[fpc-devel] Suggestion: reference counted objects

[Nikolay Nikolov]

On 09/23/2014 08:47 PM, Boian Mitov wrote:
> This is a valid point.
> The only downside is that the object will every time do a deep copy 
> versus a shallow (pointer only) copy. Deep copy is very, very 
> expensive operation.
> Adding ref. counting to objects is probably equivalent of one 
> interlocked assembly instruction, so a very small difference, probably 
> not even measurable.
> Copy of a large object can take a large memory transfer, and will also 
> reserve memory for each copy, thus significantly increasing memory.
> While both approaches have something going for them, they are not 
> total subside for each other.
Yes, but if you have compiler support for objects with automatic calls 
of constructors/destructor/copy constructor/assignment operator (like in 
C++ classes), and if you also have generics support for objects, you can 
make a generic smart pointer object type that adds reference counting to 
any class. And then the regular class references will serve as weak 
references. Exactly like C++:

http://www.boost.org/doc/libs/1_56_0/libs/smart_ptr/smart_ptr.htm

What's more important is that we can extend objects this way, without 
breaking backward compatibility. But, unfortunately, it's a huge 
slippery slope from there, as anyone, who has dealt with C++ STL error 
messages knows:

http://pascalg.wordpress.com/2008/02/24/stl-error-messages-are-so-great/

Nikolay
> With best regards,
> Boian Mitov
>
> -------------------------------------------------------
> Mitov Software
> www.mitov.com
> -------------------------------------------------------
> *From:* August Oktobar <mailto:augustoktobar at gmail.com>
> *Sent:* Tuesday, September 23, 2014 10:35 AM
> *To:* FPC developers' list <mailto:fpc-devel at lists.freepascal.org>
> *Subject:* Re: [fpc-devel] Suggestion: reference counted objects
> To somebody (probably Sven):
>
> In FPC there is concept of stack based objects (object) that behave 
> like classes (with inheritance)?
> Why not just extend this object with support for constructors and 
> destructors, and there is no need for the ARC?
> On Mon, Sep 22, 2014 at 2:05 PM, Hans-Peter Diettrich 
> <DrDiettrich1 at aol.com <mailto:DrDiettrich1 at aol.com>> wrote:
>
>     Sven Barth schrieb:
>
>         Am 22.09.2014 09:47 schrieb "Michael Schnell"
>         <mschnell at lumino.de <mailto:mschnell at lumino.de>
>
>
>         > Why not use "interface" to add ref-counting to an object ?
>         This seems to work nicely even though the name "interface" in
>         not "speaking" on that behalf.
>
>         Because you'll need to declare an interface for each class you
>         want to have reference counted so that you can access its
>         methods, properties, etc.
>
>
>     This overhead could be eliminated by another syntax extension, like
>       TMyARCclass = interface(TObject)
>     where the Compiler could allow for implementations of the declared
>     methods just as for
>       TMyARCclass = class(TObject)
>     bridging the gap between traditional (strictly declarative)
>     interfaces and classes (including implementations), with or
>     without ARC.
>
>     DoDi
>
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