Add Gc::as_ptr

gc/src/lib.rs

@@ -110,6 +110,24 @@ impl<T: ?Sized> Gc<T> {
     pub fn ptr_eq(this: &Gc<T>, other: &Gc<T>) -> bool {
         GcBox::ptr_eq(this.inner(), other.inner())
     }
+
+    /// Provides a raw pointer to the data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use gc::Gc;
+    ///
+    /// let x = Gc::new("hello".to_owned());
+    /// let y = x.clone();
+    /// let x_ptr = Gc::as_ptr(&x);
+    /// assert_eq!(x_ptr, Gc::as_ptr(&y));
+    /// assert_eq!(unsafe { &*x_ptr }, "hello");
+    /// ```
+    pub fn as_ptr(this: &Gc<T>) -> *const T {
+        let ptr = this.inner_ptr();
+        GcBox::value_ptr(ptr)
+    }
 }
 
 /// Returns the given pointer with its root bit cleared.

gc/tests/gc_semantics.rs

@@ -289,3 +289,31 @@ fn ptr_eq() {
     assert!(!Gc::ptr_eq(&b.0, &b2.0));
     assert!(!Gc::ptr_eq(&b.0, &a2));
 }
+
+#[test]
+fn as_ptr() {
+    #[derive(Finalize, Trace)]
+    struct A;
+
+    #[derive(Finalize, Trace)]
+    struct B(Gc<A>);
+
+    let a = Gc::new(A);
+    let aa = a.clone();
+    let a_ptr = Gc::as_ptr(&a);
+    assert_eq!(a_ptr, Gc::as_ptr(&aa));
+
+    let b =  Gc::new(B(a.clone()));
+    assert_eq!(a_ptr, Gc::as_ptr(&b.0));
+    let bb = Gc::new(B(a.clone()));
+    assert_eq!(a_ptr, Gc::as_ptr(&bb.0));
+
+    let a2 = Gc::new(A);
+    let a2_ptr = Gc::as_ptr(&a2);
+    assert_ne!(a_ptr, a2_ptr);
+    let b2 = Gc::new(B(a2.clone()));
+    assert_eq!(a2_ptr, Gc::as_ptr(&b2.0));
+    assert_ne!(a_ptr, Gc::as_ptr(&b2.0));
+    assert_ne!(Gc::as_ptr(&b.0), Gc::as_ptr(&b2.0));
+    assert_ne!(Gc::as_ptr(&b.0), a2_ptr);
+}