Re: Limited_Controlled and constructor functions

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 19 Jan 2007 14:45:59 +0100, Maciej Sobczak wrote:

> Dmitry A. Kazakov wrote:
>> On Fri, 19 Jan 2007 08:58:54 +0100, Maciej Sobczak wrote:
>> 
>>> What I want to accomplish is the functional way of building lists of 
>>> values of variant types:
>>>
>>> P : constant Params := Make_Params(Param("Hello"),
>>>                                     Param("Ada"),
>>>                                     Param(12),
>>>                                     Param(3.14)));
>> 
>> Hmm, but should the parameters and containers of be limited types?
> 
> Probably not, but...
> 
>> I find it rather natural to be able to copy parameter(s)
> 
> ... I don't like to overengineer things in anticipation of usage 
> patterns that actually might never happen. I prefer to forbid it and 
> wait until it's asked for.

But you used ":=", which was (no matter what RM says (:-)) a primitive
operation undefined for limited types. Prior Ada 2005 it was, now, ":=" in
declarations has a different meaning than in statements...

> In C++ it's two lines of code or even half:
> 
> class MyClass : boost::noncopyable
> ...

Huh, C++ has even weaker means to describe formal types contracts. It has
dire <class T>. In Ada there is limited, tagged, range <> etc. Far too
weak, IMO, but still better than C++.

Anyway, there must be a reason why you wanted to have a compound parameters
object rather than to specify them directly in the factory function. You
didn't say what was the goal. To have an abstract factory? I have a
suspicion that it wouldn't work anyway. BTW, you could try streams and
getting the object directly from the stream instead.

>  > send them over IP...
> 
> Then we're talking about serialization.

Egh, no, serialization is ordering in time. To be able to copy is about
lack of identity and memory-isotropy.

> Limited types don't forbid it.

Limited types is a kludge. There should be a simpler and clearer way to say
that the thingy has no visible compiler-generated copy constructor, no
equality, no aggregates, no assignment (in Ada 95). All these are just
primitive operations or parts of.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de