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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-3.0 *
// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
// *****************************************************************************
#ifndef OPTIONAL_H_2857428578342203589
#define OPTIONAL_H_2857428578342203589
#include <cassert>
#include <type_traits>
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() {}
Opt(NoValue) {}
Opt(const T& val) : valid_(true) { new (&rawMem_) T(val); } //throw X
Opt( T&& tmp) : valid_(true) { new (&rawMem_) T(std::move(tmp)); }
Opt(const Opt& other) : valid_(other.valid_)
{
if (const T* val = other.get())
new (&rawMem_) T(*val); //throw X
}
~Opt() { if (T* val = get()) val->~T(); }
Opt& operator=(NoValue) //support assignment to Opt<const T>
{
if (T* val = get())
{
valid_ = false;
val->~T();
}
return *this;
}
Opt& operator=(const Opt& other) //strong exception-safety iff T::operator=() is strongly exception-safe
{
if (T* val = get())
{
if (const T* valOther = other.get())
*val = *valOther; //throw X
else
{
valid_ = false;
val->~T();
}
}
else if (const T* valOther = other.get())
{
new (&rawMem_) T(*valOther); //throw X
valid_ = true;
}
return *this;
}
explicit operator bool() const { return valid_; } //thank you, C++11!!!
const T* get() const { return valid_ ? reinterpret_cast<const T*>(&rawMem_) : nullptr; }
T* get() { return valid_ ? reinterpret_cast< T*>(&rawMem_) : nullptr; }
const T& operator*() const { return *get(); }
/**/ T& operator*() { return *get(); }
const T* operator->() const { return get(); }
/**/ T* operator->() { return get(); }
private:
std::aligned_storage_t<sizeof(T), alignof(T)> rawMem_; //don't require T to be default-constructible!
bool valid_ = false;
};
}
#endif //OPTIONAL_H_2857428578342203589
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