string_counter.h

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// Copyright (c) 2025, Oracle and/or its affiliates.
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License, version 2.0,
// as published by the Free Software Foundation.
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#ifndef MYSQL_STRCONV_ENCODE_STRING_COUNTER_H
#define MYSQL_STRCONV_ENCODE_STRING_COUNTER_H
 
/// @file
/// Experimental API header
 
#include <string_view>                           // string_view
#include "mysql/strconv/encode/string_target.h"  // String_target_interface
 
/// @addtogroup GroupLibsMysqlStrconv
/// @{
 
namespace mysql::strconv {
 
/// Class that serves as the target for encode(..., Is_string_target), which
/// never writes anything and only stores the size.
class String_counter : public detail::String_target_interface<String_counter> {
 protected:
  /// Construct a new object.
  ///
  /// This is hidden from user code. These object are only meant to be created
  /// internally by the framework.
  String_counter() = default;
 
 public:
  static constexpr Target_type target_type = Target_type::counter;
 
  // Allow move, but not copy.
  //
  // Deleting copy semantics protects against the mistake of making a
  // `encode_impl` function take its second parameter by value.
  String_counter(const String_counter &) = delete;
  String_counter(String_counter &&) noexcept = default;
  String_counter &operator=(const String_counter &) = delete;
  String_counter &operator=(String_counter &&) noexcept = default;
  ~String_counter() = default;
 
  /// Increment the size by `sv.size()`.
  void write_raw(const std::string_view &sv) { advance(sv.size()); }
 
  /// Increment the size by 1.
  void write_char(int) { advance(1); }
 
  /// Increment the size by the size of the given object.
  void write(const Is_format auto &format, const auto &object) {
    resolve_format_and_write(format, object);
  }
 
  /// Increment the size by the size of the given string. This overload enables
  /// writing string literals directly.
  void write(const Is_format auto &format, const std::string_view &sv) {
    resolve_format_and_write(format, sv);
  }
 
  /// Increment the size by `size`.
  void advance(std::size_t size) { m_size += size; }
 
  /// Return the current size.
  [[nodiscard]] std::size_t size() const { return m_size; }
 
 private:
  /// The current size.
  std::size_t m_size{0};
};  // class String_counter
 
}  // namespace mysql::strconv
 
namespace mysql::strconv::detail {
 
/// String_counter subclass that can be instantiated.
///
/// We hide this in the detail namespace because the class is not supposed to be
/// instantiated in user code, only in this framework.
class Constructible_string_counter : public String_counter {
 public:
  Constructible_string_counter() = default;
};
 
static_assert(!std::copy_constructible<Constructible_string_counter>);
static_assert(!std::copy_constructible<String_counter>);
static_assert(std::movable<Constructible_string_counter>);
static_assert(std::movable<String_counter>);
 
}  // namespace mysql::strconv::detail
 
// addtogroup GroupLibsMysqlStrconv
/// @}
 
#endif  // ifndef MYSQL_STRCONV_ENCODE_STRING_COUNTER_H