1 //===- Any.h - Generic type erased holder of any type -----------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 //  This file provides Any, a non-template class modeled in the spirit of
10 //  std::any.  The idea is to provide a type-safe replacement for C's void*.
11 //  It can hold a value of any copy-constructible copy-assignable type
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_ADT_ANY_H
16 #define LLVM_ADT_ANY_H
17 
18 #include "llvm/ADT/STLExtras.h"
19 
20 #include <cassert>
21 #include <memory>
22 #include <type_traits>
23 
24 namespace llvm {
25 
26 class LLVM_EXTERNAL_VISIBILITY Any {
27 
28   // The `Typeid<T>::Id` static data member below is a globally unique
29   // identifier for the type `T`. It is explicitly marked with default
30   // visibility so that when `-fvisibility=hidden` is used, the loader still
31   // merges duplicate definitions across DSO boundaries.
32   template <typename T> struct TypeId { static const char Id; };
33 
34   struct StorageBase {
35     virtual ~StorageBase() = default;
36     virtual std::unique_ptr<StorageBase> clone() const = 0;
37     virtual const void *id() const = 0;
38   };
39 
40   template <typename T> struct StorageImpl : public StorageBase {
41     explicit StorageImpl(const T &Value) : Value(Value) {}
42 
43     explicit StorageImpl(T &&Value) : Value(std::move(Value)) {}
44 
45     std::unique_ptr<StorageBase> clone() const override {
46       return std::make_unique<StorageImpl<T>>(Value);
47     }
48 
49     const void *id() const override { return &TypeId<T>::Id; }
50 
51     T Value;
52 
53   private:
54     StorageImpl &operator=(const StorageImpl &Other) = delete;
55     StorageImpl(const StorageImpl &Other) = delete;
56   };
57 
58 public:
59   Any() = default;
60 
61   Any(const Any &Other)
62       : Storage(Other.Storage ? Other.Storage->clone() : nullptr) {}
63 
64   // When T is Any or T is not copy-constructible we need to explicitly disable
65   // the forwarding constructor so that the copy constructor gets selected
66   // instead.
67   template <typename T,
68             std::enable_if_t<
69                 llvm::conjunction<
70                     llvm::negation<std::is_same<std::decay_t<T>, Any>>,
71                     // We also disable this overload when an `Any` object can be
72                     // converted to the parameter type because in that case,
73                     // this constructor may combine with that conversion during
74                     // overload resolution for determining copy
75                     // constructibility, and then when we try to determine copy
76                     // constructibility below we may infinitely recurse. This is
77                     // being evaluated by the standards committee as a potential
78                     // DR in `std::any` as well, but we're going ahead and
79                     // adopting it to work-around usage of `Any` with types that
80                     // need to be implicitly convertible from an `Any`.
81                     llvm::negation<std::is_convertible<Any, std::decay_t<T>>>,
82                     std::is_copy_constructible<std::decay_t<T>>>::value,
83                 int> = 0>
84   Any(T &&Value) {
85     Storage =
86         std::make_unique<StorageImpl<std::decay_t<T>>>(std::forward<T>(Value));
87   }
88 
89   Any(Any &&Other) : Storage(std::move(Other.Storage)) {}
90 
91   Any &swap(Any &Other) {
92     std::swap(Storage, Other.Storage);
93     return *this;
94   }
95 
96   Any &operator=(Any Other) {
97     Storage = std::move(Other.Storage);
98     return *this;
99   }
100 
101   bool hasValue() const { return !!Storage; }
102 
103   void reset() { Storage.reset(); }
104 
105 private:
106   template <class T> friend T any_cast(const Any &Value);
107   template <class T> friend T any_cast(Any &Value);
108   template <class T> friend T any_cast(Any &&Value);
109   template <class T> friend const T *any_cast(const Any *Value);
110   template <class T> friend T *any_cast(Any *Value);
111   template <typename T> friend bool any_isa(const Any &Value);
112 
113   std::unique_ptr<StorageBase> Storage;
114 };
115 
116 template <typename T> const char Any::TypeId<T>::Id = 0;
117 
118 
119 template <typename T> bool any_isa(const Any &Value) {
120   if (!Value.Storage)
121     return false;
122   return Value.Storage->id() == &Any::TypeId<remove_cvref_t<T>>::Id;
123 }
124 
125 template <class T> T any_cast(const Any &Value) {
126   return static_cast<T>(*any_cast<remove_cvref_t<T>>(&Value));
127 }
128 
129 template <class T> T any_cast(Any &Value) {
130   return static_cast<T>(*any_cast<remove_cvref_t<T>>(&Value));
131 }
132 
133 template <class T> T any_cast(Any &&Value) {
134   return static_cast<T>(std::move(*any_cast<remove_cvref_t<T>>(&Value)));
135 }
136 
137 template <class T> const T *any_cast(const Any *Value) {
138   using U = remove_cvref_t<T>;
139   assert(Value && any_isa<T>(*Value) && "Bad any cast!");
140   if (!Value || !any_isa<U>(*Value))
141     return nullptr;
142   return &static_cast<Any::StorageImpl<U> &>(*Value->Storage).Value;
143 }
144 
145 template <class T> T *any_cast(Any *Value) {
146   using U = std::decay_t<T>;
147   assert(Value && any_isa<U>(*Value) && "Bad any cast!");
148   if (!Value || !any_isa<U>(*Value))
149     return nullptr;
150   return &static_cast<Any::StorageImpl<U> &>(*Value->Storage).Value;
151 }
152 
153 } // end namespace llvm
154 
155 #endif // LLVM_ADT_ANY_H
156