[fpc-pascal] Clone a instance of object

[Michael Van Canneyt]

On Mon, 23 Sep 2013, Mattias Gaertner wrote:

> On Mon, 23 Sep 2013 11:46:54 +0200 (CEST)
> Michael Van Canneyt <michael at freepascal.org> wrote:
>
>>
>>
>> On Mon, 23 Sep 2013, Zaher Dirkey wrote:
>>
>>>
>>> On Mon, Sep 23, 2013 at 10:02 AM, Michael Van Canneyt <michael at freepascal.org> wrote:
>>>       Var
>>>         C : TBaseObjectClass;
>>>       begin
>>>         C:=TBaseObjectClass(ClassType);
>>>         Result:=C.Create;
>>>       end;
>>>
>>>
>>> ​Yes, that help me, thanks.
>>>
>>> Now about assigning I must repeat it (assign) for every child class copy its field members, is there any trick to copy the values like assigning record var to another record
>>> var?
>>> I know it is kind of strange way :P
>>
>> There is no such safe mechanism.
>
> Well, actually there is a safe mechanism. You use a record to store the
> class variables. But it looks clumsily:
>
> type
> TMyClass = class(TPersistent)
> private
>   type
>     TMyClassVars = record
>       a,b,c: string;
>     end;
> private
>   F: TMyClassVars;
> public
>   procedure Assign(Source: TPersistent);
>   property a: string read F.a write F.a;
> end;
>
> procedure TMyClass.Assign(Source: TPersistent);
> begin
>  F:=TMyClass(Source).F;
>  inherited;
> end;

Yes. But that works only for 'simple' types and still requires you to write code.

For the more general case where you can have arrays, classes, interfaces and whatnot as 
fields of your object, there is simply no correct way.

Michael.