Why version() ?

[Walter Bright]

Nick Sabalausky wrote:
> I have to admit, that's a very compelling example. I hadn't thought of 
> anything like that.

I didn't either, until I got bit by it <g>.


> I guess the moral is "DRY is normally great, but be very 
> careful with it when using it across multiple builds." But I'm still not 
> sure we should be going that far. For instance:
> 
> enum
> {
>     version(Linux || OSX)
>     {
>         O_RDONLY = 0,
>         O_WRONLY = 1,
>         O_RDWR = 2,
>         O_CREAT = 0100,
>     }
>     version(Linux)
>     {
>         O_APPEND = 02000,
>     }
>     version(OSX)
>     {
>         O_APPEND = 8,
>         O_SYMLINK = 0x200000,
>     }
> }
> 
> That seems reasonable to me.

Yeah, but I guarantee you that there will be some "common to all" ones 
and an irresistible temptation to put them in outside any version block. 
I also like to have all the enums for one platform in one list, not 
broken up by other stuff for other platforms, because then it is easier 
to verify against the C headers.


> Besides, without expression-level version(), the project's author might just 
> as likely think "Shoot, this is stupid that D doesn't let me make this 
> nicely DRY. But I really like DRY, so I guess I'll just resort to an 
> external C-like pre-processor".

There's something wrong with that option, because although it's always 
been on the table (not just for D, but for any language) nobody ever 
uses it.

Back in the '80s people would often complain about the limitations of 
the C preprocessor, and the answer was always "if you want a real macro 
preprocessor, use m4". But I've never heard of anyone ever actually 
using m4 to preprocess C. The "just use m4" meme became a joke, like Bob 
Villa saying "just use track lighting".