commit 9bffb93783035dcdc073d562fc23d5f33f913751
author David Tolnay <dtolnay@gmail.com> Sat Jan 02 02:15:21 2021 -0800
committer David Tolnay <dtolnay@gmail.com> Sat Jan 02 15:01:59 2021 -0800
tree 840d5ef0f8f3d645bbe37a88c69d5f14ae8acbf3
parent 2a58a8afdf2b9fabcc9721dd598b7c7f9f011dbe

Preserve &[T]'s Rust representation in rust::Slice

include/cxx.h

diff --git a/include/cxx.h b/include/cxx.h
index 03f719f..a81fc21 100644
--- a/include/cxx.h
+++ b/include/cxx.h
@@ -180,10 +180,9 @@
   void swap(Slice &) noexcept;
 
 private:
-  // Not necessarily ABI compatible with &[T]. Codegen will translate to
-  // cxx::rust_slice::RustSlice which matches this layout.
-  void *ptr;
-  std::size_t len;
+  void *ptr() const noexcept;
+
+  std::array<std::uintptr_t, 2> repr;
 };
 
 template <typename T>
@@ -489,37 +488,42 @@
 #ifndef CXXBRIDGE1_RUST_SLICE
 #define CXXBRIDGE1_RUST_SLICE
 template <typename T>
-Slice<T>::Slice() noexcept
-    : ptr(reinterpret_cast<void *>(align_of<T>())), len(0) {}
+Slice<T>::Slice() noexcept {
+  void sliceInit(void *, const void *, std::size_t) noexcept;
+  sliceInit(this, reinterpret_cast<void *>(align_of<T>()), 0);
+}
 
 template <typename T>
-Slice<T>::Slice(T *s, std::size_t count) noexcept
-    : ptr(const_cast<typename std::remove_const<T>::type *>(s)), len(count) {}
+Slice<T>::Slice(T *s, std::size_t count) noexcept {
+  void sliceInit(void *, const void *, std::size_t) noexcept;
+  sliceInit(this, const_cast<typename std::remove_const<T>::type *>(s), count);
+}
 
 template <typename T>
 T *Slice<T>::data() const noexcept {
-  return reinterpret_cast<T *>(this->ptr);
+  return reinterpret_cast<T *>(this->ptr());
 }
 
 template <typename T>
 std::size_t Slice<T>::size() const noexcept {
-  return this->len;
+  std::size_t sliceLen(const void *) noexcept;
+  return sliceLen(this);
 }
 
 template <typename T>
 std::size_t Slice<T>::length() const noexcept {
-  return this->len;
+  return this->size();
 }
 
 template <typename T>
 bool Slice<T>::empty() const noexcept {
-  return this->len == 0;
+  return this->size() == 0;
 }
 
 template <typename T>
 T &Slice<T>::operator[](std::size_t n) const noexcept {
   assert(n < this->size());
-  auto pos = static_cast<char *>(this->ptr) + size_of<T>() * n;
+  auto pos = static_cast<char *>(this->ptr()) + size_of<T>() * n;
   return *reinterpret_cast<T *>(pos);
 }
 
@@ -540,7 +544,7 @@
 template <typename T>
 T &Slice<T>::back() const noexcept {
   assert(!this->empty());
-  return (*this)[this->len - 1];
+  return (*this)[this->size() - 1];
 }
 
 template <typename T>
@@ -659,7 +663,7 @@
 template <typename T>
 typename Slice<T>::iterator Slice<T>::begin() const noexcept {
   iterator it;
-  it.pos = this->ptr;
+  it.pos = this->ptr();
   it.stride = size_of<T>();
   return it;
 }
@@ -667,7 +671,7 @@
 template <typename T>
 typename Slice<T>::iterator Slice<T>::end() const noexcept {
   iterator it = this->begin();
-  it.pos = static_cast<char *>(it.pos) + it.stride * this->len;
+  it.pos = static_cast<char *>(it.pos) + it.stride * this->size();
   return it;
 }
 
@@ -675,6 +679,12 @@
 void Slice<T>::swap(Slice &rhs) noexcept {
   std::swap(*this, rhs);
 }
+
+template <typename T>
+void *Slice<T>::ptr() const noexcept {
+  void *slicePtr(const void *) noexcept;
+  return slicePtr(this);
+}
 #endif // CXXBRIDGE1_RUST_SLICE
 
 #ifndef CXXBRIDGE1_RUST_BOX