On 3 October 2014 18:23, Jim Bosch <tallji...@gmail.com> wrote:
> On Fri, Oct 3, 2014 at 1:15 PM, Stefan Seefeld <ste...@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
>
> Not quite. get_property's 4th argument is just a docstring.
It seems only def has a policy argument.
Actually this is a problem because the next 2 properties of the class are
big vectors.
I am gonna go with just defs of getter/setter instead as add_property
doesn't help (i looked at class.hpp inside boost.python)
MM
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