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From: <rom...@us...> - 2006-08-10 06:38:49
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Revision: 390 Author: roman_yakovenko Date: 2006-08-09 23:38:41 -0700 (Wed, 09 Aug 2006) ViewCVS: http://svn.sourceforge.net/pygccxml/?rev=390&view=rev Log Message: ----------- adding answer to "How to automatically export template functions\\class?" Modified Paths: -------------- pyplusplus_dev/docs/documentation/how_to.rest Modified: pyplusplus_dev/docs/documentation/how_to.rest =================================================================== --- pyplusplus_dev/docs/documentation/how_to.rest 2006-08-09 12:50:32 UTC (rev 389) +++ pyplusplus_dev/docs/documentation/how_to.rest 2006-08-10 06:38:41 UTC (rev 390) @@ -128,6 +128,124 @@ For more information, please read the documentation. +------------------------------------------------------ +How to automatically export template functions\\class? +------------------------------------------------------ + +Lets say you have next C++ function: +:: + + //file point.h + +:: + + namespace geometry{ + +:: + + template< class T> + struct point_t{ + T x, y; + }; + +:: + + template <class T> + double distance( const point_t<T>& point ){ + return sqrt( point.x * point.x + point.y*point.y ); + } + +:: + + } //namespace geometry + + +You should understand, that you can not export template itself, but only its +instantiations. The solution is built using next facts: + +* ``sizeof( class name )`` causes a compiler to instantiate the class + +* free function invocation causes a compiler to instantiate the function + +Lets say that we need to exprort the class and the function template +instantiations for ``int`` and ``cutom_type`` types. There are few ways to do it. + +Simple and straightforward +-------------------------- + +Open your favorite editor and create a header file with the content: + +:: + + #include "point.h" + +:: + + namespace py_details{ + inline void instantiate(){ + using namespace geometry; + sizeof( point_t<int> ); + sizeof( point_t<cutom_type> ); + distance( point_t<int>(0,0) ); + distance( point_t<cutom_type>(0,0) ); + } + } + +Now, you add this file to the list of files you pass as input to +``module_builder_t.__init__`` method and excludes the ``py_details`` namespace +declarations from being exported: + +:: + + mb = module_builder_t( [..., just created file ], ... ) + mb.namespace( 'py_details' ).exclude() + +"Dynamic" instantiation +----------------------- + +Lets say you are less lucky than I, and you have to create ``X`` instantiations +of the class\\function. Obviously, the previous approach will not work for you. +The solution is to build your own code generator, that will generate code similar +to the one, in the previous paragragh. + +:: + + from module_builder import module_builder_t, create_text_fc + +:: + + def generate_instantiations_string( ... ): + ... + +:: + + code = generate_instantiations_string( ... ) + +:: + + mb = module_builder_t( [ ..., create_text_fc( code ) ], ... ) + mb.namespace( 'py_details' ).exclude() + + +`pyplusplus`_ allows you to extract declarations from string, that contains +valid C++ code. It creates temporal header file and compiles it. At the end of +the compilation process it will remove it. You can read mode about ``create_text_fc`` +function `here`__. + +.. __ : ./../../pygccxml/design.html#parser-configuration-classes + + + +I understand that the provided solution is not perfect. I understand that something +better and simpler should be done, but a priority of this is low. There are few +tasks, that have much higher priority. Allen Bierbaum wants to fix the situation. +He created a `wiki page`_, that discuss possible solutions. Your contribution is +welcome too! + +.. _`wiki page` : https://realityforge.vrsource.org/view/PyppApi/TemplateSupport + + + .. _`pyplusplus` : ./../pyplusplus.html .. _`boost.python`: http://www.boost.org/libs/python/doc/index.html .. _`Python`: http://www.python.org This was sent by the SourceForge.net collaborative development platform, the world's largest Open Source development site. |
