Why version() ?

[Sergey Gromov]

Tue, 10 Feb 2009 19:57:47 -0800, Walter Bright wrote:

> 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.

There's Antenna for Java.  It's nearly impossible to do without some
preprocessor in Java if you want some mid-level library to work reliably
on many different mobile phones.  Compile once, run anywhere--sounds
like a joke to me.