[C++-sig] boost python class member getter/setter same name different only by constness

[Jim Bosch]

On Fri, Oct 3, 2014 at 1:15 PM, Stefan Seefeld <stefan at seefeld.name> wrote:

> On 2014-10-03 12:56, MM wrote:
> > yes i did that.
> >
> >     class C {
> >     public:
> >       const std::string& get_name() const;
> >       void set_name(const std::string&);
> >     private:
> >       std::string name_;
> >     };
> >
> >
> >
> >     class_<C>("C").
> >       .add_property("name",   &C::get_name, &C::set_name);
> >
> >
> > this fails to compile because of unspecified call policies about the
> > string refs.
> >
> >
> > The following, on the other hand, compiles.
> >
> >     class C {
> >     public:
> >       const std::string get_name() const;
> >       void set_name(const std::string);
> >     ....
> >     class_<C>("C").
> >       .add_property("name",   &C::get_name, &C::set_name);
> >
> >
> > Which policy do I specify? and how do I set it in add_property?
>
> Good question. The policy you want is likely pass-by-value (In Python
> strings are immutable anyhow), however I have no idea how to express
> that with the add_property() call.
> As a quick hack I suggest adding a wrapper function that returns the
> result by-value:
>
>   std::string get_name(C &c) { return c.get_name();}
>
> and use that. That's neither elegant nor efficient (if you call it a
> lot), but it may unblock you until you find a real fix.
>
>
To use a call policy here, I *think* you'd pass
return_value_policy<return_by_value>() as the fourth argument to
add_property, but it may be some slight modification of that.  In any case,
I suspect that's no more efficient than Stefan's solution in this case.


Jim
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