Hidden Features in Delphi related topics (from StackOverflow, until the diamond moderators kill these too)
Posted by jpluimers on 2014/02/20
There are (soon probably “were”) a few very interesting Q&A threads on Stack Overflow in the “Hidden Secrets of” series on Delphi related topics.
I sort of can get (but don’t agree: there is a very good voting system to de-emphasize material that is not useful, but who am I to argue with the minority of “the world is black and white, we just follow the rules” diamondss) that these get closed, but cannot get that very useful material gets deleted for anyone with less than 10-thousand reputation.
- Hidden features in the Delphi language? – Stack Overflow.
- Hidden Features of the Delphi IDE – Stack Overflow.
- delphi – Hidden Features of Oxygene – Stack Overflow.
–jeroen
@Jeroen & David, I’ve deleted my off-topic comments from here. Could you do the same, please ? I’ve also asked moderators to delete my meta question as it seems the users there are not even humans. Never mind. Stack Overflow is not what it was few years ago as I observe. It’s getting worse. Another piece to this mosaic was running the portuguese version of Stack Overflow ideal for cross posting between the sites.
The Wiert Corner - irregular stream of stuff 
Malom said
An observation that I’ve never seen elsewhere is OBJECT (not CLASS) support for interfaces.
Here is a stupid but working example code for that.
unit uObjectInterface;
interface
type
TInterfacedBase = object // Not CLASS
private
FInterfaceTable: Pointer;
FRefCount: Integer;
public
constructor Init;
destructor Done;
function GetInterface: IInterface;
function QueryInterface(const IID: TGUID; out Obj): HResult; stdcall;
function _AddRef: Integer; stdcall;
function _Release: Integer; stdcall;
end;
ITest = interface
function Foo: string;
end;
// TTest = object(ITest) // Must have an ancestor OBJECT type or gives a syntax error
TTest = object(TInterfacedBase, ITest)
public
constructor Init;
function Foo: string;
end;
implementation
uses Windows;
{ TInterfacedBase }
function TInterfacedBase._AddRef: Integer;
begin
Result := InterlockedIncrement(FRefCount);
end;
function TInterfacedBase._Release: Integer;
begin
Result := InterlockedDecrement(FRefCount);
if Result = 0 then
Done;
end;
function TInterfacedBase.QueryInterface(const IID: TGUID; out Obj): HResult;
begin
Result := E_NOINTERFACE;
end;
destructor TInterfacedBase.Done;
begin
// Nothing to do since there was no memory allocation here. It is a stack object.
end;
constructor TInterfacedBase.Init;
const
cInterfaceTable: array[0..2] of Pointer = (
@TInterfacedBase.QueryInterface,
@TInterfacedBase._AddRef,
@TInterfacedBase._Release
);
begin
FInterfaceTable := @cInterfaceTable;
FRefCount := 0;
end;
function TInterfacedBase.GetInterface: IInterface;
begin
Result := IInterface(@FInterfaceTable);
end;
{ TTest }
function TTest.Foo: string;
begin
Result := ‘TTest.Foo’;
end;
procedure ObjectInterfaceTest;
var
TestObj: TTest;
TestIntf: ITest;
S: string;
begin
TestObj.Init;
TestIntf := ITest(TestObj.GetInterface);
S := TestIntf.Foo;
Assert(S = TestObj.Foo);
TestObj.Done;
end;
constructor TTest.Init;
const
cInterfaceTable: array[0..2+1] of Pointer = (
@TInterfacedBase.QueryInterface,
@TInterfacedBase._AddRef,
@TInterfacedBase._Release,
@TTest.Foo
);
begin
FInterfaceTable := @cInterfaceTable;
FRefCount := 0;
end;
initialization
ObjectInterfaceTest;
end.
jpluimers said
Wow, that’s cool!
Mike P said
I am less excited about SO than in the beginning because of how quick moderators are to close questions. I use it less as well.
David M said
Jeroen, I can see it’s closed – but where it is flagged for deletion? I agree deleting would remove a great resource, but when reading the question page I couldn’t see anything about deleting it.
David M said
My bad, I didn’t follow every link. The Hidden features of the IDE question was deleted. I contacted the SO team to ask it be restored. Will follow up here.
jpluimers said
Thanks for contacting SO. I’ve given up on them.
woutervannifterickWouter said
The hidden questions from StackOverflow :)
Hidden features in the Delphi Object Pascal language | The Podcast at Delphi.org said
[…] copy editing. Original question by Johan and others on May 19 2011 at 18:34. Post inspired by Jeroen W. Pluimers’ […]