> On Mar 9, 2018, at 3:55 PM, Michael Van Canneyt <mich...@freepascal.org>
> wrote:
>
> Hence my proposal to 'clean this up’.
A good idea if they would be used. If objects had a couple minor things I
personally could replace some records in certain parts of code and get real
benefits. Someone on the compiler team would actually have to do this work
though so it’s a cost/benefit analysis.
>
>> 3) I suppose it never existed but “override” missing is pretty strange.
>> Historical I guess.
>
> You don't need "overrid"e for objects, it is automatical.
Another mystery of why classes added this then? I personally like it since it’s
an indication of an overriding and gives some compiler warnings.
>
>> 4) Move() on an object copies memory like a record (as a record does, so
>> this is good). Does that mean they laid out in memory just like records?
>
> Yes, although I believe there is a hidden VMT field.
Not sure how they look in memory but that code works so I guess they’re safe to
use as records. I could be wrong though and cause nasty bugs using them as pure
data structors (like passing to C functions!)
type
TDataObject = object
v: array[0..2] of integer;
end;
procedure TestObjectCopy;
var
obj: TDataObject;
data: array[0..2] of integer;
i: integer;
begin
for i := 0 to 2 do
obj.v[i] := 100 + (100 * i);
Move(obj, data, sizeof(TDataObject));
for i := 0 to 2 do
writeln(data[i]);
end;
>
>>
>> So why do we have advanced records then if objects do more than records? The
>> overhead of a virtual method table? Records have a better/cleaner syntax for
>> operator overloads than even classes but what else?
>
> Simple: Delphi compatibility.
>
> You can probably find some of my cries of despair on the mailing lists,
> lamenting the fact that they decided to invent something new when they had
> it all along since many decades :(
I wonder how much code is shared between objects and records in the compiler.
It’s really just a syntax difference if all they really wanted was Delphi
compatibility. It’s a real shame to because the time could have been spent
making objects more unified with classes.
>
>>
>> Unlike C++ the object’s destructor was not called when it went out of scope
>> but if it did that they would be an interesting replacement for classes in
>> some cases. The compiler knows how to cleanup stack variables but does it
>> call any virtual method on objects in this situation?
>
> I do not think so.
Maciej, could you add your management operators to objects? Maybe the code for
records/objects overlaps in places and it could be possible, although, the
operator overload syntax for classes is not the same records (which is really a
shame in itself) so perhaps not.
If you could add that then objects would have built-in ARC and since you can
actually subclass them the implementation would be hidden away (instead of the
messy generic wrapper we need to use with records).
Regards,
Ryan Joseph
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