string_type.h

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#ifndef DD__STRING_TYPE
#define DD__STRING_TYPE

#include <stddef.h>
#include <sstream>
#include <string>
#include <system_error>

#include "sql/stateless_allocator.h"  // Stateless_allocator

namespace dd {
/**
  Functor class which allocates memory for String_type. Implementation
  uses my_malloc with key_memory_DD_String_type.
*/
struct String_type_alloc {
  void *operator()(size_t s) const;
};

typedef Stateless_allocator<char, String_type_alloc> String_type_allocator;

/**
  Template alias for char-based std::basic_string.
*/
template <class A>
using Char_string_template = std::basic_string<char, std::char_traits<char>, A>;

typedef Char_string_template<String_type_allocator> String_type;

/**
  Template alias for char-based std::basic_stringstream.
 */
template <class A>
using Char_stringstream_template =
    std::basic_stringstream<char, std::char_traits<char>, A>;

/**
  Instantiation of std::basic_stringstream with the same allocator as
  String_type. This is needed since a std::basic_stringstream::str()
  returns a basic_string allocated with its own allocator. Note that
  this also means that it is difficult to use a different PSI key for
  the stream memory as that would mean the return type of
  Stringstream_type::str() would be different and incompatible with
  String_type.

  To work around this would require the creation of a temporary
  String_type from the string returned from stringstream::str().
*/
typedef Char_stringstream_template<String_type_allocator> Stringstream_type;

template <typename LEX_STRING_TYPE>
String_type make_string_type(const LEX_STRING_TYPE &lst) {
  return {lst.str, lst.length};
}
}  // namespace dd

namespace std {

/**
  Specialize std::hash for dd::String_type so that it can be
  used with unordered_ containers. Uses our standard murmur3_32
  implementation, and the same suitability restrictions apply.
  @see murmur3_32
*/
template <>
struct hash<dd::String_type> {
  typedef dd::String_type argument_type;
  typedef size_t result_type;

  size_t operator()(const dd::String_type &s) const;
};
}  // namespace std
#endif /* DD__STRING_TYPE */