Casting.h revision f5091b476c46333ecfcf095cd2e422e9748e9546 
1//===-- llvm/Support/Casting.h - Allow flexible, checked, casts -*- 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 defines the isa<X>(), cast<X>(), dyn_cast<X>(), cast_or_null<X>(),
11// and dyn_cast_or_null<X>() templates.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_SUPPORT_CASTING_H
16#define LLVM_SUPPORT_CASTING_H
17
18#include <cassert>
19
20namespace llvm {
21
22//===----------------------------------------------------------------------===//
23//                          isa<x> Support Templates
24//===----------------------------------------------------------------------===//
25
26// Define a template that can be specialized by smart pointers to reflect the
27// fact that they are automatically dereferenced, and are not involved with the
28// template selection process...  the default implementation is a noop.
29//
30template<typename From> struct simplify_type {
31  typedef       From SimpleType;        // The real type this represents...
32
33  // An accessor to get the real value...
34  static SimpleType &getSimplifiedValue(From &Val) { return Val; }
35};
36
37template<typename From> struct simplify_type<const From> {
38  typedef const From SimpleType;
39  static SimpleType &getSimplifiedValue(const From &Val) {
40    return simplify_type<From>::getSimplifiedValue(static_cast<From&>(Val));
41  }
42};
43
44// The core of the implementation of isa<X> is here; To and From should be
45// the names of classes.  This template can be specialized to customize the
46// implementation of isa<> without rewriting it from scratch.
47template <typename To, typename From>
48struct isa_impl {
49  static inline bool doit(const From &Val) {
50    return To::classof(&Val);
51  }
52};
53
54template <typename To, typename From> struct isa_impl_cl {
55  static inline bool doit(const From &Val) {
56    return isa_impl<To, From>::doit(Val);
57  }
58};
59
60template <typename To, typename From> struct isa_impl_cl<To, const From> {
61  static inline bool doit(const From &Val) {
62    return isa_impl<To, From>::doit(Val);
63  }
64};
65
66template <typename To, typename From> struct isa_impl_cl<To, From*> {
67  static inline bool doit(const From *Val) {
68    assert(Val && "isa<> used on a null pointer");
69    return isa_impl<To, From>::doit(*Val);
70  }
71};
72
73template <typename To, typename From> struct isa_impl_cl<To, const From*> {
74  static inline bool doit(const From *Val) {
75    assert(Val && "isa<> used on a null pointer");
76    return isa_impl<To, From>::doit(*Val);
77  }
78};
79
80template <typename To, typename From> struct isa_impl_cl<To, const From*const> {
81  static inline bool doit(const From *Val) {
82    assert(Val && "isa<> used on a null pointer");
83    return isa_impl<To, From>::doit(*Val);
84  }
85};
86
87template<typename To, typename From, typename SimpleFrom>
88struct isa_impl_wrap {
89  // When From != SimplifiedType, we can simplify the type some more by using
90  // the simplify_type template.
91  static bool doit(const From &Val) {
92    return isa_impl_wrap<To, SimpleFrom,
93      typename simplify_type<SimpleFrom>::SimpleType>::doit(
94                          simplify_type<From>::getSimplifiedValue(Val));
95  }
96};
97
98template<typename To, typename FromTy>
99struct isa_impl_wrap<To, FromTy, FromTy> {
100  // When From == SimpleType, we are as simple as we are going to get.
101  static bool doit(const FromTy &Val) {
102    return isa_impl_cl<To,FromTy>::doit(Val);
103  }
104};
105
106// isa<X> - Return true if the parameter to the template is an instance of the
107// template type argument.  Used like this:
108//
109//  if (isa<Type>(myVal)) { ... }
110//
111template <class X, class Y>
112inline bool isa(const Y &Val) {
113  return isa_impl_wrap<X, Y, typename simplify_type<Y>::SimpleType>::doit(Val);
114}
115
116//===----------------------------------------------------------------------===//
117//                          cast<x> Support Templates
118//===----------------------------------------------------------------------===//
119
120template<class To, class From> struct cast_retty;
121
122
123// Calculate what type the 'cast' function should return, based on a requested
124// type of To and a source type of From.
