On Thursday, 10 October 2013 at 23:02:29 UTC, Timothee Cour wrote:
Short version:
I have a struct A* aptr allocated in C/C++ with an internal
pointer aptr->ptr (say a double*)
I want to store a reference x (say double[]) in D to aptr only
through
aptr->ptr, not through aptr directly as it's inconvenient in my
use case.
How do I achieve that, so that when x goes out of scope, some
deallocator
for aptr will be called ?
Long version:
----
suppose I have C++ code:
struct A{
double*ptr;
A(size_t n){ptr=(double*)malloc(n);}
~A(){free(ptr);}
};
and a D wrapper around it:
extern(C){struct A; A*A_new(size_t n); void A_delete(A*a);
double*A_ptr(A*a);}
I want to use it as follows:
double[] get_x(size_t n){
return A_new(n).A_ptr[0..n];
}
void main(){
double[]x=get_x(n);
// do something with x;
}
----
It's trivial to handle this via a class wrapper:
class A2{
A*a;
this(size_t n){a=A_new(n);}
~this(){A_delete(n);}
double*ptr(){return A_ptr(a);}
}
double[] get_x(size_t n){
auto a2=new A2(n);
return a2.ptr;
//this doesn't help much though, A2 will go out of scope when
this function
exits.
}
but I don't want to maintain objects of class A2 around, just
double[]
slices as above.
Is there some magic involving core.memory.addRoot,addRange
(etc) I can use
so that a2 stays alive as long as x stays alive? (in which case
when x goes
out of scope, 'a2' will too, and will call A_delete).
Thanks
Ping?
Is anything above unclear?
here are more details (in a simplified setting):
say, I have an image class D_image which has fields:
ubyte* ptr //pointer to memory
uint[2] size;
I'd like to interface with, say, a swig-wrapped opencv C++ image
class Swig_image, so that when an object d_image:D_image goes out
of scope (and its pointer ptr also goes out of scope), (with
d_image constructed from an object swig_image of type
Swig_image), then swig_image will also go out of scope.
again, this can be done by adding a field to D_image (say of type
void* to make it work with any source), buy I'm wondering whether
this can be achieved without adding this field, with some GC
magic associating a pointer (ptr) to another pointer (cast(void*)
swig_image).
This would make interfacing with C++ libs much easier as there
would be no bookkeeping in user code.
