On Thursday, 20 October 2016 at 09:58:07 UTC, Claude wrote:
I'm digging up that thread, as I want to do some multiple
conditional compilation a well.
Well I'm digging up that thread again, but to post some positive
experience feedback this time as I've found an answer to my own
questions, and I thought I could share them.
I wanted to convert some C preprocessing code to D: thousands of
conditional compilation macros #ifdef, #if defined() used in a
program that determine the capabilities of a platform (number of
CPU cores, SIMD availability, etc). So it had to check compiler
types and versions, combined with the target architecture, and
the OS, and the endianess and so on.
So the C implementation is a stream of:
#if defined(MYOS) || defined(ARCHITECTURE) &&
defined(__weirdstuff)
# define SPECIFIC FEATURE
#else
# blabla
...
And I though I would have to use some || and && operators in my D
code as well.
So I did. I used that trick from Mike Parker and anonymous (see
above in the thread) by declaring "enum bool"s to be checked with
"static if"s later to implement specific feature.
So I had a stream of:
version (Win32)
enum bool WindowsSupported = true;
else
enum bool WindowsSupported = false;
version (Win64)
enum bool WindowsSupported = true; //Ooops
else
enum bool WindowsSupported = false; //Ooops
It turned out to be not so readable (even when using a "string
mixin" to make the code tighter), and I cannot define twice an
enum without using "static if", which was a deal-breaker. Also
the conciseness of the versions for the D compilers (only 4: DMD,
GDC, LDC and SDC), as well as the different OS versions made the
code a lot tighter than the C version.
So I just dropped the enum definition thing and just used
"version" as it was designed to be used:
version (Win32)
version = WindowsSupported;
else version (Win64)
version = WindowsSupported;
else etc...
So to my older question:
* Is there an "idiomatic" or "elegant" way of doing it? Should
we use Mike Parker solution, or use the "template
Version(string name)" solution (which basically just circumvent
"version" specific limitation)?
That little experience showed that using version as it is
designed currently is enough to elegantly cover my needs. And it
seemed to scale well.
Also I think it may force developers to handle all version
specific stuff into one specific module and define your own
version identifiers to list features from compiler, OS, target
architecture version identifiers; which is a good coding practice
anyway.
So:
module mylib.platform;
version (ThisOs)
version = ThatFeature;
else
version = blabla;
etc...
And:
module mylib.feature;
void doFeature()
{
version (ThatFeature)
blabla;
}
But again, that's just my feedback from one single experience
(even though I think that kind of code is quite common in C/C++
cross-platform libraries).
So I'm still curious as why Walter designed "version" that
particular way, and if anyone has bumped on "version"
(quasi-)limitations and what they think about it!
