OR in version conditional compilation

[jxel]

On Friday, 20 March 2020 at 21:03:55 UTC, Jonathan M Davis wrote:
> On Wednesday, March 18, 2020 10:23:26 AM MDT IGotD- via 
> Digitalmars-d-learn wrote:
>> I have not seen any example where version has several OR 
>> matches.
>>
>> Example idiom:
>>
>> version(X86_64 || X86)
>> {
>>
>> }
>> else version(ARM || Thumb)
>> {
>>
>> }...
>>
>> you get the idea. So is this possible at all or do you have to 
>> duplicate the code for each version identifier despite they 
>> are equal for many version identifiers?
>
> To add to what the others have said, the reasons that Walter is 
> against having boolean conditions in version statements have to 
> do with how using boolean conditions in #ifdefs in C/C++ has 
> historically been a big source of bugs. So, disallowing it 
> helps prevent certain classes of bugs. It's why druntime 
> duplicates most C declarations across platforms.

What kind of bugs are those?

> In general, I think that Walter's approach here is probably the 
> right one, but it can certainly be annoying in cases where you 
> have to duplicate code that actually is the same rather than 
> being subtly different, and a lot of people dislike it enough 
> that they use workarounds like those discussed in this thread.


Sadly it still shares probably the worst bug with the C preposser 
in that anything that isnt defined simply evaluates to false. If 
you have a typo then the code will still "work". His approach 
only works if you can put an assert in the else branch. Which is 
the case for C/C++ as well. That isnt always possible, as a 
result you still have the same problem with typos.

> And of course, some of the same bugs that come up with #ifdefs 
> come up with static ifs in generic code (particularly with 
> range-based code that changes what it's doing based on arange's 
> type), but at least those can be found with thorough tests on a 
> single platform, whereas version-related bugs tend to require 
> that you run thorough tests on each platform.
>
> - Jonathan M Davis

You still need to test your code on those platforms, so if you 
are supporting them you still have related problems.