Replace virtual dispatch with normal functions in buffers

include/fmt/core.h

@@ -8,12 +8,12 @@
 #ifndef FMT_CORE_H_
 #define FMT_CORE_H_
 
-#include <cstddef>  // std::byte
-#include <cstdio>   // std::FILE
-#include <cstring>  // std::strlen
-#include <iterator>
-#include <limits>
-#include <memory>  // std::addressof
+#include <cstddef>   // std::byte
+#include <cstdio>    // std::FILE
+#include <cstring>   // std::strlen
+#include <iterator>  // std::back_insert_iterator
+#include <limits>    // std::numeric_limits
+#include <memory>    // std::addressof
 #include <string>
 #include <type_traits>
 
@@ -821,13 +821,18 @@ template <typename T> class buffer {
   size_t size_;
   size_t capacity_;
 
+  using grow_fun = void (*)(buffer& buf, size_t capacity);
+  grow_fun grow_;
+
  protected:
   // Don't initialize ptr_ since it is not accessed to save a few cycles.
   FMT_MSC_WARNING(suppress : 26495)
-  FMT_CONSTEXPR buffer(size_t sz) noexcept : size_(sz), capacity_(sz) {}
+  FMT_CONSTEXPR buffer(grow_fun grow, size_t sz) noexcept
+      : size_(sz), capacity_(sz), grow_(grow) {}
 
-  FMT_CONSTEXPR20 buffer(T* p = nullptr, size_t sz = 0, size_t cap = 0) noexcept
-      : ptr_(p), size_(sz), capacity_(cap) {}
+  FMT_CONSTEXPR20 buffer(grow_fun grow, T* p = nullptr, size_t sz = 0,
+                         size_t cap = 0) noexcept
+      : ptr_(p), size_(sz), capacity_(cap), grow_(grow) {}
 
   FMT_CONSTEXPR20 ~buffer() = default;
   buffer(buffer&&) = default;
@@ -838,10 +843,6 @@ template <typename T> class buffer {
     capacity_ = buf_capacity;
   }
 
-  /** Increases the buffer capacity to hold at least *capacity* elements. */
-  // DEPRECATED!
-  virtual FMT_CONSTEXPR20 void grow(size_t capacity) = 0;
-
  public:
   using value_type = T;
   using const_reference = const T&;
@@ -880,7 +881,7 @@ template <typename T> class buffer {
   // for at least one additional element either by increasing the capacity or by
   // flushing the buffer if it is full.
   FMT_CONSTEXPR20 void try_reserve(size_t new_capacity) {
-    if (new_capacity > capacity_) grow(new_capacity);
+    if (new_capacity > capacity_) grow_(*this, new_capacity);
   }
 
   FMT_CONSTEXPR20 void push_back(const T& value) {
@@ -929,9 +930,8 @@ class iterator_buffer final : public Traits, public buffer<T> {
   enum { buffer_size = 256 };
   T data_[buffer_size];
 
- protected:
-  FMT_CONSTEXPR20 void grow(size_t) override {
-    if (this->size() == buffer_size) flush();
+  static FMT_CONSTEXPR20 void grow(buffer<T>& buf, size_t) {
+    if (buf.size() == buffer_size) static_cast<iterator_buffer&>(buf).flush();
   }
 
   void flush() {
@@ -942,9 +942,11 @@ class iterator_buffer final : public Traits, public buffer<T> {
 
  public:
   explicit iterator_buffer(OutputIt out, size_t n = buffer_size)
-      : Traits(n), buffer<T>(data_, 0, buffer_size), out_(out) {}
+      : Traits(n), buffer<T>(grow, data_, 0, buffer_size), out_(out) {}
   iterator_buffer(iterator_buffer&& other)
-      : Traits(other), buffer<T>(data_, 0, buffer_size), out_(other.out_) {}
+      : Traits(other),
+        buffer<T>(grow, data_, 0, buffer_size),
+        out_(other.out_) {}
   ~iterator_buffer() { flush(); }
 
   auto out() -> OutputIt {
@@ -963,9 +965,9 @@ class iterator_buffer<T*, T, fixed_buffer_traits> final
   enum { buffer_size = 256 };
   T data_[buffer_size];
 
