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Add python inplace operator caveats to pyopers.swg

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Observations reported in issue #562
This commit is contained in:
William S Fulton 2015-12-05 19:23:14 +00:00
commit 625a405b8e
1 changed files with 11 additions and 5 deletions
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16
Lib/python/pyopers.swg
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@ -151,11 +151,11 @@ __bool__ = __nonzero__
They translate the inplace C++ operators (+=, -=, ...) into the
corresponding python equivalents(__iadd__,__isub__), etc,
disabling the ownership of the input 'self' pointer, and assigning
disabling the ownership of the input 'this' pointer, and assigning
it to the returning object:
%feature("del") *::Operator;
%feature("new") *::Operator;
%feature("del") *::Operator; // disables ownership by generating SWIG_POINTER_DISOWN
%feature("new") *::Operator; // claims ownership by generating SWIG_POINTER_OWN
This makes the most common case safe, ie:
@ -174,8 +174,8 @@ __bool__ = __nonzero__
that never get deleted (maybe, not sure, it depends). But if that is
the case, you could recover the old behaviour using
%feature("del","") A::operator+=;
%feature("new","") A::operator+=;
%feature("del","0") A::operator+=;
%feature("new","0") A::operator+=;
which recovers the old behaviour for the class 'A', or if you are
100% sure your entire system works fine in the old way, use:
@ -183,6 +183,12 @@ __bool__ = __nonzero__
%feature("del","") *::operator+=;
%feature("new","") *::operator+=;
The default behaviour assumes that the 'this' pointer's memory is
already owned by the SWIG object; it relinquishes ownership then
takes it back. This may not be the case though as the SWIG object
might be owned by memory managed elsewhere, eg after calling a
function that returns a C++ reference. In such case you will need
to use the features above to recover the old behaviour too.
*/
#if defined(SWIGPYTHON_BUILTIN)