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 Any {
27   template <typename T> struct TypeId { static const char Id; };
28 
29   struct StorageBase {
30     virtual ~StorageBase() = default;
31     virtual std::unique_ptr<StorageBase> clone() const = 0;
32     virtual const void *id() const = 0;
33   };
34 
35   template <typename T> struct StorageImpl : public StorageBase {
36     explicit StorageImpl(const T &Value) : Value(Value) {}
37 
38     explicit StorageImpl(T &&Value) : Value(std::move(Value)) {}
39 
40     std::unique_ptr<StorageBase> clone() const override {
41       return std::make_unique<StorageImpl<T>>(Value);
42     }
43 
44     const void *id() const override { return &TypeId<T>::Id; }
45 
46     T Value;
47 
48   private:
49     StorageImpl &operator=(const StorageImpl &Other) = delete;
50     StorageImpl(const StorageImpl &Other) = delete;
51   };
52 
53 public:
54   Any() = default;
55 
56   Any(const Any &Other)
57       : Storage(Other.Storage ? Other.Storage->clone() : nullptr) {}
58 
59   // When T is Any or T is not copy-constructible we need to explicitly disable
60   // the forwarding constructor so that the copy constructor gets selected
61   // instead.
62   template <
63       typename T,
64       typename std::enable_if<
65           llvm::conjunction<
66               llvm::negation<std::is_same<typename std::decay<T>::type, Any>>,
67               // We also disable this overload when an `Any` object can be
68               // converted to the parameter type because in that case, this
69               // constructor may combine with that conversion during overload
70               // resolution for determining copy constructibility, and then
71               // when we try to determine copy constructibility below we may
72               // infinitely recurse. This is being evaluated by the standards
73               // committee as a potential DR in `std::any` as well, but we're
74               // going ahead and adopting it to work-around usage of `Any` with
75               // types that need to be implicitly convertible from an `Any`.
76               llvm::negation<std::is_convertible<Any, typename std::decay<T>::type>>,
77               std::is_copy_constructible<typename std::decay<T>::type>>::value,
78           int>::type = 0>
79   Any(T &&Value) {
80     using U = typename std::decay<T>::type;
81     Storage = std::make_unique<StorageImpl<U>>(std::forward<T>(Value));
82   }
83 
84   Any(Any &&Other) : Storage(std::move(Other.Storage)) {}
85 
86   Any &swap(Any &Other) {
87     std::swap(Storage, Other.Storage);
88     return *this;
89   }
90 
91   Any &operator=(Any Other) {
92     Storage = std::move(Other.Storage);
93     return *this;
94   }
95 
96   bool hasValue() const { return !!Storage; }
97 
98   void reset() { Storage.reset(); }
99 
100 private:
101   template <class T> friend T any_cast(const Any &Value);
102   template <class T> friend T any_cast(Any &Value);
103   template <class T> friend T any_cast(Any &&Value);
104   template <class T> friend const T *any_cast(const Any *Value);
105   template <class T> friend T *any_cast(Any *Value);
106   template <typename T> friend bool any_isa(const Any &Value);
107 
108   std::unique_ptr<StorageBase> Storage;
109 };
110 
111 template <typename T> const char Any::TypeId<T>::Id = 0;
112 
113 
114 template <typename T> bool any_isa(const Any &Value) {
115   if (!Value.Storage)
116     return false;
117   using U =
118       typename std::remove_cv<typename std::remove_reference<T>::type>::type;
119   return Value.Storage->id() == &Any::TypeId<U>::Id;
120 }
121 
122 template <class T> T any_cast(const Any &Value) {
123   using U =
124       typename std::remove_cv<typename std::remove_reference<T>::type>::type;
125   return static_cast<T>(*any_cast<U>(&Value));
126 }
127 
128 template <class T> T any_cast(Any &Value) {
129   using U =
130       typename std::remove_cv<typename std::remove_reference<T>::type>::type;
131   return static_cast<T>(*any_cast<U>(&Value));
132 }
133 
134 template <class T> T any_cast(Any &&Value) {
135   using U =
136       typename std::remove_cv<typename std::remove_reference<T>::type>::type;
137   return static_cast<T>(std::move(*any_cast<U>(&Value)));
138 }
139 
140 template <class T> const T *any_cast(const Any *Value) {
141   using U =
142       typename std::remove_cv<typename std::remove_reference<T>::type>::type;
143   assert(Value && any_isa<T>(*Value) && "Bad any cast!");
144   if (!Value || !any_isa<U>(*Value))
145     return nullptr;
146   return &static_cast<Any::StorageImpl<U> &>(*Value->Storage).Value;
147 }
148 
149 template <class T> T *any_cast(Any *Value) {
150   using U = typename std::decay<T>::type;
151   assert(Value && any_isa<U>(*Value) && "Bad any cast!");
152   if (!Value || !any_isa<U>(*Value))
153     return nullptr;
154   return &static_cast<Any::StorageImpl<U> &>(*Value->Storage).Value;
155 }
156 
157 } // end namespace llvm
158 
159 #endif // LLVM_ADT_ANY_H
160