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      1 //===-- Optional.h - Simple variant for passing optional values ---*- C++ -*-=//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 //  This file provides Optional, a template class modeled in the spirit of
     11 //  OCaml's 'opt' variant.  The idea is to strongly type whether or not
     12 //  a value can be optional.
     13 //
     14 //===----------------------------------------------------------------------===//
     15 
     16 #ifndef LLVM_ADT_OPTIONAL
     17 #define LLVM_ADT_OPTIONAL
     18 
     19 #include <cassert>
     20 
     21 namespace llvm {
     22 
     23 template<typename T>
     24 class Optional {
     25   T x;
     26   unsigned hasVal : 1;
     27 public:
     28   explicit Optional() : x(), hasVal(false) {}
     29   Optional(const T &y) : x(y), hasVal(true) {}
     30 
     31   static inline Optional create(const T* y) {
     32     return y ? Optional(*y) : Optional();
     33   }
     34 
     35   Optional &operator=(const T &y) {
     36     x = y;
     37     hasVal = true;
     38     return *this;
     39   }
     40 
     41   const T* getPointer() const { assert(hasVal); return &x; }
     42   const T& getValue() const { assert(hasVal); return x; }
     43 
     44   operator bool() const { return hasVal; }
     45   bool hasValue() const { return hasVal; }
     46   const T* operator->() const { return getPointer(); }
     47   const T& operator*() const { assert(hasVal); return x; }
     48 };
     49 
     50 template<typename T> struct simplify_type;
     51 
     52 template <typename T>
     53 struct simplify_type<const Optional<T> > {
     54   typedef const T* SimpleType;
     55   static SimpleType getSimplifiedValue(const Optional<T> &Val) {
     56     return Val.getPointer();
     57   }
     58 };
     59 
     60 template <typename T>
     61 struct simplify_type<Optional<T> >
     62   : public simplify_type<const Optional<T> > {};
     63 
     64 /// \brief Poison comparison between two \c Optional objects. Clients needs to
     65 /// explicitly compare the underlying values and account for empty \c Optional
     66 /// objects.
     67 ///
     68 /// This routine will never be defined. It returns \c void to help diagnose
     69 /// errors at compile time.
     70 template<typename T, typename U>
     71 void operator==(const Optional<T> &X, const Optional<U> &Y);
     72 
     73 /// \brief Poison comparison between two \c Optional objects. Clients needs to
     74 /// explicitly compare the underlying values and account for empty \c Optional
     75 /// objects.
     76 ///
     77 /// This routine will never be defined. It returns \c void to help diagnose
     78 /// errors at compile time.
     79 template<typename T, typename U>
     80 void operator!=(const Optional<T> &X, const Optional<U> &Y);
     81 
     82 /// \brief Poison comparison between two \c Optional objects. Clients needs to
     83 /// explicitly compare the underlying values and account for empty \c Optional
     84 /// objects.
     85 ///
     86 /// This routine will never be defined. It returns \c void to help diagnose
     87 /// errors at compile time.
     88 template<typename T, typename U>
     89 void operator<(const Optional<T> &X, const Optional<U> &Y);
     90 
     91 /// \brief Poison comparison between two \c Optional objects. Clients needs to
     92 /// explicitly compare the underlying values and account for empty \c Optional
     93 /// objects.
     94 ///
     95 /// This routine will never be defined. It returns \c void to help diagnose
     96 /// errors at compile time.
     97 template<typename T, typename U>
     98 void operator<=(const Optional<T> &X, const Optional<U> &Y);
     99 
    100 /// \brief Poison comparison between two \c Optional objects. Clients needs to
    101 /// explicitly compare the underlying values and account for empty \c Optional
    102 /// objects.
    103 ///
    104 /// This routine will never be defined. It returns \c void to help diagnose
    105 /// errors at compile time.
    106 template<typename T, typename U>
    107 void operator>=(const Optional<T> &X, const Optional<U> &Y);
    108 
    109 /// \brief Poison comparison between two \c Optional objects. Clients needs to
    110 /// explicitly compare the underlying values and account for empty \c Optional
    111 /// objects.
    112 ///
    113 /// This routine will never be defined. It returns \c void to help diagnose
    114 /// errors at compile time.
    115 template<typename T, typename U>
    116 void operator>(const Optional<T> &X, const Optional<U> &Y);
    117 
    118 } // end llvm namespace
    119 
    120 #endif
    121