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/****************************************************************************** |
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* Top contributors (to current version): |
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* Tim King, Mathias Preiner |
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* |
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* This file is part of the cvc5 project. |
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* |
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* Copyright (c) 2009-2021 by the authors listed in the file AUTHORS |
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* in the top-level source directory and their institutional affiliations. |
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* All rights reserved. See the file COPYING in the top-level source |
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* directory for licensing information. |
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* **************************************************************************** |
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* |
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* This provides a templated Maybe construct. |
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* |
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* This class provides a templated Maybe<T> construct. |
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* This follows the rough pattern of the Maybe monad in haskell. |
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* A Maybe is an algebraic type that is either Nothing | Just T |
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* |
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* T must support T() and operator=. |
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* |
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* This has a couple of uses: |
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* - There is no reasonable value or particularly clean way to represent |
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* Nothing using a value of T |
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* - High level of assurance that a value is not used before it is set. |
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*/ |
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#include "cvc5_public.h" |
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#ifndef CVC5__UTIL__MAYBE_H |
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#define CVC5__UTIL__MAYBE_H |
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#include <ostream> |
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#include "base/exception.h" |
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namespace cvc5 { |
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template <class T> |
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class Maybe |
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{ |
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public: |
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Maybe() : d_just(false), d_value(){} |
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Maybe(const T& val): d_just(true), d_value(val){} |
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Maybe& operator=(const T& v){ |
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d_just = true; |
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d_value = v; |
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return *this; |
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} |
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inline bool nothing() const { return !d_just; } |
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inline bool just() const { return d_just; } |
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explicit operator bool() const noexcept { return just(); } |
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void clear() { |
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if(just()){ |
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d_just = false; |
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d_value = T(); |
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} |
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} |
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const T& value() const |
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{ |
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if (nothing()) |
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{ |
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throw Exception("Maybe::value() requires the maybe to be set."); |
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} |
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return d_value; |
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} |
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private: |
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bool d_just; |
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T d_value; |
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}; |
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template <class T> |
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inline std::ostream& operator<<(std::ostream& out, const Maybe<T>& m){ |
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out << "{"; |
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if(m.nothing()){ |
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out << "Nothing"; |
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}else{ |
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out << "Just "; |
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out << m.value(); |
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} |
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out << "}"; |
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return out; |
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} |
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} // namespace cvc5 |
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#endif /* CVC5__UTIL__MAYBE_H */ |