[boost] Re : Re : Using an element of a class A in a constructor of a class B (reflection with boost::python)

Subject: [boost] Re : Re : Using an element of a class A in a constructor of a class B (reflection with boost::python)
From: christophe jean-joseph (jjchristophe_at_[hidden])
Date: 2012-03-12 08:24:55

Thank you very much for the answers.
@Steven Watanabe.

Sorry, I should have been more clear by showing the solution I found for a non constructor.
Let's say I have B::Foo(A& a){} (where foo isn't a ctor of B)

I reflect it as follow:

class_A <A, boost::noncopyable>("A", no_init)  //this line can be modified

    .def("Foo", &B::Foo);
class_B <B, boost::noncopyable>("B", init< >())  //this line can be modified
    .def("Foo", &B::Foo);

Meanning I have to declare Foo in both A and B for boost:;python.
My problem is that I can't do the same for a ctor.


@Jim Bosch

thank you for your advices. As I am new with boost, and with the mailing list, I didn't know where I should ask my question. I will try my luck there.

Christophe Jean-Joseph

 


________________________________
 De : Jim Bosch <talljimbo_at_[hidden]>
À : boost_at_[hidden] 
Cc : christophe jean-joseph <jjchristophe_at_[hidden]> 
Envoyé le : Dimanche 11 mars 2012 4h37
Objet : Re: [boost] Re : Using an element of a class A in a constructor of a class B (reflection with boost::python)
 

On 03/10/2012 09:32 PM, christophe jean-joseph wrote:
> 
> 
> Thank you for your message, but it does not answer my question, I know how to reflect a C++ constructor under Python through boost and have absolutly no problem with that.
> My question is about reflecting Bctor(A&  a, double&  x) where Bctor is the constructor of class B and A another class.
> As I said, I can do that for any other function, except a constructor.
> I already read many website, including python and boost websites, before asking my question here.
> The link you provided, and that I already read before, only explain how to reflect a constructor.
> That would be of great help if anyone could give me some clue.
> 

If the "double &" argument is intended to return a value, then I'm afraid you're pretty much stuck, unless you're willing to put the value in some kind of mutable proxy object (e.g. a one-element list).  Python floats are immutable, so they simply can't be used as output arguments.  And since constructors can't return values, you can't just change the signature.  That's a Python limitation, not a Boost.Python one.

If you don't care about the value of the "double &" argument after the call, you can just pretend that it's passed by value, i.e.:

namespace bp = boost::python;

bp::class_<B>("B")
    .def(bp::init<A&,double>())
    ;

By the way, you'll probably get more attention on Boost.Python questions on the cplusplus-sig_at_[hidden] mailing list.

Jim