ClickHouse/libs/libmysqlxx/include/mysqlxx/Null.h
2018-06-04 18:28:25 +03:00

97 lines
2.1 KiB
C++

#pragma once
#include <mysqlxx/Exception.h>
namespace mysqlxx
{
struct NullType {};
const NullType null = {};
/** Store NULL-able types from MySQL.
* Usage example:
* mysqlxx::Null<int> x = mysqlxx::null;
* std::cout << (x.isNull() ? "Ok." : "Fail.") << std::endl;
* x = 10;
*/
template <typename T>
class Null
{
public:
T data {};
bool is_null = true;
Null() : is_null(true) {}
Null(const Null<T> &) = default;
Null(Null<T> &&) noexcept = default;
Null(NullType data) : is_null(true) {}
explicit Null(const T & data_) : data(data_), is_null(false) {}
operator T & ()
{
if (is_null)
throw Exception("Value is NULL");
return data;
}
operator const T & () const
{
if (is_null)
throw Exception("Value is NULL");
return data;
}
Null<T> & operator= (Null<T> &&) noexcept = default;
Null<T> & operator= (const Null<T> &) = default;
Null<T> & operator= (const T & data_) { is_null = false; data = data_; return *this; }
Null<T> & operator= (const NullType other) { is_null = true; data = T(); return *this; }
bool isNull() const { return is_null; }
bool operator< (const Null<T> & other) const
{
return is_null < other.is_null
|| (is_null == other.is_null && data < other.data);
}
bool operator< (const NullType other) const { return false; }
bool operator== (const Null<T> & other) const
{
return is_null == other.is_null && data == other.data;
}
bool operator== (const T & other) const
{
return !is_null && data == other;
}
bool operator== (const NullType other) const { return is_null; }
bool operator!= (const Null<T> & other) const
{
return !(*this == other);
}
bool operator!= (const NullType other) const { return !is_null; }
bool operator!= (const T & other) const
{
return is_null || data != other;
}
};
template<typename T>
T getValueFromNull(const Null<T> & maybe)
{
if (maybe.isNull())
return {};
return maybe;
}
}