125template<class To, class From> struct cast_retty_impl {
126  typedef To& ret_type;         // Normal case, return Ty&
127};
128template<class To, class From> struct cast_retty_impl<To, const From> {
129  typedef const To &ret_type;   // Normal case, return Ty&
130};
131
132template<class To, class From> struct cast_retty_impl<To, From*> {
133  typedef To* ret_type;         // Pointer arg case, return Ty*
134};
135
136template<class To, class From> struct cast_retty_impl<To, const From*> {
137  typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
138};
139
140template<class To, class From> struct cast_retty_impl<To, const From*const> {
141  typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
142};
143
144
145template<class To, class From, class SimpleFrom>
146struct cast_retty_wrap {
147  // When the simplified type and the from type are not the same, use the type
148  // simplifier to reduce the type, then reuse cast_retty_impl to get the
149  // resultant type.
150  typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type;
151};
152
153template<class To, class FromTy>
154struct cast_retty_wrap<To, FromTy, FromTy> {
155  // When the simplified type is equal to the from type, use it directly.
156  typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type;
157};
158
159template<class To, class From>
160struct cast_retty {
161  typedef typename cast_retty_wrap<To, From,
162                   typename simplify_type<From>::SimpleType>::ret_type ret_type;
163};
164
165// Ensure the non-simple values are converted using the simplify_type template
166// that may be specialized by smart pointers...
167//
168template<class To, class From, class SimpleFrom> struct cast_convert_val {
169  // This is not a simple type, use the template to simplify it...
170  static typename cast_retty<To, From>::ret_type doit(const From &Val) {
171    return cast_convert_val<To, SimpleFrom,
172      typename simplify_type<SimpleFrom>::SimpleType>::doit(
173                          simplify_type<From>::getSimplifiedValue(Val));
174  }
175};
176
177template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
178  // This _is_ a simple type, just cast it.
179  static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) {
180    typename cast_retty<To, FromTy>::ret_type Res2
181     = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val);
182    return Res2;
183  }
184};
185
186
187
188// cast<X> - Return the argument parameter cast to the specified type.  This
189// casting operator asserts that the type is correct, so it does not return null
190// on failure.  It does not allow a null argument (use cast_or_null for that).
191// It is typically used like this:
192//
193//  cast<Instruction>(myVal)->getParent()
194//
195template <class X, class Y>
196inline typename cast_retty<X, Y>::ret_type cast(const Y &Val) {
197  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
198  return cast_convert_val<X, Y,
199                          typename simplify_type<Y>::SimpleType>::doit(Val);
200}
201
202// cast_or_null<X> - Functionally identical to cast, except that a null value is
203// accepted.
204//
205template <class X, class Y>
206inline typename cast_retty<X, Y*>::ret_type cast_or_null(Y *Val) {
207  if (Val == 0) return 0;
208  assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
209  return cast<X>(Val);
210}
211
212
213// dyn_cast<X> - Return the argument parameter cast to the specified type.  This
214// casting operator returns null if the argument is of the wrong type, so it can
215// be used to test for a type as well as cast if successful.  This should be
216// used in the context of an if statement like this:
217//
218//  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
219//
220
221template <class X, class Y>
222inline typename cast_retty<X, Y>::ret_type dyn_cast(const Y &Val) {
223  return isa<X>(Val) ? cast<X, Y>(Val) : 0;
224}
225
226// dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null
227// value is accepted.
228//
229template <class X, class Y>
230inline typename cast_retty<X, Y*>::ret_type dyn_cast_or_null(Y *Val) {
231  return (Val && isa<X>(Val)) ? cast<X>(Val) : 0;
232}
233
234} // End llvm namespace
235
236#endif
237