Casting.h revision 7fe65d691dcce550d53ec9310913aab67ab6d654 
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 "llvm/Support/type_traits.h"
19#include <cassert>
20
21namespace llvm {
22
23//===----------------------------------------------------------------------===//
24//                          isa<x> Support Templates
25//===----------------------------------------------------------------------===//
26
27// Define a template that can be specialized by smart pointers to reflect the
28// fact that they are automatically dereferenced, and are not involved with the
29// template selection process...  the default implementation is a noop.
30//
31template<typename From> struct simplify_type {
32  typedef       From SimpleType;        // The real type this represents...
33
34  // An accessor to get the real value...
35  static SimpleType &getSimplifiedValue(From &Val) { return Val; }
36};
37
38template<typename From> struct simplify_type<const From> {
39  typedef typename simplify_type<From>::SimpleType NonConstSimpleType;
40  typedef typename add_const_past_pointer<NonConstSimpleType>::type
41    SimpleType;
42  typedef typename add_lvalue_reference_if_not_pointer<SimpleType>::type
43    RetType;
44  static RetType getSimplifiedValue(const From& Val) {
45    return simplify_type<From>::getSimplifiedValue(const_cast<From&>(Val));
46  }
47};
48
49// The core of the implementation of isa<X> is here; To and From should be
50// the names of classes.  This template can be specialized to customize the
51// implementation of isa<> without rewriting it from scratch.
52template <typename To, typename From, typename Enabler = void>
53struct isa_impl {
54  static inline bool doit(const From &Val) {
55    return To::classof(&Val);
56  }
57};
58
59/// \brief Always allow upcasts, and perform no dynamic check for them.
60template <typename To, typename From>
61struct isa_impl<To, From,
62                typename enable_if<
63                  llvm::is_base_of<To, From>
64                >::type
65               > {
66  static inline bool doit(const From &) { return true; }
67};
68
69template <typename To, typename From> struct isa_impl_cl {
70  static inline bool doit(const From &Val) {
71    return isa_impl<To, From>::doit(Val);
72  }
73};
74
75template <typename To, typename From> struct isa_impl_cl<To, const From> {
76  static inline bool doit(const From &Val) {
77    return isa_impl<To, From>::doit(Val);
78  }
79};
80
81template <typename To, typename From> struct isa_impl_cl<To, From*> {
82  static inline bool doit(const From *Val) {
83    assert(Val && "isa<> used on a null pointer");
84    return isa_impl<To, From>::doit(*Val);
85  }
86};
87
88template <typename To, typename From> struct isa_impl_cl<To, From*const> {
89  static inline bool doit(const From *Val) {
90    assert(Val && "isa<> used on a null pointer");
91    return isa_impl<To, From>::doit(*Val);
92  }
93};
94
95template <typename To, typename From> struct isa_impl_cl<To, const From*> {
96  static inline bool doit(const From *Val) {
97    assert(Val && "isa<> used on a null pointer");
98    return isa_impl<To, From>::doit(*Val);
99  }
100};
101
102template <typename To, typename From> struct isa_impl_cl<To, const From*const> {
103  static inline bool doit(const From *Val) {
104    assert(Val && "isa<> used on a null pointer");
105    return isa_impl<To, From>::doit(*Val);
106  }
107};
108
109template<typename To, typename From, typename SimpleFrom>
110struct isa_impl_wrap {
111  // When From != SimplifiedType, we can simplify the type some more by using
112  // the simplify_type template.
113  static bool doit(const From &Val) {
114    return isa_impl_wrap<To, SimpleFrom,
115      typename simplify_type<SimpleFrom>::SimpleType>::doit(
116                          simplify_type<const From>::getSimplifiedValue(Val));
117  }
118};
119
120template<typename To, typename FromTy>
121struct isa_impl_wrap<To, FromTy, FromTy> {
122  // When From == SimpleType, we are as simple as we are going to get.
123  static bool doit(const FromTy &Val) {
124    return isa_impl_cl<To,FromTy>::doit(Val);
125  }
126};
127
128// isa<X> - Return true if the parameter to the template is an instance of the
129// template type argument.  Used like this:
130//
131//  if (isa<Type>(myVal)) { ... }
132//
133template <class X, class Y>
134inline bool isa(const Y &Val) {
135  return isa_impl_wrap<X, const Y,
136                       typename simplify_type<const Y>::SimpleType>::doit(Val);
137}
138
139//===----------------------------------------------------------------------===//
140//                          cast<x> Support Templates
141//===----------------------------------------------------------------------===//
142
143template<class To, class From> struct cast_retty;
144
145
146// Calculate what type the 'cast' function should return, based on a requested
147// type of To and a source type of From.
