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_H
17#define LLVM_ADT_OPTIONAL_H
18
19#include "llvm/ADT/None.h"
20#include "llvm/Support/AlignOf.h"
21#include "llvm/Support/Compiler.h"
22#include <cassert>
23#include <utility>
24
25namespace llvm {
26
27template<typename T>
28class Optional {
29  AlignedCharArrayUnion<T> storage;
30  bool hasVal;
31public:
32  Optional(NoneType) : hasVal(false) {}
33  explicit Optional() : hasVal(false) {}
34  Optional(const T &y) : hasVal(true) {
35    new (storage.buffer) T(y);
36  }
37  Optional(const Optional &O) : hasVal(O.hasVal) {
38    if (hasVal)
39      new (storage.buffer) T(*O);
40  }
41
42  Optional(T &&y) : hasVal(true) {
43    new (storage.buffer) T(std::forward<T>(y));
44  }
45  Optional(Optional<T> &&O) : hasVal(O) {
46    if (O) {
47      new (storage.buffer) T(std::move(*O));
48      O.reset();
49    }
50  }
51  Optional &operator=(T &&y) {
52    if (hasVal)
53      **this = std::move(y);
54    else {
55      new (storage.buffer) T(std::move(y));
56      hasVal = true;
57    }
58    return *this;
59  }
60  Optional &operator=(Optional &&O) {
61    if (!O)
62      reset();
63    else {
64      *this = std::move(*O);
65      O.reset();
66    }
67    return *this;
68  }
69
70  static inline Optional create(const T* y) {
71    return y ? Optional(*y) : Optional();
72  }
73
74  // FIXME: these assignments (& the equivalent const T&/const Optional& ctors)
75  // could be made more efficient by passing by value, possibly unifying them
76  // with the rvalue versions above - but this could place a different set of
77  // requirements (notably: the existence of a default ctor) when implemented
78  // in that way. Careful SFINAE to avoid such pitfalls would be required.
79  Optional &operator=(const T &y) {
80    if (hasVal)
81      **this = y;
82    else {
83      new (storage.buffer) T(y);
84      hasVal = true;
85    }
86    return *this;
87  }
88
89  Optional &operator=(const Optional &O) {
90    if (!O)
91      reset();
92    else
93      *this = *O;
94    return *this;
95  }
96
97  void reset() {
98    if (hasVal) {
99      (**this).~T();
100      hasVal = false;
101    }
102  }
103
104  ~Optional() {
105    reset();
106  }
107
108  const T* getPointer() const { assert(hasVal); return reinterpret_cast<const T*>(storage.buffer); }
109  T* getPointer() { assert(hasVal); return reinterpret_cast<T*>(storage.buffer); }
110  const T& getValue() const LLVM_LVALUE_FUNCTION { assert(hasVal); return *getPointer(); }
111  T& getValue() LLVM_LVALUE_FUNCTION { assert(hasVal); return *getPointer(); }
112
113  LLVM_EXPLICIT operator bool() const { return hasVal; }
114  bool hasValue() const { return hasVal; }
115  const T* operator->() const { return getPointer(); }
116  T* operator->() { return getPointer(); }
117  const T& operator*() const LLVM_LVALUE_FUNCTION { assert(hasVal); return *getPointer(); }
118  T& operator*() LLVM_LVALUE_FUNCTION { assert(hasVal); return *getPointer(); }
119
120#if LLVM_HAS_RVALUE_REFERENCE_THIS
121  T&& getValue() && { assert(hasVal); return std::move(*getPointer()); }
122  T&& operator*() && { assert(hasVal); return std::move(*getPointer()); }
123#endif
124};
125
126template <typename T> struct isPodLike;
127template <typename T> struct isPodLike<Optional<T> > {
128  // An Optional<T> is pod-like if T is.
129  static const bool value = isPodLike<T>::value;
130};
131
132/// \brief Poison comparison between two \c Optional objects. Clients needs to
133/// explicitly compare the underlying values and account for empty \c Optional
134/// objects.
135///
136/// This routine will never be defined. It returns \c void to help diagnose
137/// errors at compile time.
138template<typename T, typename U>
139void operator==(const Optional<T> &X, const Optional<U> &Y);
140
141/// \brief Poison comparison between two \c Optional objects. Clients needs to
142/// explicitly compare the underlying values and account for empty \c Optional
143/// objects.
144///
145/// This routine will never be defined. It returns \c void to help diagnose
146/// errors at compile time.
147template<typename T, typename U>
148void operator!=(const Optional<T> &X, const Optional<U> &Y);
149
150/// \brief Poison comparison between two \c Optional objects. Clients needs to
151/// explicitly compare the underlying values and account for empty \c Optional
152/// objects.
153///
154/// This routine will never be defined. It returns \c void to help diagnose
155/// errors at compile time.
156template<typename T, typename U>
157void operator<(const Optional<T> &X, const Optional<U> &Y);
158
159/// \brief Poison comparison between two \c Optional objects. Clients needs to
160/// explicitly compare the underlying values and account for empty \c Optional
161/// objects.
162///
163/// This routine will never be defined. It returns \c void to help diagnose
164/// errors at compile time.
165template<typename T, typename U>
166void operator<=(const Optional<T> &X, const Optional<U> &Y);
167
168/// \brief Poison comparison between two \c Optional objects. Clients needs to
169/// explicitly compare the underlying values and account for empty \c Optional
170/// objects.
171///
172/// This routine will never be defined. It returns \c void to help diagnose
173/// errors at compile time.
174template<typename T, typename U>
175void operator>=(const Optional<T> &X, const Optional<U> &Y);
176
177/// \brief Poison comparison between two \c Optional objects. Clients needs to
178/// explicitly compare the underlying values and account for empty \c Optional
179/// objects.
180///
181/// This routine will never be defined. It returns \c void to help diagnose
182/// errors at compile time.
183template<typename T, typename U>
184void operator>(const Optional<T> &X, const Optional<U> &Y);
185
186} // end llvm namespace
187
188#endif
189