[fpc-devel] comparing methods

[Mattias Gärtner]

Zitat von Thaddy <thaddy at thaddy.com>:

> Mattias Gärtner wrote:
>> Zitat von Michael Schnell <mschnell at lumino.de>:
>>
>>> Mattias Gärtner wrote:
>>>> Can someone explain why in mode objfpc comparing methods only compares
>>>> the address, but not the instance?
>>>
>>> Seems perfectly logical to me (@ = Address of, in this case "code
>>> address", the code is the same for all instances of a class).
>>
>> OnClick:=@MyClick;
>>
>> The @ operator is more than "address of".
>>
> Nope, it is: although there is some vmt work involved : the data  
> part is for the new instance, not the global instance. Assigning a  
> new method to one of the two instances your example gives makes them  
> unequal because the instances are deep copies or rather new  
> instances of the same class with different addresses. Hopes that  
> helps.

Not at all. But thanks for trying.


> If you assign to an empty variable, like
>
> var a,b:TMyClass;
> begin
> b:= TMyClass.Create;
> a:=b;
> end;
>
> You will get the result you expect.

The 'a,b' above are pointers to mem areas. a=b compares the pointers.
If a,b would be records then a=b would compare the mem.
If a,b would be 'procedure of object' then a=b compares only half of  
the mem. This is different to both cases above.
Hope this helps.

Mattias