Why version() ?

[Sean Kelly]

Andrei Alexandrescu wrote:
> Steven Schveighoffer wrote:
>> "Walter Bright" wrote
>> Think of code that is versioned around architecture that would look 
>> horrendous if you have to do version statements that have all 
>> different combinations of stuff.  If I have 5 different architectures 
>> to support, I don't want to have to define a module that has 2^5 
>> different version combinations.  On top of that, the way versioning 
>> works, you need 2^4 * 5 different statements:
>>
>> version(A)
>> {
>>    version = AorB;
>>    version = AorC;
>>    version = AorD;
>>    version = AorE;
>>    version = AorBorC;
>>    version = AorBorD;
>>    // ad nauseum.
>> }
>> version(B)
>> {
>>    // oh fun! let's do it again!!!!
>>    version = AorB;
>>    version = BorC;
>>    version = BorD;
>>    ...
>> }
>>
>> When I add another architecture, *gasp* I have to double the 
>> statements (to do them now with and without version(F) ), and now I 
>> have to do another 2^5 statements for the version(F) block.  Wheee!
> 
> But this is clearly the wrong way of cutting the pie. What you need is 
> define features that are supported by some of the versions. You don't 
> need to judge in terms of logical operators between versions.
> 
> version (A) version = canBeUsedToPickupChicks;
> version (C) version = canBeUsedToPickupChicks;
> // version (B) no good

There's one slightly irritating issue I've run into with versions 
recently.  In the spare few instances where I actually need to do 
something like this, I like to put everything together so I know at a 
glance what's going on.  However, versions may not be defined in class 
scope, so:

class C
{
     version (A) version = useSomeFancyThing;
     version (B) version = useSomeFancyThing;
     version (useSomeFancyThing)
     {
         Fancy[1024] fancyPants;
     }
}

This is illegal.  Kind of a small issue, but I grumbled about it for a 
minute or two before I broken down and just duplicated the declaration 
for each version.  I could have easily put the tests at module scope 
before the class declaration, but I wanted everything together.


Sean