knotkit/lib/maybe.h
2011-12-09 15:50:25 -05:00

59 lines
1.1 KiB
C++

template <class T>
class maybe
{
private:
bool present;
T v;
public:
maybe () : present(0) { }
maybe (const T &v_) : present(1), v(v_) { }
maybe (const maybe &m) : present(m.present), v(m.v) { }
maybe (reader &r);
~maybe () { }
maybe &operator = (const maybe &m) { present = m.present; v = m.v; return *this; }
bool is_some () const { return present; }
bool is_none () const { return !present; }
T &some () { assert (present); return v; }
bool operator == (const maybe &m) const
{
if (present != m.present)
return 0;
if (present)
return v == m.v;
}
bool operator != (const maybe &m) const { return !operator == (m); }
void write_self (writer &w) const;
hash_t hash_self () const;
};
template<class T>
maybe<T>::maybe (reader &r)
{
read (r, present);
if (present)
read (r, v);
}
template<class T> void
maybe<T>::write_self (writer &w) const
{
write (w, present);
if (present)
write (w, v);
}
template<class T> hash_t
maybe<T>::hash_self () const
{
if (present)
return hash_combine (hash (0xdeadbeef), hash (v));
else
return hash (0xcafebabe);
}