shared_ptr and directors.

[Andrea-60]

I would like to ask some help about the use of directors for virtual functions that return a shared_ptr.

This is a self contained example: compiled with swig -c++ -java a.i

The key method is A::b() which returns a boost_shared_ptr<A>.
I would like to subclass A in Java so that this function is entirely implemented in Java.
The class B does not have any problem.

When I look at the code created for A::b() in Java I see

class A {
   public BPtr b() {
     return new BPtr(aJNI.A_b(swigCPtr, this), true);
   }
}

If I wanted to create a subclass of A, I would have to implement a new method b() returning a BPtr.
But there is no way to create a BPtr from a class inheriting from B.
I was expecting a method in BPtr returning a B, but there isn't.

Everything works very well if I change my functions to return raw pointers rather than shared_ptr.

Any idea?

%module (directors="1") a

%include "shared_ptr.i"

class B
{
  public:
   virtual double value() = 0;
   virtual ~B() {}
};

class A
{
  public:
   virtual boost::shared_ptr<B> b() = 0;
   virtual ~A() {}
};

class B1 : public B
{
  public:
   virtual double value() {return 1.0;}
};

class A1 : public A
{
  public:
   virtual boost::shared_ptr<B> b()
     {
       return boost::shared_ptr<B>(new B1());
     }
};

double foo(A * a)
{
   return a->b()->value();
}


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[Andrea-60]

On 21/10/09 11:18, Andrea wrote:

> I would like to ask some help about the use of directors for virtual functions that return a shared_ptr.
>
> This is a self contained example: compiled with swig -c++ -java a.i
>
> The key method is A::b() which returns a boost_shared_ptr<A>.
> I would like to subclass A in Java so that this function is entirely implemented in Java.
> The class B does not have any problem.
>
> When I look at the code created for A::b() in Java I see
>
> class A {
>     public BPtr b() {
>       return new BPtr(aJNI.A_b(swigCPtr, this), true);
>     }
> }
>
> If I wanted to create a subclass of A, I would have to implement a new method b() returning a BPtr.
> But there is no way to create a BPtr from a class inheriting from B.
> I was expecting a method in BPtr returning a B, but there isn't.
>
> Everything works very well if I change my functions to return raw pointers rather than shared_ptr.

I've found a workaround.
Basically what is missing is a function like (in Java)

BPtr transformB(B b);

which can be easily added to the c++ file as

boost::shared_ptr<B> transformB(B * b)
{
   return boost::shared_ptr<B>(b);
}

then I can write

class MyA {
      public BPtr b() {
        return transformB(new MyB());
      }
}

my question then is: why the shared_ptr<B> does not expose a constructor that takes a B
(i.e. a B * in C++)?


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[Andrea-60]

On 21/10/09 12:50, Andrea wrote:

> On 21/10/09 11:18, Andrea wrote:
> I've found a workaround.
> Basically what is missing is a function like (in Java)
>
> BPtr transformB(B b);
>
> which can be easily added to the c++ file as
>
> boost::shared_ptr<B>  transformB(B * b)
> {
>     return boost::shared_ptr<B>(b);
> }
>

I am not too sure any more about that.
Is the memory ownership ok?

> then I can write
>
> class MyA {
>        public BPtr b() {
>          return transformB(new MyB());
>        }
> }
>
> my question then is: why the shared_ptr<B>  does not expose a constructor that takes a B
> (i.e. a B * in C++)?

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[wsfulton]

Andrea wrote:
> I would like to ask some help about the use of directors for virtual functions that return a shared_ptr.
>
> This is a self contained example: compiled with swig -c++ -java a.i
>
> The key method is A::b() which returns a boost_shared_ptr<A>.
> I would like to subclass A in Java so that this function is entirely implemented in Java.
> The class B does not have any problem.
>
Andrea,

There is currently no support for shared_ptr and the directors feature.
The director typemaps need to be written in order to support this. These
typemaps are: directorin, directorout, javadirectorin, javadirectorout.

William

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[Andrea-60]

On 27/10/09 07:38, William S Fulton wrote:

> Andrea wrote:
>> I would like to ask some help about the use of directors for virtual functions that return a shared_ptr.
>>
>> This is a self contained example: compiled with swig -c++ -java a.i
>>
>> The key method is A::b() which returns a boost_shared_ptr<A>.
>> I would like to subclass A in Java so that this function is entirely implemented in Java.
>> The class B does not have any problem.
>>
> Andrea,
>
> There is currently no support for shared_ptr and the directors feature.
> The director typemaps need to be written in order to support this. These
> typemaps are: directorin, directorout, javadirectorin, javadirectorout.

On the other hand if I return a raw pointer I get a warning

" Returning a pointer or reference in a director method is not recommended. "

Does it mean that in directors I can only return by value?


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[wsfulton]

Andrea wrote:

> On 27/10/09 07:38, William S Fulton wrote:
>> Andrea wrote:
>>> I would like to ask some help about the use of directors for virtual functions that return a shared_ptr.
>>>
>>> This is a self contained example: compiled with swig -c++ -java a.i
>>>
>>> The key method is A::b() which returns a boost_shared_ptr<A>.
>>> I would like to subclass A in Java so that this function is entirely implemented in Java.
>>> The class B does not have any problem.
>>>
>> Andrea,
>>
>> There is currently no support for shared_ptr and the directors feature.
>> The director typemaps need to be written in order to support this. These
>> typemaps are: directorin, directorout, javadirectorin, javadirectorout.
>
> On the other hand if I return a raw pointer I get a warning
>
> " Returning a pointer or reference in a director method is not recommended. "
>
> Does it mean that in directors I can only return by value?
>

Take a close look at the generated code with pointers and you'll see the
memory complications, with no clear solution. However, I very much doubt
these problems would exist if you used shared_ptr and the director
typemaps for shared_ptr were written.

William

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[Andrea-60]

On 01/11/09 21:03, William S Fulton wrote:

>>
>> On the other hand if I return a raw pointer I get a warning
>>
>> " Returning a pointer or reference in a director method is not recommended. "
>>
>> Does it mean that in directors I can only return by value?
>>
> Take a close look at the generated code with pointers and you'll see the
> memory complications, with no clear solution. However, I very much doubt
> these problems would exist if you used shared_ptr and the director
> typemaps for shared_ptr were written.

I've written typemaps for customized types, but never for directors.
If you could give some hints about problems/solutions, you would make my life a lot easier.

Andrea


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