SWIG/Examples/go/template/

C++ template support

This example illustrates how C++ templates can be used from Go using SWIG.

The C++ Code

Let's take a templated function and a templated class as follows: 
/* File : example.h */

// Some template definitions

template T max(T a, T b) { return  a>b ? a : b; }

template class vector {
  T *v;
  int sz;
 public:
  vector(int _sz) {
    v = new T[_sz];
    sz = _sz;
  }
  T &get(int index) {
    return v[index];
  }
  void set(int index, T &val) {
    v[index] = val;
  }
#ifdef SWIG
  %addmethods {
    T getitem(int index) {
      return self->get(index);
    }
    void setitem(int index, T val) {
      self->set(index,val);
    }
  }
#endif
};
The %addmethods is used for a neater interface from Go as the functions get and set use C++ references to primitive types. These are tricky to use from Go as they end up as pointers, which only work when the C++ and Go types correspond precisely.

The SWIG interface

A simple SWIG interface for this can be built by simply grabbing the header file like this: 
/* File : example.i */
%module example

%{
#include "example.h"
%}

/* Let's just grab the original header file here */
%include "example.h"

/* Now instantiate some specific template declarations */

%template(maxint) max;
%template(maxdouble) max;
%template(vecint) vector;
%template(vecdouble) vector;
Note that SWIG parses the templated function max and templated class vector and so knows about them. However to generate code for use from Go, SWIG has to be told which class/type to use as the template parameter. The SWIG directive %template is used for this.

A sample Go program

Click here to see a Go program that calls the C++ functions from Go.

Notes

Use templated classes just like you would any other SWIG generated Go class. Use the classnames specified by the %template directive. 
vecdouble dv = new vecdouble(1000);
dv.setitem(i, 12.34));