Unable to use SharedPtr<T> to shared type

[mschuckmann]

I have some C++ code that needs to be able to construct and interact Rust objects that I can't add to the shared Rust interface. My solution has been to create a shim struct that is shared that holds a Boxed instance of the opaque Rust object. So I've defined shared structure and function like so:

#[cxx::bridge(namespace = "test")]
mod ffi {

    extern "Rust" {
        type RustFoo;

        struct CppFoo {
            inner: Box<RustFoo>,
        }

        fn new_Foo() -> UniquePtr<CppFoo>;
        fn do_something(self: &CppFoo); 
    }  
}

impl ffi::CppFoo {
   pub fn do_something(&self) {
      self.inner.something();  
   }
}

fn new_Foo() -> UniquePtr<ffi::CppFoo> {
  let t = ffi::CppFoo { inner: Box::new(RustFoo::new()) };
  return UniquePtr::new(t);
}

This all works with UniquePtr but with SharedPtr I get the error:

fn new_Foo() -> SharedPtr<ffi::CppFoo> {
    |                                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `SharedPtrTarget` is not implemented for `CppFoo`

What am I doing missing or doing wrong? Or am I going about this the wrong way?

[dtolnay]

You need to add impl SharedPtr<CppFoo> {} inside the ffi module that defines CppFoo in order for SharedPtr<CppFoo> to work, if SharedPtr<CppFoo> isn't otherwise already mentioned in that module.

See https://cxx.rs/extern-c++.html#explicit-shim-trait-impls.

[mschuckmann]

Thank you helped but now I'm getting a linker error when I try to link the generated .a library with the .so I'm creating.

The error looks something like this, I think it's saying that the rust .a library needs to be recompiled with -fPIC but I'm not sure how to do that with Rust.

relocation R_X86_64_PC32 against symbol `_ZTVSt15_Sp_counted_ptrIPN9test14CppFooELN9__gnu_cxx12_Lock_policyE2EE' can not be used when making a shared object; recompile with -fPIC