Commit 37534635 authored by Robert Bradshaw's avatar Robert Bradshaw

Update C++ Rectangle example.

parent cb0e2dc3
...@@ -48,11 +48,11 @@ document. Let's assume it will be in a header file called ...@@ -48,11 +48,11 @@ document. Let's assume it will be in a header file called
class Rectangle { class Rectangle {
public: public:
int x0, y0, x1, y1; int x0, y0, x1, y1;
Rectangle();
Rectangle(int x0, int y0, int x1, int y1); Rectangle(int x0, int y0, int x1, int y1);
~Rectangle(); ~Rectangle();
int getLength();
int getHeight();
int getArea(); int getArea();
void getSize(int* width, int* height)
void move(int dx, int dy); void move(int dx, int dy);
}; };
} }
...@@ -65,6 +65,8 @@ and the implementation in the file called :file:`Rectangle.cpp`: ...@@ -65,6 +65,8 @@ and the implementation in the file called :file:`Rectangle.cpp`:
namespace shapes { namespace shapes {
Rectangle::Rectangle() { }
Rectangle::Rectangle(int X0, int Y0, int X1, int Y1) { Rectangle::Rectangle(int X0, int Y0, int X1, int Y1) {
x0 = X0; x0 = X0;
y0 = Y0; y0 = Y0;
...@@ -74,18 +76,15 @@ and the implementation in the file called :file:`Rectangle.cpp`: ...@@ -74,18 +76,15 @@ and the implementation in the file called :file:`Rectangle.cpp`:
Rectangle::~Rectangle() { } Rectangle::~Rectangle() { }
int Rectangle::getLength() {
return (x1 - x0);
}
int Rectangle::getHeight() {
return (y1 - y0);
}
int Rectangle::getArea() { int Rectangle::getArea() {
return (x1 - x0) * (y1 - y0); return (x1 - x0) * (y1 - y0);
} }
void Rectangle::getSize(int *width, int *height) {
width = x1 - x0;
height = y1 - y0;
}
void Rectangle::move(int dx, int dy) { void Rectangle::move(int dx, int dy) {
x0 += dx; x0 += dx;
y0 += dy; y0 += dy;
...@@ -192,11 +191,11 @@ We now need to declare the attributes and methods for use on Cython:: ...@@ -192,11 +191,11 @@ We now need to declare the attributes and methods for use on Cython::
cdef extern from "Rectangle.h" namespace "shapes": cdef extern from "Rectangle.h" namespace "shapes":
cdef cppclass Rectangle: cdef cppclass Rectangle:
Rectangle() except +
Rectangle(int, int, int, int) except + Rectangle(int, int, int, int) except +
int x0, y0, x1, y1 int x0, y0, x1, y1
int getLength()
int getHeight()
int getArea() int getArea()
void getSize(int* width, int* height)
void move(int, int) void move(int, int)
Note that the constructor is declared as "except +". If the C++ code or Note that the constructor is declared as "except +". If the C++ code or
...@@ -229,7 +228,7 @@ a "default" constructor:: ...@@ -229,7 +228,7 @@ a "default" constructor::
... ...
Note that, like C++, if the class has only one constructor and it Note that, like C++, if the class has only one constructor and it
is a default one, it's not necessary to declare it. is a nullary one, it's not necessary to declare it.
Create Cython wrapper class Create Cython wrapper class
---------------------------- ----------------------------
...@@ -239,33 +238,53 @@ of the C++ Rectangle type. Now, we need to make this accessible from ...@@ -239,33 +238,53 @@ of the C++ Rectangle type. Now, we need to make this accessible from
external Python code (which is our whole point). external Python code (which is our whole point).
Common programming practice is to create a Cython extension type which Common programming practice is to create a Cython extension type which
holds a C++ instance pointer as an attribute ``thisptr``, and create a bunch of holds a C++ instance as an attribute and create a bunch of
forwarding methods. So we can implement the Python extension type as:: forwarding methods. So we can implement the Python extension type as::
cdef class PyRectangle: cdef class PyRectangle:
cdef Rectangle *thisptr # hold a C++ instance which we're wrapping cdef Rectangle c_rect # hold a C++ instance which we're wrapping
def __cinit__(self, int x0, int y0, int x1, int y1): def __cinit__(self, int x0, int y0, int x1, int y1):
self.thisptr = new Rectangle(x0, y0, x1, y1) self.c_rect = Rectangle(x0, y0, x1, y1)
def __dealloc__(self): def get_area(self):
del self.thisptr return self.c_rect.getArea()
def getLength(self): def get_size(self)
return self.thisptr.getLength() int width, int height
def getHeight(self): self.c_rect.getSize(&width, &height)
return self.thisptr.getHeight() return width, height
def getArea(self):
return self.thisptr.getArea()
def move(self, dx, dy): def move(self, dx, dy):
self.thisptr.move(dx, dy) self.c_rect.move(dx, dy)
And there we have it. From a Python perspective, this extension type will look And there we have it. From a Python perspective, this extension type will look
and feel just like a natively defined Rectangle class. If you want to give and feel just like a natively defined Rectangle class.
It should be noted that
If you want to give
attribute access, you could just implement some properties:: attribute access, you could just implement some properties::
property x0: @property
def __get__(self): return self.thisptr.x0 def x0(self):
def __set__(self, x0): self.thisptr.x0 = x0 return self.c_rect.x0
@x0.setter
def x0(self):
def __set__(self, x0): self.c_rect.x0 = x0
... ...
Cython initializes C++ class attributes of a cdef class using the nullary constructor.
If the class you're wrapping does not have a nullary constructor, you must store a pointer
to the wrapped class and manually allocate and deallocate it.
A convienient and safe place to do so is in the `__cinit__` and `__dealloc__` methods
which are guaranteed to be called exactly once upon creation and deletion of the Python
instance.
cdef class PyRectangle:
cdef Rectangle* c_rect # hold a pointer to the C++ instance which we're wrapping
def __cinit__(self, int x0, int y0, int x1, int y1):
self.c_rect = new Rectangle(x0, y0, x1, y1)
def __dealloc__(self):
del self.c_rect
...
If you prefer giving the same name to the wrapper as the C++ class, see the If you prefer giving the same name to the wrapper as the C++ class, see the
section on :ref:`resolving naming conflicts <resolve-conflicts>`. section on :ref:`resolving naming conflicts <resolve-conflicts>`.
......
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