- protected:
-  FMT_CONSTEXPR20 void grow(size_t) override {
-    if (this->size() == this->capacity()) flush();
+  static FMT_CONSTEXPR20 void grow(buffer<T>& buf, size_t) {
+    if (buf.size() == buf.capacity())
+      static_cast<iterator_buffer&>(buf).flush();
   }
 
   void flush() {
@@ -979,7 +981,7 @@ class iterator_buffer<T*, T, fixed_buffer_traits> final
 
  public:
   explicit iterator_buffer(T* out, size_t n = buffer_size)
-      : fixed_buffer_traits(n), buffer<T>(out, 0, n), out_(out) {}
+      : fixed_buffer_traits(n), buffer<T>(grow, out, 0, n), out_(out) {}
   iterator_buffer(iterator_buffer&& other)
       : fixed_buffer_traits(other),
         buffer<T>(std::move(other)),
@@ -1001,11 +1003,9 @@ class iterator_buffer<T*, T, fixed_buffer_traits> final
 };
 
 template <typename T> class iterator_buffer<T*, T> final : public buffer<T> {
- protected:
-  FMT_CONSTEXPR20 void grow(size_t) override {}
-
  public:
-  explicit iterator_buffer(T* out, size_t = 0) : buffer<T>(out, 0, ~size_t()) {}
+  explicit iterator_buffer(T* out, size_t = 0)
+      : buffer<T>([](buffer<T>&, size_t) {}, out, 0, ~size_t()) {}
 
   auto out() -> T* { return &*this->end(); }
 };
@@ -1017,17 +1017,18 @@ class iterator_buffer<std::back_insert_iterator<Container>,
                                   typename Container::value_type>>
     final : public buffer<typename Container::value_type> {
  private:
+  using value_type = typename Container::value_type;
   Container& container_;
 
- protected:
-  FMT_CONSTEXPR20 void grow(size_t capacity) override {
-    container_.resize(capacity);
-    this->set(&container_[0], capacity);
+  static FMT_CONSTEXPR20 void grow(buffer<value_type>& buf, size_t capacity) {
+    auto& self = static_cast<iterator_buffer&>(buf);
+    self.container_.resize(capacity);
+    self.set(&self.container_[0], capacity);
   }
 
  public:
   explicit iterator_buffer(Container& c)
-      : buffer<typename Container::value_type>(c.size()), container_(c) {}
+      : buffer<value_type>(grow, c.size()), container_(c) {}
   explicit iterator_buffer(std::back_insert_iterator<Container> out, size_t = 0)
       : iterator_buffer(get_container(out)) {}
 
@@ -1043,15 +1044,14 @@ template <typename T = char> class counting_buffer final : public buffer<T> {
   T data_[buffer_size];
   size_t count_ = 0;
 
- protected:
-  FMT_CONSTEXPR20 void grow(size_t) override {
-    if (this->size() != buffer_size) return;
-    count_ += this->size();
-    this->clear();
+  static FMT_CONSTEXPR20 void grow(buffer<T>& buf, size_t) {
+    if (buf.size() != buffer_size) return;
+    static_cast<counting_buffer&>(buf).count_ += buf.size();
+    buf.clear();
   }
 
  public:
-  counting_buffer() : buffer<T>(data_, 0, buffer_size) {}
+  counting_buffer() : buffer<T>(grow, data_, 0, buffer_size) {}
 
   auto count() -> size_t { return count_ + this->size(); }
 };

include/fmt/format.h

@@ -880,27 +880,29 @@ class basic_memory_buffer final : public detail::buffer<T> {
   }
 
  protected:
-  FMT_CONSTEXPR20 void grow(size_t size) override {
+  static FMT_CONSTEXPR20 void grow(detail::buffer<T>& buf, size_t size) {
     detail::abort_fuzzing_if(size > 5000);
-    const size_t max_size = std::allocator_traits<Allocator>::max_size(alloc_);
-    size_t old_capacity = this->capacity();
+    auto& self = static_cast<basic_memory_buffer&>(buf);
+    const size_t max_size =
+        std::allocator_traits<Allocator>::max_size(self.alloc_);
+    size_t old_capacity = buf.capacity();
     size_t new_capacity = old_capacity + old_capacity / 2;
     if (size > new_capacity)
       new_capacity = size;
     else if (new_capacity > max_size)
       new_capacity = size > max_size ? size : max_size;
-    T* old_data = this->data();
+    T* old_data = buf.data();
     T* new_data =
-        std::allocator_traits<Allocator>::allocate(alloc_, new_capacity);
+        std::allocator_traits<Allocator>::allocate(self.alloc_, new_capacity);
     // Suppress a bogus -Wstringop-overflow in gcc 13.1 (#3481).
-    detail::assume(this->size() <= new_capacity);
+    detail::assume(buf.size() <= new_capacity);
     // The following code doesn't throw, so the raw pointer above doesn't leak.
-    std::uninitialized_copy_n(old_data, this->size(), new_data);
-    this->set(new_data, new_capacity);
+    std::uninitialized_copy_n(old_data, buf.size(), new_data);
+    self.set(new_data, new_capacity);
     // deallocate must not throw according to the standard, but even if it does,
     // the buffer already uses the new storage and will deallocate it in
     // destructor.
-    if (old_data != store_) alloc_.deallocate(old_data, old_capacity);
+    if (old_data != self.store_) self.alloc_.deallocate(old_data, old_capacity);
   }
 
  public:
@@ -909,7 +911,7 @@ class basic_memory_buffer final : public detail::buffer<T> {
 
