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#ifndef __NR_MAYBE_H__
#define __NR_MAYBE_H__
/*
* Nullable values for C++
*
* Copyright 2004, 2007 MenTaLguY <mental@rydia.net>
*
* This code is licensed under the GNU GPL; see COPYING for more information.
*/
#if HAVE_CONFIG_H
#include "config.h"
#endif
#include <stdexcept>
#include <string>
#include <algorithm>
namespace NR {
class IsNothing : public std::domain_error {
public:
IsNothing() : domain_error(std::string("Is nothing")) {}
};
struct Nothing {};
template <typename T>
class MaybeStorage {
public:
MaybeStorage() : _is_nothing(true) {}
MaybeStorage(T const &value)
: _value(value), _is_nothing(false) {}
bool is_nothing() const { return _is_nothing; }
T &value() { return _value; }
T const &value() const { return _value; }
private:
T _value;
bool _is_nothing;
};
template <typename T>
class Maybe {
public:
Maybe() {}
Maybe(Nothing) {}
Maybe(T const &t) : _storage(t) {}
Maybe(Maybe const &m) : _storage(m._storage) {}
template <typename T2>
Maybe(Maybe<T2> const &m) {
if (m) {
_storage = *m;
}
}
template <typename T2>
Maybe(Maybe<T2 const &> m) {
if (m) {
_storage = *m;
}
}
operator bool() const { return !_storage.is_nothing(); }
T const &operator*() const throw(IsNothing) {
if (_storage.is_nothing()) {
throw IsNothing();
} else {
return _storage.value();
}
}
T &operator*() throw(IsNothing) {
if (_storage.is_nothing()) {
throw IsNothing();
} else {
return _storage.value();
}
}
T const *operator->() const throw(IsNothing) {
if (_storage.is_nothing()) {
throw IsNothing();
} else {
return &_storage.value();
}
}
T *operator->() throw(IsNothing) {
if (_storage.is_nothing()) {
throw IsNothing();
} else {
return &_storage.value();
}
}
template <typename T2>
bool operator==(Maybe<T2> const &other) const {
bool is_nothing = _storage.is_nothing();
if ( is_nothing || !other ) {
return is_nothing && !other;
} else {
return _storage.value() == *other;
}
}
template <typename T2>
bool operator!=(Maybe<T2> const &other) const {
bool is_nothing = _storage.is_nothing();
if ( is_nothing || !other ) {
return !is_nothing || other;
} else {
return _storage.value() != *other;
}
}
private:
MaybeStorage<T> _storage;
};
template <typename T>
class Maybe<T &> {
public:
Maybe() : _ref(NULL) {}
Maybe(Nothing) : _ref(NULL) {}
Maybe(T &t) : _ref(&t) {}
template <typename T2>
Maybe(Maybe<T2> const &m) {
if (m) {
_ref = &*m;
}
}
template <typename T2>
Maybe(Maybe<T2 &> m) {
if (m) {
_ref = *m;
}
}
template <typename T2>
Maybe(Maybe<T2 const &> m) {
if (m) {
_ref = *m;
}
}
operator bool() const { return _ref; }
T &operator*() const throw(IsNothing) {
if (!_ref) {
throw IsNothing();
} else {
return *_ref;
}
}
T *operator->() const throw(IsNothing) {
if (!_ref) {
throw IsNothing();
} else {
return _ref;
}
}
template <typename T2>
bool operator==(Maybe<T2> const &other) const {
if ( !_ref || !other ) {
return !_ref && !other;
} else {
return *_ref == *other;
}
}
template <typename T2>
bool operator!=(Maybe <T2> const &other) const {
if ( !_ref || !other ) {
return _ref || other;
} else {
return *_ref != *other;
}
}
private:
T *_ref;
};
} /* namespace NR */
#endif
/*
Local Variables:
mode:c++
c-file-style:"stroustrup"
c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
indent-tabs-mode:nil
fill-column:99
End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=99 :
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