Re: Assuaging sour grapes :-) [was: newbie Q: storage management]

["John G. Volan" <johnvolan@sprintmail.com>]

Sorry, I need to make a few clarifications:

John G. Volan wrote:
> 
> Kevin Cline wrote:
> >
> > On most systems, dynamically loaded libraries can be built from C or
> > C++ code.  The library source code is portable, although the commands to build
> > the library from source vary from system to system.
> 
> How is Ada95 different here? Isn't it possible to create DLL's from
> Ada95 source code, too?  (For instance, using Aonix ObjectAda?) And even
> if current implementations of Ada95 don't happen to generate DLLs, isn't
> it at least feasible in principle?

I should have said: "Isn't it feasible in principle using the _current_
definition of Ada95, without need for a language change?"  ObjectAda for
instance supports pragmas Import and Export with Convention=>DLL,
couldn't other compilers just do the same?

I see the portability issue: Without a standard definition of "dynamic
linkage", different implementors could come up with different solutions;
the best we could hope for is for informal agreement between vendors to
support a de-facto standard.

Then there's portability across platforms: Isn't dynamic linkage an
operating-system dependent thing?  Can you take a DLL written in C or
C++ on WindowsNT and port it, and the applications that use it,
immediately to any Unix box?  If so, that's interesting, what would
hinder us from doing the same with Ada95?  On the other hand, if dynamic
linkage mechanisms are OS-specific, how can we possibly invent something
at the language-level that magically gives us portability?

Maybe it's already been done: Consider Java, and Ada95=>JVM compilers
like ObjectAda or AppletMagic. A JVM program isn't "linked" per se;
class files get loaded as they are needed.  However, I don't know
whether a given JVM execution can re-load a different class file to
replace an already-loaded class.

> My question remains: What would "arrays of packages as first- or second-
> class objects" give you?  It seems to me that there's nothing in C or
> C++ that makes it easier to dynamically load different versions of the
> same package/class.  It's still an extra-linguistic mechanism: It
> requires configuration management mechanisms outside the programming
> language level.
> 
> Or am I still missing something...?
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