_argptr woes

[Bill Baxter]

Frits van Bommel wrote:
> kris wrote:
>> The D spec says:
>>
>> "The implementiations of these variadic functions have a special local 
>> variable declared for them, _argptr, which is a void* pointer to the 
>> first of the variadic arguments. To access the arguments, _argptr must 
>> be cast to a pointer to the expected argument type"
>>
>>
>> To me, this means that a D compiler must implement _argptr in these 
>> terms. Is that indeed the case, Walter? Or is my interpretation 
>> incorrect?
> 
> That would seem to be what it means.
> That would also seem to be a pretty big portability bug in the spec. On 
> amd64 definitely !is(va_list == void*) :P. (at least for current GDC, 
> GCC and any other compiler following 
> http://www.x86-64.org/documentation/abi.pdf)

Sounds like a good opportunity to replace the whole _argptr/_arguments 
hack with something more D-like.  Something more like a TypeInfo.  Say, 
  a VarArgInfo class which provides slightly higher level access to the 
void*/TypeInfo[] pair.  Then make it possible to use that as the last 
argument to the vararg function:

     int foo(char[] fmt, ... v) {
         // v is a VarArgInfo here
     }

Nice thing is this can coexist with _argptr/_arguments code.  If you 
don't specify a variable name for the vararg, you get _argptr/_arguments 
behavior.  If you do specify then you get a VarArgInfo with the 
specified name.

--bb