translate a macro to D

[teo]

On Fri, 08 Jul 2011 09:54:40 -0400, Steven Schveighoffer wrote:

> On Thu, 07 Jul 2011 16:23:33 -0400, teo <teo.ubuntu at yahoo.com> wrote:
> 
>> On Thu, 07 Jul 2011 11:57:51 -0400, Steven Schveighoffer wrote:
>>
>>> Well, I can't really say I understand the point of using this macro at
>>> all.  sizeof is a builtin, and part of the C spec.  Why not just use
>>> sizeof?
>>>
>>>
>> Well, have a look please at ioctl.h (linux). You will find the
>> following macros:
>>
>>
>> #define _IOC(dir,type,nr,size) \
>>         (((dir)  << _IOC_DIRSHIFT) | \
>>          ((type) << _IOC_TYPESHIFT) | \
>>          ((nr)   << _IOC_NRSHIFT) | \
>>          ((size) << _IOC_SIZESHIFT))
>>
>> #define _IOC_TYPECHECK(t) (sizeof(t))
>>
>> /* used to create numbers */
>> #define _IO(type,nr)            _IOC(_IOC_NONE,(type),(nr),0) #define
>> _IOR(type,nr,size)
>> _IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK (size)))
>> #define _IOW(type,nr,size)      _IOC(_IOC_WRITE,(type),(nr),
>> (_IOC_TYPECHECK(size)))
>> #define _IOWR(type,nr,size)     _IOC(_IOC_READ|_IOC_WRITE,(type),(nr),
>> (_IOC_TYPECHECK(size)))
>>
>>
>> This is what I am after. However I thought that a simplified case will
>> make it easier to describe the problem.
>>
>>
> Hm... I once wrote a D module that accessed a linux device driver (ipmi
> driver to be specific).  I did it in D1, and I used CTFE.  For sure,
> t.sizeof should work instead of _IOC_TYPECHECK.  But Linux supports a
> multitude of CPUs, perhaps other CPUs need a different macro for this.
> It's the only thing I can think of to explain having a specific macro to
> do sizeof.
> 
> -Steve


Steve,

I translated those macros to regular functions and it works that way 
(using T.sizeof), however I could have used a function template instead 
as you suggested before and therefore I have a question:

Are there any benefits of using function templates instead of regular 
functions in that particular case?
The above leads me to another question: are those functions evaluated at 
compile-time? I suppose they are not.

Here an example usage:

uint _IOC(uint dir, uint type, uint nr, uint size)
{
  return (dir << _IOC_DIRSHIFT) | (type << _IOC_TYPESHIFT) | (nr << 
_IOC_NRSHIFT) | (size << _IOC_SIZESHIFT);
}
uint _IO(uint type, uint nr)
{
  return _IOC(_IOC_NONE, type, nr, 0);
}
uint _IOWR(uint type, uint nr, uint size)
{
  return _IOC(_IOC_READ | _IOC_WRITE, type, nr, size);
}

In another module define the constants:
const C1 = _IO(1, 2);
const C2 = _IOWR(2, 3, A.sizeof);