+ |
+ |
+ + Enums + | +
 |
+  |
+  |
+
+Boost.Python has a nifty facility to capture and wrap C++ enums. While +Python has no enum type, we'll often want to expose our C++ enums to +Python as an int. Boost.Python's enum facility makes this easy while +taking care of the proper conversions from Python's dynamic typing to C++'s +strong static typing (in C++, ints cannot be implicitly converted to +enums). To illustrate, given a C++ enum:
+
+ enum choice { red, blue };
+
+the construct:
+
+ enum_<choice>("choice")
+ .value("red", red)
+ .value("blue", blue)
+ ;
+
+can be used to expose to Python. The new enum type is created in the +current scope(), which is usually the current module. The snippet above +creates a Python class derived from Python's int type which is +associated with the C++ type passed as its first parameter.
+
+ what is a scope?The scope is a class that has an +associated global Python object which controls the Python namespace in +which new extension classes and wrapped functions will be defined as +attributes. Details can be found +here. |
+
+You can access those values in Python as
+
+ >>> my_module.choice.red
+ my_module.choice.red
+
+where my_module is the module where the enum is declared. You can also +create a new scope around a class:
+
+ scope in_X(class_<X>("X")
+ .def( ... )
+ .def( ... )
+ );
+
+ // Expose X::nested as X.nested
+ enum_<X::nested>("nested")
+ .value("red", red)
+ .value("blue", blue)
+ ;
+
|
+ |
+ |
+
Copyright © 2002 David Abrahams
Copyright © 2002 Joel de Guzman
+Permission to copy, use, modify, sell and distribute this document
+ is granted provided this copyright notice appears in all copies. This document
+ is provided "as is" without express or implied warranty, and with
+ no claim as to its suitability for any purpose.