Re: Discriminants of tagged types

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Thu, 28 Oct 2010 10:50:51 +0200, Maciej Sobczak  
<see.my.homepage@gmail.com> a écrit:
>> This has nothing to do with copying. Consider a handle of a resource,  
>> e.g.
>> HWND as an example. It is bound to the resource, nevertheless it is
>> copyable.
>
> [...]
> What would it mean to copy a file object? Should the file on disk be
> copied as well? Should the data that is still in the buffer be copied?
> And so on. Instead of answering these questions in an unsatisfactory
> way, it is better to outlaw the dubious operation up front.
Proxy objects needs not to be all the same. At least the Windows API do  
this (as others OS do) : you may open a file multiple times, get multiple  
handles to it, with for each, different access rights. The handle is not  
the file, this is a kind of proxy to a file's physical instance. The  
application on its own side, may do the same with handles, and hide file  
handles behind proxies (two levels). This is even a common construct, as  
in most designs you have references, smart references and proxies allover  
the place.

You obviously have the same with object whose intent is to draw on the  
screen.

May be this is too much wide to be uniquely identified and when the  
concept is referred to, it finally just tell few (and that's what may make  
its exact intent smoggy).

-- 
Si les chats miaulent et font autant de vocalises bizarres, c’est pas pour  
les chiens.