148template<class To, class From> struct cast_retty_impl {
149  typedef To& ret_type;         // Normal case, return Ty&
150};
151template<class To, class From> struct cast_retty_impl<To, const From> {
152  typedef const To &ret_type;   // Normal case, return Ty&
153};
154
155template<class To, class From> struct cast_retty_impl<To, From*> {
156  typedef To* ret_type;         // Pointer arg case, return Ty*
157};
158
159template<class To, class From> struct cast_retty_impl<To, const From*> {
160  typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
161};
162
163template<class To, class From> struct cast_retty_impl<To, const From*const> {
164  typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
165};
166
167
168template<class To, class From, class SimpleFrom>
169struct cast_retty_wrap {
170  // When the simplified type and the from type are not the same, use the type
171  // simplifier to reduce the type, then reuse cast_retty_impl to get the
172  // resultant type.
173  typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type;
174};
175
176template<class To, class FromTy>
177struct cast_retty_wrap<To, FromTy, FromTy> {
178  // When the simplified type is equal to the from type, use it directly.
179  typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type;
180};
181
182template<class To, class From>
183struct cast_retty {
184  typedef typename cast_retty_wrap<To, From,
185                   typename simplify_type<From>::SimpleType>::ret_type ret_type;
186};
187
188// Ensure the non-simple values are converted using the simplify_type template
189// that may be specialized by smart pointers...
190//
191template<class To, class From, class SimpleFrom> struct cast_convert_val {
192  // This is not a simple type, use the template to simplify it...
193  static typename cast_retty<To, From>::ret_type doit(From &Val) {
194    return cast_convert_val<To, SimpleFrom,
195      typename simplify_type<SimpleFrom>::SimpleType>::doit(
196                          simplify_type<From>::getSimplifiedValue(Val));
197  }
198};
199
200template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
201  // This _is_ a simple type, just cast it.
202  static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) {
203    typename cast_retty<To, FromTy>::ret_type Res2
204     = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val);
205    return Res2;
206  }
207};
208
209
210
211// cast<X> - Return the argument parameter cast to the specified type.  This
212// casting operator asserts that the type is correct, so it does not return null
213// on failure.  It does not allow a null argument (use cast_or_null for that).
214// It is typically used like this:
215//
216//  cast<Instruction>(myVal)->getParent()
217//
218template <class X, class Y>
219inline typename cast_retty<X, const Y>::ret_type cast(const Y &Val) {
220  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
221  return cast_convert_val<X, const Y,
222                        typename simplify_type<const Y>::SimpleType>::doit(Val);
223}
224
225template <class X, class Y>
226inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
227  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
228  return cast_convert_val<X, Y,
229                          typename simplify_type<Y>::SimpleType>::doit(Val);
230}
231
232template <class X, class Y>
233inline typename enable_if<
234  is_same<Y, typename simplify_type<Y>::SimpleType>,
235  typename cast_retty<X, Y*>::ret_type
236>::type cast(Y *Val) {
237  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
238  return cast_convert_val<X, Y*,
239                          typename simplify_type<Y*>::SimpleType>::doit(Val);
240}
241
242// cast_or_null<X> - Functionally identical to cast, except that a null value is
243// accepted.
244//
245template <class X, class Y>
246inline typename cast_retty<X, Y*>::ret_type cast_or_null(Y *Val) {
247  if (Val == 0) return 0;
248  assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
249  return cast<X>(Val);
250}
251
252
253// dyn_cast<X> - Return the argument parameter cast to the specified type.  This
254// casting operator returns null if the argument is of the wrong type, so it can
255// be used to test for a type as well as cast if successful.  This should be
256// used in the context of an if statement like this:
257//
258//  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
259//
260
261template <class X, class Y>
262inline typename cast_retty<X, const Y>::ret_type dyn_cast(const Y &Val) {
263  return isa<X>(Val) ? cast<X>(Val) : 0;
264}
265
266template <class X, class Y>
267inline typename cast_retty<X, Y>::ret_type dyn_cast(Y &Val) {
268  return isa<X>(Val) ? cast<X>(Val) : 0;
269}
270
271template <class X, class Y>
272inline typename enable_if<
273  is_same<Y, typename simplify_type<Y>::SimpleType>,
274  typename cast_retty<X, Y*>::ret_type
275>::type dyn_cast(Y *Val) {
276  return isa<X>(Val) ? cast<X>(Val) : 0;
277}
278
279// dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null
280// value is accepted.
281//
282template <class X, class Y>
283inline typename cast_retty<X, Y*>::ret_type dyn_cast_or_null(Y *Val) {
284  return (Val && isa<X>(Val)) ? cast<X>(Val) : 0;
285}
286
287} // End llvm namespace
288
289#endif
290