[cfe-dev] RFC: Function Overloading in C

[Douglas Gregor]

On Feb 13, 2009, at 9:01 AM, Fariborz Jahanian wrote:

>
> On Feb 13, 2009, at 8:39 AM, Douglas Gregor wrote:
>
>>
>> On Feb 13, 2009, at 2:01 AM, Sebastian Redl wrote:
>>
>>> Douglas Gregor wrote:
>>>> Hi all,
>>>>
>>>> I've just finished the implementation of the "overloadable"  
>>>> function
>>>> attribute that introduces function overloading into C. The intent  
>>>> is
>>>> to make it easier to implement "type-generic" functions (such as
>>>> those
>>>> in tgmath.h and altivec.h). The feature is in Clang's trunk, and is
>>>> documented here:
>>>>
>>>> 	http://clang.llvm.org/docs/LanguageExtensions.html#overloading- 
>>>> in-c
>>>>
>>>> Comments welcome!
>>>>
>>> I wonder if it's possible (and a good idea) to use the C++ linkage
>>> specification syntax for this, i.e.
>>>
>>> extern "C++" double tgsin(double d) { return sin(d); }
>>> extern "C++" float tgsin(float f) { return sinf(f); }
>>> extern "C++" long double tgsin(long double d) { return sinl(d); }
>>>
>>> As a C++ programmer, it looks more natural to me.
>>
>> Huh. I never even thought of that!
>>
>>> Of course, I have no
>>> idea how this would look to a pure C programmer. Also, this syntax
>>> would
>>> imply that we will always mangle this like C++ names.
>>
>>
>> I'm on the fence with this one. My main concern is that 'extern "C+ 
>> +"'
>> is very open-ended, and users seeing this in code might be tempted to
>> try all sorts of crazy C++ things following the 'extern "C++"'. We'll
>> need to make sure we reject all those, otherwise they might work and
>> users might start relying on them :)
>>
>> I like the "overloadable" attribute better in this regard, because it
>> is (was) easy to lock it down and make it only work in very specific
>> circumstances. Plus, it gives us a lot of wiggle room w.r.t. the
>> mangling of these names.
>
> It looks weird to apply extern "C++' on an overloadable 'static'  
> function.

Good point! These functions will usually be inline static, e.g.,

   extern "C++" inline static tgsin(double d) { return sin(d); }

is rather confusing.

Now I definitely like __attribute__((overloadable)) best.

   - Doug