[cfe-dev] RFC: Function Overloading in C

[Douglas Gregor]

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.

	- Doug