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Move joel's updates over from the main trunk (finish)
[SVN r15870]
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Dave Abrahams
@@ -142,7 +142,7 @@ or more policies can be composed by chaining. Here's the general syntax:</p>
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</span></pre></code>
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<p>
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Here is the list of predefined call policies. A complete reference detailing
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these can be found <a href="../../v2/CallPolicies.html">
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these can be found <a href="../../v2/reference.html#models_of_call_policies">
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here</a>.</p>
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<ul><li><b>with_custodian_and_ward</b><br> Ties lifetimes of the arguments</li><li><b>with_custodian_and_ward_postcall</b><br> Ties lifetimes of the arguments and results</li><li><b>return_internal_reference</b><br> Ties lifetime of one argument to that of result</li><li><b>return_value_policy<T> with T one of:</b><br></li><li><b>reference_existing_object</b><br>naïve (dangerous) approach</li><li><b>copy_const_reference</b><br>Boost.Python v1 approach</li><li><b>copy_non_const_reference</b><br></li><li><b>manage_new_object</b><br> Adopt a pointer and hold the instance</li></ul><table width="80%" border="0" align="center">
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<tr>
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@@ -56,12 +56,11 @@ Then, in Python:</p>
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Note that <tt>name</tt> is exposed as <b>read-only</b> while <tt>value</tt> is exposed
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as <b>read-write</b>.</p>
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<code><pre>
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<span class=special>>>> </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>name </span><span class=special>= </span><span class=literal>'e' </span>#<span class=identifier>can</span><span class=literal>'t change name
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>>> x.name = 'e' # can't change name
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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AttributeError: can'</span><span class=identifier>t </span><span class=identifier>set </span><span class=identifier>attribute
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</span></pre></code>
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<table border="0">
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AttributeError: can't set attribute
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</pre></code><table border="0">
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<tr>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><a href="constructors.html"><img src="theme/l_arr.gif" border="0"></a></td>
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@@ -92,15 +92,16 @@ polymorphically <i>from</i> <b>C++</b>. </td>
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<p>
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Wrapping <tt>Base</tt> and the free function <tt>call_f</tt>:</p>
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<code><pre>
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<span class=identifier>class_</span><span class=special><</span><span class=identifier>Base</span><span class=special>, </span><span class=identifier>BaseWrap</span><span class=special>, </span><span class=identifier>noncopyable</span><span class=special>>(</span><span class=string>"Base"</span><span class=special>, </span><span class=identifier>no_init</span><span class=special>)
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<span class=identifier>class_</span><span class=special><</span><span class=identifier>Base</span><span class=special>, </span><span class=identifier>BaseWrap</span><span class=special>, </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>noncopyable</span><span class=special>>(</span><span class=string>"Base"</span><span class=special>, </span><span class=identifier>no_init</span><span class=special>)
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</span><span class=special>;
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</span><span class=identifier>def</span><span class=special>(</span><span class=string>"call_f"</span><span class=special>, </span><span class=identifier>call_f</span><span class=special>);
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</span></pre></code>
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<p>
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Notice that we parameterized the <tt>class_</tt> template with <tt>BaseWrap</tt> as the
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second parameter. What is <tt>noncopyable</tt>? Without it, the library will try
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to instantiate a copy constructor for returning Base objects from
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functions.</p>
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to create code for converting Base return values of wrapped functions to
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Python. To do that, it needs Base's copy constructor... which isn't
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available, since Base is an abstract class.</p>
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<p>
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In Python, let us try to instantiate our <tt>Base</tt> class:</p>
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<code><pre>
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@@ -64,7 +64,7 @@ expose instead.</p>
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<p>
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<tt>init<std::string>()</tt> exposes the constructor taking in a
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<tt>std::string</tt> (in Python, constructors are spelled
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"<tt>__init__(...)</tt>").</p>
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"<tt>"__init__"</tt>").</p>
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<p>
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We can expose additional constructors by passing more <tt>init<...></tt>s to
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the <tt>def()</tt> member function. Say for example we have another World
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@@ -70,18 +70,21 @@ member functions.</p>
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<p>
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Demonstrates that you can write the C++ equivalent of <tt>"format" % x,y,z</tt>
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in Python, which is useful since there's no easy way to do that in std C++.</p>
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<table width="80%" border="0" align="center">
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<tr>
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<td class="note_box">
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<img src="theme/alert.gif"></img> Beware the common pitfall of
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forgetting that the constructors of most of Python's mutable types
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make copies, just as in Python.<br><br>
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<tt>dict d(x.attr("__dict__")); # makes a copy of x's dict<br>
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d['whatever'] = 3; # modifies a copy of x.__dict__ (not the original)<br></tt>
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</td>
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</tr>
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</table>
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<p>
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<img src="theme/alert.gif"></img> <b>Beware</b> the common pitfall of forgetting that the constructors
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of most of Python's mutable types make copies, just as in Python.</p>
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<p>
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Python:</p>
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<code><pre>
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<span class=special>>>> </span><span class=identifier>d </span><span class=special>= </span><span class=identifier>dict</span><span class=special>(</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__</span><span class=special>) </span>#<span class=identifier>copies </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__
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</span><span class=special>>>> </span><span class=identifier>d</span><span class=special>[</span><span class=literal>'whatever'</span><span class=special>] </span>#<span class=identifier>modifies </span><span class=identifier>the </span><span class=identifier>copy
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</span></pre></code>
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<p>
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C++:</p>
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<code><pre>
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<span class=identifier>dict </span><span class=identifier>d</span><span class=special>(</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>"__dict__"</span><span class=special>)); </span>#<span class=identifier>copies </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__
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</span><span class=identifier>d</span><span class=special>[</span><span class=literal>'whatever'</span><span class=special>] </span><span class=special>= </span><span class=number>3</span><span class=special>; </span>#<span class=identifier>modifies </span><span class=identifier>the </span><span class=identifier>copy
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</span></pre></code>
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<a name="class__lt_t_gt__as_objects"></a><h2>class_<T> as objects</h2><p>
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Due to the dynamic nature of Boost.Python objects, any <tt>class_<T></tt> may
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also be one of these types! The following code snippet wraps the class
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