[fpc-pascal] Turbo Pascal and Object Pascal ways of OOP
daniel.mantione at freepascal.org
Tue Feb 5 23:33:27 CET 2008
Op Tue, 5 Feb 2008, schreef Marc Weustink:
> Daniël Mantione wrote:
>> Op Tue, 5 Feb 2008, schreef Luiz Americo Pereira Camara:
>>> can i safely use the below object instead of the record and pass directly
>>> to the c function?
>>> TMyObj = object
>>> x: Integer;
>>> y: Integer;
>>> PMyObj = ^TMyObj;
>> Yes, objects (by specification) are defined to have the same binary layout
>> as records.
>>> Moreover, whats the difference between objects and records with methods
>>> (the new Delphi feature)?
>> Objects can have virtual methods, constructors, destructors. The new Delphi
>> feature cannot.
> however with virtuals or constructors/destructors, the memory layout is not
> 100% the same as a record.
A constructor doesn't add a vmtlink. A virtual method does, and a
destructor too because they are virtual. It is never a problem in
practise, because you can declare the virtual method in a descendent,
In the above example, you can perfectly pass a
Tbinary_compatible_obj_with_vmt instance to any C library expecting a
Tbinary_compatible_obj, because the vmtlink is located after the fields
and therefore does not interfere with the binary structure.
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