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// **************************************************************************
// * This file is part of the FreeFileSync project. It is distributed under *
// * GNU General Public License: http://www.gnu.org/licenses/gpl.html *
// * Copyright (C) Zenju (zenju AT gmx DOT de) - All Rights Reserved *
// **************************************************************************
#ifndef OPTIONAL_H_2857428578342203589
#define OPTIONAL_H_2857428578342203589
namespace zen
{
/*
Optional return value without heap memory allocation!
-> interface like a pointer, performance like a value
Usage:
------
Opt<MyEnum> someFunction();
{
if (allIsWell)
return enumVal;
else
return NoValue();
}
Opt<MyEnum> optValue = someFunction();
if (optValue)
... use *optValue ...
*/
struct NoValue {};
template <class T>
class Opt
{
public:
Opt() : value() , valid(false) {}
Opt(NoValue) : value() , valid(false) {}
Opt(const T& val) : value(val), valid(true ) {}
Opt(const Opt& tmp) : value(tmp.valid ? tmp.value : T()), valid(tmp.valid) {}
Opt& operator=(const Opt& tmp)
{
if (tmp.valid)
value = tmp.value;
valid = tmp.valid;
}
////rvalue optimization: only basic exception safety:
// Opt(Opt&& tmp) : value(std::move(tmp.value)), valid(tmp.valid) {}
#ifdef _MSC_VER
private:
struct ConversionToBool { int dummy; };
public:
operator int ConversionToBool::* () const { return valid ? &ConversionToBool::dummy : nullptr; }
#else
explicit operator bool() const { return valid; } //thank you C++11!!!
#endif
const T& operator*() const { return value; }
/**/ T& operator*() { return value; }
const T* operator->() const { return &value; }
/**/ T* operator->() { return &value; }
void reset() { valid = false; }
private:
T value;
bool valid;
};
}
#endif //OPTIONAL_H_2857428578342203589
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