Why version() ?

[Walter Bright]

Steven Schveighoffer wrote:
> That example has nothing to do with || being allowed, and nothing to do with 
> your exhibit B.  Your simple example makes sense to split into multiple 
> files, but you simply waved your magic "split into multiple files" wand at 
> Hans' code and because of the simplicity of D's versioning system, it's more 
> maintainable?  I find it hard to believe without proof.

I cannot prove to you in any mathematical sort of way. All I can say is 
that I have a lot of experience doing things both ways, and what the 
results are. I can readily believe that it isn't obvious until one has 
done it both ways; programming is full of examples of such. Such as:

#define BEGIN {
#define END }

I can't prove that's a bad idea, either. But experience shows it is <g>.


> Besides, your example exists *without* any new features to the versioning 
> system.  That is, your example just shows how it's easier to maintain if you 
> put the version identifier at the outermost layer, instead of in the 
> innermost layer, and I agree with you there.  I just want to try and get rid 
> of the cruft of:
> 
> version(A)
>    version = AorB;
> version(B)
>    version = AorB;

I think I've been misunderstood here. I never intended one to actually 
use the "or" string in a version, my intent was that one determine just 
what the feature is that is AorB, and name the identifier that. For example:

version (linux)
	version = Pthreads;
version (OSX)
	version = Pthreads;

version (Pthreads)
	...
else version (Windows)
	...

I don't consider that cruft, but very reasonable self-documentation.


> If you want to prove how much easier it is, actually split Hans' rat's nest 
> into multiple files how you would do it, and I'll show you that it isn't any 
> harder to maintain if you use ||.

I already did port it once, many years ago, it's why I know how hard it 
is. Take a look at D's gc which uses personality modules. I ported that 
to the mac pretty easily and never touched the main code. I can't even 
figure out where the mac osx code is in the hbgc or what would need to 
be changed for it. I couldn't even figure out if the hbgc supported OSX 
or not.

To sum up, I've done it both ways. The personality module method 
approach is head and shoulders the clear winner.