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<title>SWIG:Examples:go:template</title>
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<tt>SWIG/Examples/go/template/</tt>
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<H2>C++ template support</H2>

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

<h2>The C++ Code</h2>

Lets take a templated function and a templated class as follows:

<blockquote>
<pre>
/* File : example.h */

// Some template definitions

template<class T> T max(T a, T b) { return  a&gt;b ? a : b; }

template<class T> class vector {
  T *v;
  int sz;
 public:
  vector(int _sz) {
    v = new T[_sz];
    sz = _sz;
  }
  T &amp;get(int index) {
    return v[index];
  }
  void set(int index, T &amp;val) {
    v[index] = val;
  }
#ifdef SWIG
  %addmethods {
    T getitem(int index) {
      return self-&gt;get(index);
    }
    void setitem(int index, T val) {
      self-&gt;set(index,val);
    }
  }
#endif
};
</pre>
</blockquote>
The %addmethods is used for a neater interface from Go as the
functions <tt>get</tt> and <tt>set</tt> 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.

<h2>The SWIG interface</h2>

A simple SWIG interface for this can be built by simply grabbing the
header file like this:

<blockquote>
<pre>
/* 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<int>;
%template(maxdouble) max<double>;
%template(vecint) vector<int>;
%template(vecdouble) vector<double>;
</pre>
</blockquote>

Note that SWIG parses the templated function <tt>max</tt> and
templated class <tt>vector</tt> 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.

<h2>A sample Go program</h2>

Click <a href="runme.go">here</a> to see a Go program that calls the
C++ functions from Go.

<h2>Notes</h2> Use templated classes just like you would any other
SWIG generated Go class. Use the classnames specified by the %template
directive.

<blockquote>
<pre>
vecdouble dv = new vecdouble(1000);
dv.setitem(i, 12.34));
</pre>
</blockquote>

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