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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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Lib/python/pyopers.swg
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@ -151,11 +151,11 @@ __bool__ = __nonzero__
They translate the inplace C++ operators (+=, -=, ...) into the They translate the inplace C++ operators (+=, -=, ...) into the
corresponding python equivalents(__iadd__,__isub__), etc, 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: it to the returning object:
%feature("del") *::Operator; %feature("del") *::Operator; // disables ownership by generating SWIG_POINTER_DISOWN
%feature("new") *::Operator; %feature("new") *::Operator; // claims ownership by generating SWIG_POINTER_OWN
This makes the most common case safe, ie: 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 that never get deleted (maybe, not sure, it depends). But if that is
the case, you could recover the old behaviour using the case, you could recover the old behaviour using
%feature("del","") A::operator+=; %feature("del","0") A::operator+=;
%feature("new","") A::operator+=; %feature("new","0") A::operator+=;
which recovers the old behaviour for the class 'A', or if you are 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: 100% sure your entire system works fine in the old way, use:
@ -183,6 +183,12 @@ __bool__ = __nonzero__
%feature("del","") *::operator+=; %feature("del","") *::operator+=;
%feature("new","") *::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) #if defined(SWIGPYTHON_BUILTIN)