On Thu, Jun 22, 2017 at 10:16:51AM +0200, Jacob Carlborg via Digitalmars-d wrote:
> On 2017-06-22 00:19, H. S. Teoh via Digitalmars-d wrote:
> 
> > The code template says:
> > 
> > 	extern(C) double funcImpl(double x, double y)
> > 
> > But the function pointer type is declared as:
> > 
> > 	alias FuncImpl = double function(double, double);
> > 
> > Notice the lack of `extern(C)` in the latter.
[...]
> You could also add a template that generates a function pointer based on the actual function, "funcImpl" in this case. Something like:
> 
> extern(C) double funcImpl(double x, double y);
> 
> alias FuncImpl = generateFunctionPointer!(funcImpl);
> 
> generateFunctionPointer would evaluate to a function pointer type with the correct signature and calling conventions by inspecting the passed in function symbol. This would avoid that the signatures get out of sync and is a bit more DRY as well.
[...]

Unfortunately, funcImpl's declaration doesn't exist in the main program; it's part of a string used for generating the source code for the shared library.  I *could* factor it out from the string, I suppose, and use a mixin to extract the type of its function pointer.

Hmm, come to think of it, maybe that's what I'll do!  The fact that you can do this at all (i.e., use the same string to generate both the output file and an in-language declaration) is a testament to just how cool D is.  In C/C++ you could use macros to achieve the same thing via stringization, I suppose, but it's uglier.


T

-- 
2+2=4. 2*2=4. 2^2=4. Therefore, +, *, and ^ are the same operation.