opaque type redesign

README.md

@@ -32,6 +32,8 @@ simpler binding code in many common situations.
 
 Tutorial and reference documentation is provided at
 [http://pybind11.readthedocs.org/en/latest](http://pybind11.readthedocs.org/en/latest).
+A PDF version of the manual is available
+[here](https://media.readthedocs.org/pdf/pybind11/latest/pybind11.pdf).
 
 ## Core features
 pybind11 can map the following core C++ features to Python

docs/advanced.rst

@@ -1203,7 +1203,7 @@ Suppose we bind the following function
        v.push_back(1);
     }
 
-and call it as follows from Python:
+and call it from Python, the following happens:
 
 .. code-block:: python
 
@@ -1244,21 +1244,36 @@ In this case, properties can be read and written in their entirety. However, an
    >>> print(m.contents)
    [5, 6]
 
-To deal with both of the above situations, pybind11 contains a simple template
-wrapper class named ``opaque<T>``.
-
-``opaque<T>`` disables pybind11's template-based conversion machinery for
-``T`` and can be used to treat STL types as opaque objects, whose contents are
-never inspected or extracted (thus, they can be passed by reference).
-The downside of this approach is that it the binding code becomes a bit more
-wordy. The above function can be bound using the following wrapper code:
+To deal with both of the above situations, pybind11 provides a macro named
+``PYBIND11_MAKE_OPAQUE(T)`` that disables the template-based conversion
+machinery of types, thus rendering them *opaque*. The contents of opaque
+objects are never inspected or extracted, hence they can be passed by
+reference. For instance, to turn ``std::vector<int>`` into an opaque type, add
+the declaration
 
 .. code-block:: cpp
 
-   m.def("append_1", [](py::opaque<std::vector<int>> &v) { append_1(v); });
+    PYBIND11_MAKE_OPAQUE(std::vector<int>);
+
+before any binding code (e.g. invocations to ``class_::def()``, etc). This
+macro must be specified at the top level, since instantiates a partial template
+overload. If your binding code consists of multiple compilation units, it must
+be present in every file preceding any usage of ``std::vector<int>``. Opaque
+types must also have a corresponding ``class_`` declaration to associate them
+with a name in Python, and to define a set of available operations:
+
+.. code-block:: cpp
+
+    py::class_<std::vector<int>>(m, "IntVector")
+        .def(py::init<>())
+        .def("clear", &std::vector<int>::clear)
+        .def("pop_back", &std::vector<int>::pop_back)
+        .def("__len__", [](const std::vector<int> &v) { return v.size(); })
+        .def("__iter__", [](std::vector<int> &v) {
+           return py::make_iterator(v.begin(), v.end());
+        }, py::keep_alive<0, 1>()) /* Keep vector alive while iterator is used */
+        // ....
 
-Opaque types must also have a dedicated ``class_`` declaration to define a
-set of admissible operations.
 
 .. seealso::
 

docs/basics.rst

@@ -117,7 +117,7 @@ example can be compiled using the following command
 
 .. code-block:: bash
 
-    $ c++ -O3 -shared -std=c++11 -I <path-to-pybind11>/include `python-config --cflags --ldflags --libs` example.cpp -o example.so
+    $ c++ -O3 -shared -std=c++11 -I <path-to-pybind11>/include `python-config --cflags --ldflags` example.cpp -o example.so
 
 In general, it is advisable to include several additional build parameters
 that can considerably reduce the size of the created binary. Refer to section

example/example14.cpp

@@ -18,22 +18,26 @@ public:
     StringList stringList;
 };
 
+/* IMPORTANT: Disable internal pybind11 translation mechanisms for STL data structures */
+PYBIND11_MAKE_OPAQUE(StringList); 
+
 void init_ex14(py::module &m) {
-    py::class_<py::opaque<StringList>>(m, "StringList")
+    py::class_<StringList>(m, "StringList")
         .def(py::init<>())
-        .def("push_back", [](py::opaque<StringList> &l, const std::string &str) { l->push_back(str); })
-        .def("pop_back", [](py::opaque<StringList> &l) { l->pop_back(); })
-        .def("back", [](py::opaque<StringList> &l) { return l->back(); });
+        .def("pop_back", &StringList::pop_back)
+        /* There are multiple versions of push_back(), etc. Select the right ones. */
+        .def("push_back", (void (StringList::*)(const std::string &)) &StringList::push_back)
+        .def("back", (std::string &(StringList::*)()) &StringList::back)
+        .def("__len__", [](const StringList &v) { return v.size(); })
+        .def("__iter__", [](StringList &v) {
+           return py::make_iterator(v.begin(), v.end());
+        }, py::keep_alive<0, 1>());
 
     py::class_<ClassWithSTLVecProperty>(m, "ClassWithSTLVecProperty")
         .def(py::init<>())
-        /* Need to cast properties to opaque types to avoid pybind11-internal
-           STL conversion code from becoming active */
-        .def_readwrite("stringList", (py::opaque<StringList> ClassWithSTLVecProperty:: *)
-                                     &ClassWithSTLVecProperty::stringList);
+        .def_readwrite("stringList", &ClassWithSTLVecProperty::stringList);
 