   FMT_CONSTEXPR20 explicit basic_memory_buffer(
       const Allocator& alloc = Allocator())
-      : alloc_(alloc) {
+      : detail::buffer<T>(grow), alloc_(alloc) {
     this->set(store_, SIZE);
     if (detail::is_constant_evaluated()) detail::fill_n(store_, SIZE, T());
   }
@@ -941,7 +943,8 @@ class basic_memory_buffer final : public detail::buffer<T> {
     of the other object to it.
     \endrst
    */
-  FMT_CONSTEXPR20 basic_memory_buffer(basic_memory_buffer&& other) noexcept {
+  FMT_CONSTEXPR20 basic_memory_buffer(basic_memory_buffer&& other) noexcept
+      : detail::buffer<T>(grow) {
     move(other);
   }
 

include/fmt/os.h

@@ -377,9 +377,10 @@ struct ostream_params {
 };
 
 class file_buffer final : public buffer<char> {
+ private:
   file file_;
 
-  FMT_API void grow(size_t) override;
+  FMT_API static void grow(buffer<char>& buf, size_t);
 
  public:
   FMT_API file_buffer(cstring_view path, const ostream_params& params);

src/os.cc

@@ -370,18 +370,17 @@ long getpagesize() {
 
 namespace detail {
 
-void file_buffer::grow(size_t) {
-  if (this->size() == this->capacity()) flush();
+void file_buffer::grow(buffer<char>& buf, size_t) {
+  if (buf.size() == buf.capacity()) static_cast<file_buffer&>(buf).flush();
 }
 
-file_buffer::file_buffer(cstring_view path,
-                         const detail::ostream_params& params)
-    : file_(path, params.oflag) {
+file_buffer::file_buffer(cstring_view path, const ostream_params& params)
+    : buffer<char>(grow), file_(path, params.oflag) {
   set(new char[params.buffer_size], params.buffer_size);
 }
 
 file_buffer::file_buffer(file_buffer&& other)
-    : detail::buffer<char>(other.data(), other.size(), other.capacity()),
+    : buffer<char>(grow, other.data(), other.size(), other.capacity()),
       file_(std::move(other.file_)) {
   other.clear();
   other.set(nullptr, 0);

test/core-test.cc

@@ -143,11 +143,12 @@ TEST(buffer_test, indestructible) {
 template <typename T> struct mock_buffer final : buffer<T> {
   MOCK_METHOD(size_t, do_grow, (size_t));
 
-  void grow(size_t capacity) override {
-    this->set(this->data(), do_grow(capacity));
+  static void grow(buffer<T>& buf, size_t capacity) {
+    auto& self = static_cast<mock_buffer&>(buf);
+    self.set(buf.data(), self.do_grow(capacity));
   }
 
-  mock_buffer(T* data = nullptr, size_t buf_capacity = 0) {
+  mock_buffer(T* data = nullptr, size_t buf_capacity = 0) : buffer<T>(grow) {
     this->set(data, buf_capacity);
     ON_CALL(*this, do_grow(_)).WillByDefault(Invoke([](size_t capacity) {
       return capacity;
@@ -443,8 +444,9 @@ struct check_custom {
       -> test_result {
     struct test_buffer final : fmt::detail::buffer<char> {
       char data[10];
-      test_buffer() : fmt::detail::buffer<char>(data, 0, 10) {}
-      void grow(size_t) override {}
+      test_buffer()
+          : fmt::detail::buffer<char>([](buffer<char>&, size_t) {}, data, 0,
+                                      10) {}
     } buffer;
     auto parse_ctx = fmt::format_parse_context("");
     auto ctx = fmt::format_context(fmt::detail::buffer_appender<char>(buffer),

test/ostream-test.cc

@@ -135,8 +135,8 @@ TEST(ostream_test, write_to_ostream_max_size) {
 
   struct test_buffer final : fmt::detail::buffer<char> {
     explicit test_buffer(size_t size)
-        : fmt::detail::buffer<char>(nullptr, size, size) {}
-    void grow(size_t) override {}
+        : fmt::detail::buffer<char>([](buffer<char>&, size_t) {}, nullptr, size,
+                                    size) {}
   } buffer(max_size);
 
   struct mock_streambuf : std::streambuf {
@@ -292,8 +292,7 @@ TEST(ostream_test, closed_ofstream) {
 
 struct unlocalized {};
 
-auto operator<<(std::ostream& os, unlocalized)
-    -> std::ostream& {
+auto operator<<(std::ostream& os, unlocalized) -> std::ostream& {
   return os << 12345;
 }