Prototype for a scheme for upb Rust wrappers for upb.

upbwrapper.rs

// Prototype for a scheme for upb Rust wrappers for upb.
//
// Output (when linked with fakeupb.c):
//   C: new()
//   C: number() = 1
//   Number: 1
//   C: setnumber(5)
//   C: number() = 5
//   Number: 5
//   C: freeze() = 1
//   C: ref() = 1 -> 2
//   C: unref() = 2 -> 1
//   C: number() = 5
//   Number: 5
//   C: unref() = 1 -> 0

struct FieldDef;

#[link(name = "fakeupb")]
extern {
  fn upb_fielddef_setnumber(f: *mut FieldDef, number: u32) -> bool;
  fn upb_fielddef_number(f: *FieldDef) -> u32;
  fn upb_fielddef_new() -> *FieldDef;
  fn upb_fielddef_ref(f: *FieldDef);
  fn upb_fielddef_unref(f: *FieldDef);
  fn upb_fielddef_freeze(f: *FieldDef);
}


/****************************************************************************
 * FieldDefFrozenRef
 ****************************************************************************/

struct FieldDefFrozenRef {
  priv ptr: *FieldDef,
}

impl FieldDefFrozenRef {
  fn get<'a>(&'a self) -> &'a FieldDef {
    unsafe { &*self.ptr }
  }
}

impl Clone for FieldDefFrozenRef {
  fn clone(&self) -> FieldDefFrozenRef {
    unsafe { upb_fielddef_ref(self.ptr); }
    FieldDefFrozenRef { ptr: self.ptr }
  }
}

impl Drop for FieldDefFrozenRef {
  fn drop(&mut self) {
    unsafe { upb_fielddef_unref(self.ptr); }
  }
}

/****************************************************************************
 * FieldDefMutableRef
 ****************************************************************************/

struct FieldDefMutableRef {
  priv ptr: *FieldDef,
}

impl FieldDefMutableRef {
  fn get<'a>(&'a self) -> &'a mut FieldDef {
    unsafe { std::cast::transmute_mut(&*self.ptr) }
  }

  fn freeze(self) -> FieldDefFrozenRef {
    unsafe {
      upb_fielddef_freeze(self.ptr);
      upb_fielddef_ref(self.ptr);
    }
    FieldDefFrozenRef { ptr: self.ptr }
  }
}

impl Drop for FieldDefMutableRef {
  fn drop(&mut self) {
    unsafe { upb_fielddef_unref(self.ptr); }
  }
}

// No Clone because the mutable ref should never be cloned.

/****************************************************************************
 * FieldDef
 ****************************************************************************/

impl FieldDef {
  fn new() -> FieldDefMutableRef {
    let f: *FieldDef = unsafe { upb_fielddef_new() };
    FieldDefMutableRef { ptr: f }
  }
  fn set_number(&mut self, number: u32) -> bool {
    unsafe { upb_fielddef_setnumber(self, number) }
  }
  fn number(&self) -> u32 {
    unsafe { upb_fielddef_number(self) }
  }
}

fn main() {
  let mutable_def = FieldDef::new();
  std::io::println(format!("Number: {:u}", mutable_def.get().number()));
  mutable_def.get().set_number(5);
  std::io::println(format!("Number: {:u}", mutable_def.get().number()));
  let frozen_def = mutable_def.freeze();
  std::io::println(format!("Number: {:u}", frozen_def.get().number()));
}