From 152a3f2e5fa997d4168163db3386d8143067f8e6 Mon Sep 17 00:00:00 2001 From: Dave Abrahams Date: Wed, 8 May 2002 03:23:58 +0000 Subject: [PATCH] initial commit [SVN r13737] --- doc/v2/ptr.html | 261 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 261 insertions(+) create mode 100644 doc/v2/ptr.html diff --git a/doc/v2/ptr.html b/doc/v2/ptr.html new file mode 100644 index 00000000..d404ba1a --- /dev/null +++ b/doc/v2/ptr.html @@ -0,0 +1,261 @@ + + + + + + Boost.Python - <boost/python/ptr.hpp> + + + +
+

+

+ + 		+

Boost.Python

+ +

Header <boost/python/ptr.hpp>

+
+
+ +

Contents

+ +
+
Introduction + +
Functions +
+
+
ptr +
+ +
Classes +
+
+
Class template pointer_wrapper + +
+
+
Class template pointer_wrapper synopsis + +
Class + pointer_wrapper types + +
Class + pointer_wrapper constructors and destructor + +
Class + pointer_wrapper observer functions + +
+
+ +
Metafunctions +
+
+
Class template is_pointer_wrapper + +
+
+
Class template is_pointer_wrapper synopsis +
+ + +
Class template unwrap_pointer + +
+
+
Class template unwrap_pointer synopsis +
+ +
+ + +
Example(s) +
+
+ +

Introduction

+ +

<boost/python/ptr.hpp> defines the + ptr() function template, which allows users to + specify how to convert C++ pointer values to python in the context + of implementing overridable virtual functions, invoking Python + callable objects, or explicitly converting C++ objects to + Python. Normally, when passing pointers to Python callbacks, the + pointee is copied to ensure that the Python object + never holds a dangling reference. To specify that the new Python + object should merely contain a copy of a pointer p, + the user can pass ptr(p) instead of passing + p directly. This interface is meant to mirror the use + of boost::ref(), + which can be similarly used to prevent copying of referents. + +

ptr(p) returns an instance of pointer_wrapper<>, which + can be detected using the is_pointer_wrapper<> + metafunction; unwrap_pointer<> is a + metafunction which extracts the original pointer type from a + pointer_wrapper<>. These classes can be thought + of as implementation details. + +

Functions

+
+
+template <class T>
+pointer_wrapper<T> ptr(T x);
+
+ +
+
Requires: T is a pointer type. + +
Returns: pointer_wrapper<T>(x) + +
Throws: nothing. +
+ +

Classes

+ +

Class template pointer_wrapper

+ +

A "type envelope" which is returned by ptr(), used to indicate reference semantics + for pointers passed to Python callbacks. + +

Class + pointer_wrapper synopsis

+
+namespace boost
+{
+    template<class Ptr> class pointer_wrapper
+    { 
+     public:
+        typedef Ptr type;
+
+        explicit pointer_wrapper(Ptr x);
+        operator Ptr() const;
+        Ptr get() const;
+    };
+};
+
+ +

Class template pointer_wrapper types

+
+typedef Ptr type;
+
+The type of the pointer being wrapped. + +

Class template pointer_wrapper constructors and + destructor

+
+explicit pointer_wrapper(Ptr x);
+
+ +
+
Requires: Ptr is a pointer type. + +
Effects: Stores x in a the pointer_wrapper<>. +
Throws: nothing. +
+ +

Class template pointer_wrapper observer + functions

+
+operator Ptr() const;
+Ptr get() const;
+
+ +
+
Returns: a copy of the stored pointer. +
Rationale: pointer_wrapper is intended + to be a stand-in for the actual pointer type, but sometimes it's + better to have an explicit way to retrieve the pointer. +
+ +

Class template is_pointer_wrapper

+ +

A unary metafunction whose value is true iff its + argument is a pointer_wrapper<>. + +

Class template is_pointer_wrapper synopsis

+
+namespace boost
+{
+    template<class T> class is_pointer_wrapper
+    { 
+        static unspecified value = ...;
+    };
+};
+
+ + +
+
Returns: true iff T is a + specialization of +pointer_wrapper<>. +
value is an integral constant convertible to bool of +unspecified type + +
+ +

Class template unwrap_pointer

+ +A unary metafunction which extracts the wrapped pointer type from a +specialization of pointer_wrapper<>. + +

Class template unwrap_pointer synopsis

+
+namespace boost
+{
+    template<class T> class unwrap_pointer
+    { 
+        typedef unspecified type;
+    };
+};
+
+ +
+
Returns: T::type if T is a + specialization of +pointer_wrapper<>, T otherwise +
+ + +

Example(s)

+ +This example illustrates the use of ptr() to prevent an +object from being copied: +
+#include <boost/python/call.hpp>
+#include <boost/python/ptr.hpp>
+
+class expensive_to_copy
+{
+   ...
+};
+
+void pass_as_arg(expensive_to_copy* x, PyObject* f)
+{
+   // call the Python function f, passing a Python object built around
+   // which refers to *x by-pointer.
+   //
+   // *** Note: ensuring that *x outlives the argument to f() is    ***
+   // *** up to the user! Failure to do so could result in a crash! ***
+
+   boost::python::call<void>(f, ptr(x));
+}
+...
+
+ +

Revised + + 07 May, 2002 + + + +

© Copyright Dave + Abrahams 2002. All Rights Reserved. +