-    m.def("print_opaque_list", [](py::opaque<StringList> &_l) {
-        StringList &l = _l;
+    m.def("print_opaque_list", [](const StringList &l) {
         std::cout << "Opaque list: [";
         bool first = true;
         for (auto entry : l) {

example/example14.py

@@ -16,6 +16,8 @@ l.push_back("Element 1")
 l.push_back("Element 2")
 print_opaque_list(l)
 print("Back element is %s" % l.back())
+for i, k in enumerate(l):
+    print("%i/%i : %s" % (i + 1, len(l), k))
 l.pop_back()
 print_opaque_list(l)
 
@@ -36,4 +38,6 @@ print_null_str(return_null_str())
 
 #####
 
-print(return_unique_ptr())
+ptr = return_unique_ptr()
+print(ptr)
+print_opaque_list(ptr)

example/example14.ref

@@ -1,9 +1,12 @@
 Opaque list: [Element 1, Element 2]
 Back element is Element 2
+1/2 : Element 1
+2/2 : Element 2
 Opaque list: [Element 1]
 Opaque list: []
 Opaque list: [Element 1, Element 3]
 Got void ptr : 1234
 None
 Got null str : 0
-[u'some value']
+<example.StringList object at 0x104a47500>
+Opaque list: [some value]

include/pybind11/cast.h

@@ -17,21 +17,6 @@
 #include <limits>
 
 NAMESPACE_BEGIN(pybind11)
-
-/// Thin wrapper type used to treat certain data types as opaque (e.g. STL vectors, etc.)
-template <typename Type> class opaque {
-public:
-    template <typename... Args> opaque(Args&&... args) : value(std::forward<Args>(args)...) { }
-    operator Type&() { return value; }
-    operator const Type&() const { return value; }
-    operator Type*() { return &value; }
-    operator const Type*() const { return &value; }
-    Type* operator->() { return &value; }
-    const Type* operator->() const { return &value; }
-private:
-    Type value;
-};
-
 NAMESPACE_BEGIN(detail)
 
 /// Additional type information which does not fit into the PyTypeObject
@@ -238,11 +223,11 @@ using cast_op_type = typename std::conditional<std::is_pointer<typename std::rem
     typename std::add_lvalue_reference<typename intrinsic_type<T>::type>::type>::type;
 
 /// Generic type caster for objects stored on the heap
-template <typename type, typename Enable = void> class type_caster : public type_caster_generic {
+template <typename type> class type_caster_base : public type_caster_generic {
 public:
     static PYBIND11_DESCR name() { return type_descr(_<type>()); }
 
-    type_caster() : type_caster_generic(typeid(type)) { }
+    type_caster_base() : type_caster_generic(typeid(type)) { }
 
     static handle cast(const type &src, return_value_policy policy, handle parent) {
         if (policy == return_value_policy::automatic || policy == return_value_policy::automatic_reference)
@@ -277,10 +262,12 @@ protected:
     static void *move_constructor(const void *) { return nullptr; }
 };
 
-template <typename type> class type_caster<std::reference_wrapper<type>> : public type_caster<type> {
+template <typename type, typename SFINAE = void> class type_caster : public type_caster_base<type> { };
+
+template <typename type> class type_caster<std::reference_wrapper<type>> : public type_caster_base<type> {
 public:
     static handle cast(const std::reference_wrapper<type> &src, return_value_policy policy, handle parent) {
-        return type_caster<type>::cast(&src.get(), policy, parent);
+        return type_caster_base<type>::cast(&src.get(), policy, parent);
     }
     template <typename T> using cast_op_type = std::reference_wrapper<type>;
     operator std::reference_wrapper<type>() { return std::ref(*((type *) this->value)); }
@@ -461,12 +448,12 @@ protected:
 template <typename type> class type_caster<std::unique_ptr<type>> {
 public:
     static handle cast(std::unique_ptr<type> &&src, return_value_policy policy, handle parent) {
-        handle result = type_caster<type>::cast(src.get(), policy, parent);
+        handle result = type_caster_base<type>::cast(src.get(), policy, parent);
         if (result)
             src.release();
         return result;
     }
-    static PYBIND11_DESCR name() { return type_caster<type>::name(); }
+    static PYBIND11_DESCR name() { return type_caster_base<type>::name(); }
 };
 
 template <> class type_caster<std::wstring> {
@@ -672,14 +659,14 @@ protected:
 };
 
 /// Type caster for holder types like std::shared_ptr, etc.
-template <typename type, typename holder_type> class type_caster_holder : public type_caster<type> {
+template <typename type, typename holder_type> class type_caster_holder : public type_caster_base<type> {
 public:
-    using type_caster<type>::cast;
-    using type_caster<type>::typeinfo;
-    using type_caster<type>::value;
-    using type_caster<type>::temp;
-    using type_caster<type>::copy_constructor;
-    using type_caster<type>::move_constructor;
+    using type_caster_base<type>::cast;
+    using type_caster_base<type>::typeinfo;
+    using type_caster_base<type>::value;
+    using type_caster_base<type>::temp;
+    using type_caster_base<type>::copy_constructor;
+    using type_caster_base<type>::move_constructor;
 
     bool load(handle src, bool convert) {
         if (!src || !typeinfo) {
@@ -790,4 +777,9 @@ template <typename... Args> inline object handle::call(Args&&... args) const {
     return result;
 }
 
+#define PYBIND11_MAKE_OPAQUE(Type) \
+    namespace pybind11 { namespace detail { \
+        template<> class type_caster<Type> : public type_caster_base<Type> { }; \
+    }}
+
 NAMESPACE_END(pybind11)