Add begin/end iterators to rust::Vec

gen/write.rs

@@ -147,6 +147,7 @@ fn write_include_cxxbridge(out: &mut OutFile, apis: &[Api], types: &Types) {
             }
             Type::RustVec(_) => {
                 out.include.array = true;
+                out.include.type_traits = true;
                 needs_rust_vec = true;
             }
             Type::Str(_) => {

include/cxx.h

@@ -205,12 +205,50 @@ private:
 template <typename T>
 class Vec final {
 public:
+  using value_type = T;
+
   ~Vec() noexcept { this->drop(); }
 
   size_t size() const noexcept;
   bool empty() const noexcept { return size() == 0; }
   const T *data() const noexcept;
 
+  class const_iterator {
+  public:
+    using value_type = typename std::add_const<T>::type;
+    using reference = typename std::add_lvalue_reference<
+        typename std::add_const<T>::type>::type;
+
+    const T &operator*() const { return *static_cast<const T *>(this->pos); }
+    const_iterator &operator++() {
+      this->pos = static_cast<const uint8_t *>(this->pos) + this->stride;
+      return *this;
+    }
+    bool operator==(const const_iterator &other) const {
+      return this->pos == other.pos;
+    }
+    bool operator!=(const const_iterator &other) const {
+      return this->pos != other.pos;
+    }
+
+  private:
+    friend class Vec;
+    const void *pos;
+    size_t stride;
+  };
+
+  const_iterator begin() const noexcept {
+    const_iterator it;
+    it.pos = this->data();
+    it.stride = this->stride();
+    return it;
+  }
+  const_iterator end() const noexcept {
+    const_iterator it = this->begin();
+    it.pos = static_cast<const uint8_t *>(it.pos) + it.stride * this->size();
+    return it;
+  }
+
 private:
   static size_t stride() noexcept;
   void drop() noexcept;

tests/ffi/tests.cc

@@ -163,17 +163,15 @@ void c_take_unique_ptr_vector_shared(std::unique_ptr<std::vector<Shared>> v) {
 }
 
 void c_take_vec_u8(const rust::Vec<uint8_t> &v) {
-  auto cv = static_cast<std::vector<uint8_t>>(v);
-  uint8_t sum = std::accumulate(cv.begin(), cv.end(), 0);
+  uint8_t sum = std::accumulate(v.begin(), v.end(), 0);
   if (sum == 200) {
     cxx_test_suite_set_correct();
   }
 }
 
 void c_take_vec_shared(const rust::Vec<Shared> &v) {
-  auto cv = static_cast<std::vector<Shared>>(v);
   uint32_t sum = 0;
-  for (auto i : cv) {
+  for (auto i : v) {
     sum += i.z;
   }
   if (sum == 2021) {