Defining a version after it's tested for

[Tim Matthews]

On Fri, 22 May 2009 07:54:07 +1200, Robert Clipsham
<robert at octarineparrot.com> wrote:

> Steven Schveighoffer wrote:
>> Versions are intended to be predefined before usage.  It's the same  
>> thing as using a variable before it's defined.  The rational is, to  
>> flag errors to the user where he thinks forward referencing of versions  
>> works.
>>  Unfortunately, you have to do the following workaround:
>>  version(BackendFoo) { version=BackendFoo_;}
>> else version(BackendBar) { version=BackendBar_;}
>> else version(BackendCar) { version=BackendCar_;}
>> else
>> {
>>   version(Windows) {version=BackendFoo_;}
>> }
>>  And now, you must use Backend*_ in your code.  It should work, but  
>> it's ugly.
>>  Maybe Walter has a better method.
>>  -Steve
>
> Unfortunately I thought this might be the case. Thanks.

I think this would be less ugly:

template vers(char[] V)
{
      mixin("version(" ~ V ~ ")
      {
            const bool vers = true;
      }
      else
      {
            const bool vers = false;
      }");
}

static if(vers!("BackendFoo") || vers!("Windows"))
{
       //
}
else static if(vers!("BackendBar"))
{
      //
}
else static if (vers!("BackendCar"))
{
     //
}
else
{
     //
}

I would prefer the normal version statement to work like that directly  
though.