PageRenderTime 4ms CodeModel.GetById 1ms app.highlight 1ms RepoModel.GetById 1ms app.codeStats 0ms

/trunk/Examples/perl5/reference/index.html

#
HTML | 146 lines | 115 code | 31 blank | 0 comment | 0 complexity | 1e0710c3ad5c8adcd9fab88b7c1089eb MD5 | raw file
  1<html>
  2<head>
  3<title>SWIG:Examples:perl5:reference</title>
  4</head>
  5
  6<body bgcolor="#ffffff">
  7
  8
  9<tt>SWIG/Examples/perl5/reference/</tt>
 10<hr>
 11
 12<H2>C++ Reference Handling</H2>
 13
 14<p>
 15This example tests SWIG's handling of C++ references.  Since C++
 16references are closely related to pointers (as both refer to a
 17location in memory), SWIG simply collapses all references into
 18pointers when creating wrappers.
 19
 20<h2>Some examples</h2>
 21
 22References are most commonly used as function parameter.  For example,
 23you might have an operator like this:
 24
 25<blockquote>
 26<pre>
 27Vector operator+(const Vector &amp;a, const Vector &amp;b) {
 28   Vector result;
 29   result.x = a.x + b.x;
 30   result.y = a.y + b.y;
 31   result.z = a.z + b.z;
 32   return result;
 33}
 34</pre>
 35</blockquote>
 36
 37or a function:
 38
 39<blockquote>
 40<pre>
 41Vector addv(const Vector &amp;a, const Vector &amp;b) {
 42   Vector result;
 43   result.x = a.x + b.x;
 44   result.y = a.y + b.y;
 45   result.z = a.z + b.z;
 46   return result;
 47}
 48</pre>
 49</blockquote>
 50
 51In these cases, SWIG transforms everything into a pointer and creates a wrapper
 52that looks like this:
 53
 54<blockquote>
 55<pre>
 56Vector wrap_addv(Vector *a, Vector *b) {
 57    return addv(*a,*b);
 58}
 59</pre>
 60</blockquote>
 61
 62Occasionally, a reference is used as a return value of a function
 63when the return result is to be used as an lvalue in an expression.
 64The prototypical example is an operator like this:
 65
 66<blockquote>
 67<pre>
 68Vector &amp;operator[](int index);
 69</pre>
 70</blockquote>
 71
 72or a method:
 73
 74<blockquote>
 75<pre>
 76Vector &amp;get(int index);
 77</pre>
 78</blockquote>
 79
 80For functions returning references, a wrapper like this is created:
 81
 82<blockquote>
 83<pre>
 84Vector *wrap_Object_get(Object *self, int index) {
 85    Vector &amp;result = self-&gt;get(index);
 86    return &amp;result;
 87}
 88</pre>
 89</blockquote>
 90
 91The following <a href="example.h">header file</a> contains some class
 92definitions with some operators and use of references.
 93
 94<h2>SWIG Interface</h2>
 95
 96SWIG does NOT support overloaded operators so it can not directly build
 97an interface to the classes in the above file.   However, a number of workarounds
 98can be made.  For example, an overloaded operator can be stuck behind a function
 99call such as the <tt>addv()</tt> function above.  Array access can be handled
100with a pair of set/get functions like this:
101
102<blockquote>
103<pre>
104class VectorArray {
105public:
106 ...
107   %addmethods {
108    Vector &amp;get(int index) {
109      return (*self)[index];
110    }
111    void set(int index, Vector &amp;a) {
112      (*self)[index] = a;
113    }
114   }
115   ...
116}
117</pre>
118</blockquote>
119
120Click <a href="example.i">here</a> to see a SWIG interface file with these additions.
121
122<h2>Sample Perl script</h2>
123
124Click <a href="runme.pl">here</a> to see a script that manipulates some C++ references.
125
126<h2>Notes:</h2>
127
128<ul>
129<li>C++ references primarily provide notational convenience for C++
130source code.  However, it doesn't much matter to Perl.
131
132<p>
133<li>When a program returns a reference, a pointer is returned.
134Unlike return by value, memory is not allocated to hold the
135return result.
136
137<p>
138<li>SWIG has particular trouble handling various combinations of references
139and pointers.  This is side effect of an old parsing scheme and
140type representation that will be replaced in future versions.
141
142</ul>
143
144<hr>
145</body>
146</html>