Function pointer returning shared_ptr

[HGuillemet]

#include <memory>

struct S {
  int x;
};

std::shared_ptr<S> (*f)();

The JNI cannot compile with:

error: invalid conversion from 'std::shared_ptr<S> (*)()' to 'S* (*)()' [-fpermissive]
  628 |     if (rptr != NULL) rptr->ptr = f;

Because the generated class:

struct JavaCPP_hidden JavaCPP_j_S_1F {
    JavaCPP_j_S_1F() : ptr(NULL), obj(NULL) { }
    S* operator()();
    S* (*ptr)();
    jobject obj; static jmethodID mid;
};

has a function returning S* instead of std::shared_ptr<S>.

[saudet]

JavaCPP needs a FunctionPointer peer class

[HGuillemet]

Sure. The problem, if I understood well, is the @SharedPtr annotation not taken into account by the Generator when generating the peer class.

[saudet]

Right, so where is that FunctionPointer class?

[HGuillemet]

@Properties(inherit = presets.P.class)
public class S_F extends FunctionPointer {
    static { Loader.load(); }
    /** Pointer cast constructor. Invokes {@link Pointer#Pointer(Pointer)}. */
    public    S_F(Pointer p) { super(p); }
    protected S_F() { allocate(); }
    private native void allocate();
    public native @SharedPtr S call();
}

That's the class automatically generated by the parser from the C++ code above.

[saudet]

You'll need to add at least a @Cast to that...

[HGuillemet]

public native @Cast({"", "std::shared_ptr<S>"}) @SharedPtr S call();

seems to work. Thanks.

Do we close this issue or keep it open in case there is something to fix to avoid this @Cast ?

[saudet]

We need to specify the type somehow. As I've mentioned somewhere before, think of @Cast as if it were named @As instead.

[HGuillemet]

@SharedPtr already means that the function returns a shared_ptr of S. For a normal function, that calls a native function of the object pointed by the Pointer instead of the native function directly pointed by the Pointer, we don't need the @Cast.

[saudet]

No, it doesn't, for example, see issue #717

[HGuillemet]

In #717 the @Cast is to disambiguate between 2 overloads of unique_ptr.operator=. The @Cast doesn't change the type of the field.