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/********************* */
/*! \file maybe.h
** \verbatim
** Top contributors (to current version):
** Tim King
** This file is part of the CVC4 project.
** Copyright (c) 2009-2019 by the authors listed in the file AUTHORS
** in the top-level source directory) and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief This provides a templated Maybe construct.
**
** This class provides a templated Maybe<T> construct.
** This follows the rough pattern of the Maybe monad in haskell.
** A Maybe is an algebraic type that is either Nothing | Just T
**
** T must support T() and operator=.
**
** This has a couple of uses:
** - There is no reasonable value or particularly clean way to represent
** Nothing using a value of T
** - High level of assurance that a value is not used before it is set.
**/
#include "cvc4_public.h"
#ifndef __CVC4__UTIL__MAYBE_H
#define __CVC4__UTIL__MAYBE_H
#include <ostream>
#include "base/exception.h"
namespace CVC4 {
template <class T>
class CVC4_PUBLIC Maybe
{
public:
Maybe() : d_just(false), d_value(){}
Maybe(const T& val): d_just(true), d_value(val){}
Maybe& operator=(const T& v){
d_just = true;
d_value = v;
return *this;
}
inline bool nothing() const { return !d_just; }
inline bool just() const { return d_just; }
explicit operator bool() const noexcept { return just(); }
void clear() {
if(just()){
d_just = false;
d_value = T();
}
}
const T& value() const
{
if (nothing())
{
throw Exception("Maybe::value() requires the maybe to be set.");
}
return d_value;
}
private:
bool d_just;
T d_value;
};
template <class T>
inline std::ostream& operator<<(std::ostream& out, const Maybe<T>& m){
out << "{";
if(m.nothing()){
out << "Nothing";
}else{
out << "Just ";
out << m.value();
}
out << "}";
return out;
}
}/* CVC4 namespace */
#endif /* __CVC4__UTIL__MAYBE_H */
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