...
// Inc(p, SizeOf(Integer)); // Skip it (Wrong for 64-bit targets)
// Next line works for both
Inc(p, SizeOf(td^.ManagedFldCount)); // Skip it
mf := p; // And now in the mf we have data about first record's field
Writeln(mf^.TypeRef^.Name);
Write(r.p1); // Current value
f := #r;
Inc(f, mf^.FldOffset); // Point to the first field
Integer(f^) := 645; // Set field value
Writeln(r.p1); // New value
// Repeat for the second field
Inc(p, SizeOf(TManagedField));
mf := p;
Writeln(mf^.TypeRef^.Name);
Write(r.p2);
f := #r;
Inc(f, mf^.FldOffset);
string(f^) := 'abrakadabra';
Writeln(r.p2);
Readln;
end.