On Tuesday, 30 June 2015 at 16:19:56 UTC, Jonathan M Davis wrote:
On Tuesday, 30 June 2015 at 15:55:49 UTC, bitwise wrote:
On Tuesday, 30 June 2015 at 02:30:44 UTC, Walter Bright wrote:
I don't believe a macro processor is necessary to write
systems code, nor do I believe version expressions are,
either.
Waiiit a minute...reading this again, it seems you are talking
about writing code for a single system.
In that case, yea, I suppose you can get by without versions.
The market in multi-platform mobile apps is not something that
should be ignored though.
You need version blocks to distinguish between platforms (be it
OSes or architectures or whatever), but code like that should
be wrapped at a fairly low level, and most code shouldn't have
anything like that in it. e.g. druntime has tons of version
blocks, whereas Phobos has relatively few. Certainly, in
general, if you're using complex expressions for versions, you
should probably be rethinking how you're doing your code. I've
dealt with code before that shared code across multiple
products and altered its behavior via ifdefs, and it was a
_disaster_. It would have been _far_ cleaner to just separate
it out via libraries and section off the system-specific code
such that it was contained and generally small. Once in a
while, being able to && or || version identifiers like linux
and FreeBSD would be nice, but on the whole, I have to agree
that if you're doing much of that, it's just a recipe for
disaster. I suppose that the problem is that it's just useful
enough in some cases that it's annoying not to have it, but if
we _did_ have it, it would be abused like there's no tomorrow.
For a concrete example from my experience, take a massively
multi-platform codebase like Chromium, which is littered with
#ifdef logic like this, ie #if defined(OS_CHROMEOS) ||
defined(OS_WIN) || defined(OS_LINUX):
http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/about_flags.cc?r1=279969&r2=279970&;
It would be better if that logic weren't spread out everywhere
and was abstracted out into a single place, replaced by a more
specific named feature, as they've attempted to do a little here:
http://src.chromium.org/viewvc/chrome/trunk/src/build/build_config.h
Specifically, they can simply use USE_TCMALLOC instead of #if
(defined(OS_WIN) || defined(OS_LINUX) || defined(OS_ANDROID)) &&
!defined(NO_TCMALLOC) everywhere in the source.
Yes, that means you sometimes need to check build_config.h to see
how USE_TCMALLOC is defined when reading those other files,
rather than always having the logic on hand. That's the
trade-off, I think it's worth it.
I believe Walter is simply trying to enforce such centralization
of version logic, and I agree with him.
