[fpc-pascal] object model

Michael Van Canneyt michael at freepascal.org
Sat May 29 11:59:22 CEST 2010

On Sat, 29 May 2010, spir ☣ wrote:

> On Sat, 29 May 2010 01:09:50 +0300
> Alberto Narduzzi <albertonarduzzi at yahoo.com> wrote:
>> Hi,
>>> Struct is declared as "class" so it inherits from TObject if not other
>>> class is especified.
>> is that true? I don't mean not to trust you, but is the compiler
>> assuming that, or is it a FPC rule? IMO a class is a class, and doesn't
>> inherit from anything else. Unless specified. BTW, From who does TObject
>> inherit then?
>> Just asking, I never declare anything as a pure class, or if I do I
>> don't care if it descends from TObject or not, actually...
> Hum, there must be a root type, from which all others inherit primitive object mechanics. Such as, and mainly, accessing an attribute. Now, this needs not be obvious on the user-language side, but generally it is. So a test such as anything.isOfType(RootObject) always returns true.
> Don't know about free pascal, but this is very probable (and I assumed it's true before the question was raised).

All classes descent from TObject, always: implicitly or explicitly.

> I take the opportunity to ask about inherited attribute (only methods in FP?) transmission and lookup: there are 2 common schemes:
> * Copy: A subclass holds copies of (references to) inherited methods. So, lookup stops on an object's class.
> * Delegation: A subclass delegates to its superclass when a looked up attribute is not found locally. (The superclass may itself delegate further, this up to the root class.)

Static methods are directly bound by the compiler.
For virtual methods: the actual pointer to the method is in the VMT
A pointer to the VMT  is initialized when an instance is created. 
But I am not sure whether VMTs are linked or whether they are copied for


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