Is it feasible to slowly rewrite a C++ codebase in D?

[bachmeier]

On Wednesday, 20 June 2018 at 18:47:10 UTC, Jordi Gutiérrez 
Hermoso wrote:

> Another possibility might be in dlopen'able functions. 
> Currently Octave uses so-called oct functions, which are 
> nothing more than C++ object code that is dynamically loaded by 
> the interpreter at runtime. They are compiled to the Octave C++ 
> API, but we also have a Matlab-compatible C API that perhaps 
> could be more amenable for D-ification.

Can confirm that dpp works to create mex files. Rewriting the 
mypow2.c example in D:

File mypow3.dpp

#include "mex.h"
import std.conv, std.stdio;

extern(C) void mexFunction(int nlhs, mxArray** plhs,
              int nrhs, const mxArray** prhs) {
   mwSize n;
   mwIndex i;
   double * vri;
   double * vro;

   if (nrhs != 1 || !mxIsDouble(prhs[0]))
     mexErrMsgTxt ("ARG1 must be a double matrix");

   n = mxGetNumberOfElements(prhs[0]).to!int;
   plhs[0] = mxCreateNumericArray (mxGetNumberOfDimensions 
(prhs[0]),
                                   mxGetDimensions (prhs[0]),
                                   mxGetClassID (prhs[0]),
                                   
mxIsComplex(prhs[0]).to!mxComplexity);
   vri = mxGetPr (prhs[0]);
   vro = mxGetPr (plhs[0]);

   if (mxIsComplex (prhs[0])) {
       double* vii, vio;
       vii = mxGetPi (prhs[0]);
       vio = mxGetPi (plhs[0]);

       for (i = 0; i < n; i++)
         {
           vro[i] = vri[i] * vri[i] - vii[i] * vii[i];
           vio[i] = 2 * vri[i] * vii[i];
         }
   } else {
       for (i = 0; i < n; i++)
         vro[i] = vri[i] * vri[i];
     }
}

Create the shared library using the information provided by 
mkoctfile:

d++ -c -fPIC --include-path /usr/include/octave-4.2.2/octave/.. \
--include-path /usr/include/octave-4.2.2/octave \
--include-path /usr/include/hdf5/serial mypow3.dpp

dmd -shared -defaultlib=libphobos2.so -of=mypow3.mex mypow3.o \
-L/usr/lib/x86_64-linux-gnu/liboctinterp.so \
-L/usr/lib/x86_64-linux-gnu/liboctave.so


In Octave:

>> b = randn (4,1);
>> mypow3(b)
ans =

    0.45984
    3.54732
    0.30075
    2.09107