opencv/interfaces/swig/python/cvswigmacros.i

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/* This file contains swig macros that are used in several typemap files */


%define %myshadow(function)
%ignore function;
%rename (function) function##_Shadow;
%enddef

// Elsewhere in this wrapper, the cvRelease* functions are mapped to 
// the destructors for the corresponding OpenCV object wrapper.  This
// is done in order to let Python handle memory management.  If the 
// reference count of the Python object wrapping the OpenCV object 
// goes to 0, the garbage collector will call the destructor, and 
// therefore the cvRelease* function, before freeing the Python object.
// However, if the user explicitly calls the cvRelease* function, we 
// must prevent the Python garbage collector from calling it again when
// the refcount reaches 0 -- otherwise a double-free error occurs.
//
// Thus, below, we redirect each cvRelease* function to the 
// corresponding OpenCV object's destructor.  This has the effect of:
// (1) Calling the corresponding cvRelease* function, and therefore 
//     immediately releasing the OpenCV object.
// (2) Telling SWIG to disown memory management for this OpenCV object.  
//
// Thus, when the refcount for the Python object reaches 0, the Python
// object is garbage collected, but since it no longer owns the OpenCV 
// object, this is not freed again.
%define %myrelease(module, Function, Type)
%ignore Function;
%rename (Function) Function##_Shadow;
%pythoncode %{
Function = _##module##.delete_##Type
%}
%enddef