version()

[Manu]

On 16 January 2012 15:30, Don Clugston <dac at nospam.com> wrote:

> On 16/01/12 01:08, Jonathan M Davis wrote:
>
>> On Monday, January 16, 2012 01:44:56 Manu wrote:
>>
>>> Surely basic logical expressions within a version seem not only logical,
>>> but also very necessary?
>>> There must be a reason this is impossible, or else I can't believe it's
>>> not
>>> already like that...
>>>
>>
>> People have requested it. Walter is against it. I don't remember his exact
>> arguments, but he believes that it leads to worse code if you allow it.
>>
>> As for
>>
>> version(linux || OSX)
>>
>> you can use
>>
>> version(Posix)
>>
>> It'll include FreeBSD as well, but then again, if something is common to
>> both
>> linux and OSX, then it's almost certainly in FreeBSD as well.
>>
>> - Jonathan M Davis
>>
>
> I think both approaches are wrong. I think the idea approach is to treat
> versions as booleans, and have a one-definition rule.
>
> version VersionIdentifier = VersionExpression;
>
> extern version VersionIdentifier;
> // means this version is set from command line, or is a compiler built-in
>
> VersionExpression:
>        VersionExpression && VersionExpression
>        VersionExpression || VersionExpression
>        !VersionExpression
>        ( VersionExpression )
>        VersionIdentifier
>        true
>        false
>
> version(A)
> {
>   version = AorNotB;
> }
> version(B)
> {
> }
> else {
>   version = AorNotB;
> }
>
> becomes:
> version AorNotB = A || !B;
>
> Make it illegal to reference a version identifier which hasn't been
> declared. Disallow version declarations inside version blocks, and all the
> spaghetti is gone.
>

Will that work? I don't think it's reasonable to expect all versions to be
declared in all cases/platforms. There are SSE version identifiers for
instance, why would they be defined on a PPC platform? Likewise any
platform specific features...
Otherwise I generally agree. Though again, too much water under the bridge
to change this decision in the language.

The only realistic thing I can see that could be done without breaking
anything is to allow basic logical expressions of version keys which would
otherwise still follow the existing idiom.
Alternatively, allow static-if to access the version list/map. If the
version list was known to static-if, it could take care of the same job,
though it would probably be considerably more ugly.
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