[fpc-devel] class abstract, class sealed implementation. please review.

[Thaddy]

Florian Klaempfl wrote:
> Vinzent Höfler schrieb:
>   
>> Florian Klaempfl <florian at freepascal.org>:
>>
>>     
>>> Marco van de Voort schrieb:
>>>       
>>>> In our previous episode, Florian Klaempfl said:
>>>>         
>>>>>> This is exactly my point about sealed classes. When you design the
>>>>>> product or class, you have NO way of know what will come in the
>>>>>> future. So you need to stay flexible to change! Yet another OOP
>>>>>> principal that "sealed" tries to prevent!
>>>>>>             
>>>>> This might be true, but what's the difference with private etc.?
>>>>>           
>>>> Private is typically used in nearly every class, sealed in exceptional
>>>> cases. At best.
>>>>         
>>> I meant regarding "flexibility". Declaring a member private makes things
>>> also less flexible.
>>>       
>> The main difference is that "private" restricts visibility, 
>>     
>
> It's not only not visible but neither accessible. And if something is
> not accessible, it affects flexibility.
>
>   
>> whilst "sealed" restricts extensibility. The former is usually a good thing, the latter not.
>>
>>
>> Vinzent.
>>
>>     
>
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>   
There is a strange kind - from an academic point of view - of discussion 
going on here.
- one part is confusing language syntax with compiler optimizations
- another part is driven by not understanding why somebody invented sealed
 classes.
The first is or maybe a side effect.
The second should be understood to be restrictive on purpose, by design. 
I think a lot of people whom I highly regard are focussing in the wrong 
direction. Sealed has a purpose and a very good one: It prevents OO 
extensions by design, which is a good thing. see my example from two 
days ago. And, Marco, this is fully compliant with a true OOP philosofy ;)
just my 2 c