Re: Standard Ada Preprocessor (Was: why ada is so unpopular ?)

[Marin David Condic <nobody@noplace.com>]

Well, there are things that happen at compile time. Perhaps in theory 
they don't *have* to happen at compile time - but in the world we live 
in and for the forseeable future, things are going to be done at compile 
time.

Since different compilers often support (or don't support) different 
declarations, I'd like some way of saying "If I'm on Gnat - compile this 
declaration - if on Aonix, make this the declaration...". I don't know 
how that can happen at runtime. Likewise, when withing packages that may 
be compiler dependent and using statements from them, I'd like some way 
of doing that and I can't imagine how a procedure call of something that 
doesn't get withed is going to sneak past the compiler and get resolved 
at runtime.

Like I've said elsewhere, perhaps you can handle this through various CM 
and build processes, but often this is harder to manage or it has 
pitfalls organizationally and it doesn't provide a *portable* answer 
that I know I can count on in some other environment. Sure, you can 
create yet one more layer of indirection and hide all that stuff under a 
"portable" interface (and you probably should, even if you had 
conditional compilation) but you've just pushed the problem off one 
level. You've got two separate bodies of code that have to be tracked 
and managed and maintained and you don't necessarily have the tools to 
do that easily, nor is it guaranteed to work if you've got to drag it to 
an as yet to be specified environment.

Conditional compilation is not necessarily pretty, but the whole mess of 
trying to maintain a variety of different targets never is under the 
best of circumstances. Conditional compilation would at least provide a 
portable answer.

MDC


Robert I. Eachus wrote:
> 
> I certainly don't buy the "conditional compilation must happen at 
> compile time" argument.  It may be true in most embedded applications 
> that you can statically know these things at compile time.  But I also 
> deal with creating .dlls that must match the current hardware.  If that 
> means that I have to generate self-modifying code, so be it.  (In 
> practice I build and install the correct dispatch table when 
> initializing a .dll.)

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