Expose capacity and reserve on rust::String

book/src/binding/string.md

@@ -40,6 +40,9 @@ public:
 
   const char *c_str() noexcept;
 
+  size_t capacity() const noexcept;
+  void reserve(size_t new_cap) noexcept;
+
   using iterator = char *;
   iterator begin() noexcept;
   iterator end() noexcept;

include/cxx.h

@@ -59,6 +59,9 @@ class String final {
 
   const char *c_str() noexcept;
 
+  std::size_t capacity() const noexcept;
+  void reserve(size_t new_cap) noexcept;
+
   using iterator = char *;
   iterator begin() noexcept;
   iterator end() noexcept;

src/cxx.cc

@@ -40,8 +40,11 @@ bool cxxbridge1$string$from_utf16(rust::String *self, const char16_t *ptr,
 void cxxbridge1$string$drop(rust::String *self) noexcept;
 const char *cxxbridge1$string$ptr(const rust::String *self) noexcept;
 std::size_t cxxbridge1$string$len(const rust::String *self) noexcept;
+std::size_t cxxbridge1$string$capacity(const rust::String *self) noexcept;
 void cxxbridge1$string$reserve_additional(rust::String *self,
                                           size_t additional) noexcept;
+void cxxbridge1$string$reserve_total(rust::String *self,
+                                     size_t new_cap) noexcept;
 
 // rust::Str
 void cxxbridge1$str$new(rust::Str *self) noexcept;
@@ -165,6 +168,14 @@ const char *String::c_str() noexcept {
   return ptr;
 }
 
+std::size_t String::capacity() const noexcept {
+  return cxxbridge1$string$capacity(this);
+}
+
+void String::reserve(std::size_t new_cap) noexcept {
+  cxxbridge1$string$reserve_total(this, new_cap);
+}
+
 String::iterator String::begin() noexcept {
   return const_cast<char *>(this->data());
 }

src/symbols/rust_string.rs

@@ -69,7 +69,20 @@ unsafe extern "C" fn string_len(this: &String) -> usize {
     this.len()
 }
 
+#[export_name = "cxxbridge1$string$capacity"]
+unsafe extern "C" fn string_capacity(this: &String) -> usize {
+    this.capacity()
+}
+
 #[export_name = "cxxbridge1$string$reserve_additional"]
 unsafe extern "C" fn string_reserve_additional(this: &mut String, additional: usize) {
     this.reserve(additional);
 }
+
+#[export_name = "cxxbridge1$string$reserve_total"]
+unsafe extern "C" fn string_reserve_total(this: &mut String, new_cap: usize) {
+    if new_cap > this.capacity() {
+        let additional = new_cap - this.len();
+        this.reserve(additional);
+    }
+}

tests/ffi/tests.cc

@@ -835,6 +835,12 @@ extern "C" const char *cxx_run_test() noexcept {
   ASSERT(cstring == "foo");
   ASSERT(other_cstring == "test");
 
+  ASSERT(cstring.capacity() == 3);
+  cstring.reserve(2);
+  ASSERT(cstring.capacity() == 3);
+  cstring.reserve(5);
+  ASSERT(cstring.capacity() >= 5);
+
   rust::Str cstr = "test";
   rust::Str other_cstr = "foo";
   swap(cstr, other_cstr);