Why version() ?

[Denis Koroskin]

On Tue, 10 Feb 2009 17:14:00 +0300, Don <nospam at nospam.com> wrote:

> Derek Parnell wrote:
>> On Tue, 10 Feb 2009 13:08:03 +0100, Don wrote:
>>
>>> A&&B is not so terrible, since you can do it by nesting, as above.
>>> The big problem is A || B. It creates a mess.
>>  version(A) version = AorB;
>> version(B) version = AorB;
>> version(AorB) {
>>   . . .
>> }
>>
> Yes. And that sucks, because you've got the version statement in two  
> places. And you've had to create an essentially meaningless temporary.  
> [1] Then when you have a more complex expression, especially where A and  
> B appear more than once, it gets disgusting.
>
>
> [1] I know Walter's idea is that you create meaningful identifiers, but  
> in practice this kind of versioning can be a workaround. EG B is  
> "everything except WindowsME".

Version has so many shortcomings that it should definitely be redesigned.

My biggest complaint is that code inside version () {} block should be  
semantically correct. It creates many obstacles and disallows good  
use-cases:
- you cannot mix D1, D2 and (in future) D3 in a single source code file  
without helf of mixins.
- you cannot mix asm for different platforms in one source code file  
(because DMD doesn't understand ARM assembly, for instance)
- etc

Other use-case I came across recently reading .NET Framework source code:

class String :
    IFoo,
    IBar,
    IBaz,
#if SUPPORT_GENERICS
    IComparable<Foo>,
#endif
    IWhee
{
    // *very* large amount of code
}

How would you port it to D without code duplication and meaningless  
intermediate classes?