Casting.h revision 8b8fa7b2f403ae2f342413239c4151e075022c97
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 const From SimpleType; 40 static SimpleType &getSimplifiedValue(const From &Val) { 41 return simplify_type<From>::getSimplifiedValue(static_cast<From&>(Val)); 42 } 43}; 44 45// The core of the implementation of isa<X> is here; To and From should be 46// the names of classes. This template can be specialized to customize the 47// implementation of isa<> without rewriting it from scratch. 48template <typename To, typename From, typename Enabler = void> 49struct isa_impl { 50 static inline bool doit(const From &Val) { 51 return To::classof(&Val); 52 } 53}; 54 55/// \brief Always allow upcasts, and perform no dynamic check for them. 56template <typename To, typename From> 57struct isa_impl<To, From, 58 typename llvm::enable_if_c< 59 llvm::is_base_of<To, From>::value 60 >::type 61 > { 62 static inline bool doit(const From &) { return true; } 63}; 64 65template <typename To, typename From> struct isa_impl_cl { 66 static inline bool doit(const From &Val) { 67 return isa_impl<To, From>::doit(Val); 68 } 69}; 70 71template <typename To, typename From> struct isa_impl_cl<To, const From> { 72 static inline bool doit(const From &Val) { 73 return isa_impl<To, From>::doit(Val); 74 } 75}; 76 77template <typename To, typename From> struct isa_impl_cl<To, From*> { 78 static inline bool doit(const From *Val) { 79 assert(Val && "isa<> used on a null pointer"); 80 return isa_impl<To, From>::doit(*Val); 81 } 82}; 83 84template <typename To, typename From> struct isa_impl_cl<To, const From*> { 85 static inline bool doit(const From *Val) { 86 assert(Val && "isa<> used on a null pointer"); 87 return isa_impl<To, From>::doit(*Val); 88 } 89}; 90 91template <typename To, typename From> struct isa_impl_cl<To, const From*const> { 92 static inline bool doit(const From *Val) { 93 assert(Val && "isa<> used on a null pointer"); 94 return isa_impl<To, From>::doit(*Val); 95 } 96}; 97 98template<typename To, typename From, typename SimpleFrom> 99struct isa_impl_wrap { 100 // When From != SimplifiedType, we can simplify the type some more by using 101 // the simplify_type template. 102 static bool doit(const From &Val) { 103 return isa_impl_wrap<To, SimpleFrom, 104 typename simplify_type<SimpleFrom>::SimpleType>::doit( 105 simplify_type<From>::getSimplifiedValue(Val)); 106 } 107}; 108 109template<typename To, typename FromTy> 110struct isa_impl_wrap<To, FromTy, FromTy> { 111 // When From == SimpleType, we are as simple as we are going to get. 112 static bool doit(const FromTy &Val) { 113 return isa_impl_cl<To,FromTy>::doit(Val); 114 } 115}; 116 117// isa<X> - Return true if the parameter to the template is an instance of the 118// template type argument. Used like this: 119// 120// if (isa<Type>(myVal)) { ... } 121// 122template <class X, class Y> 123inline bool isa(const Y &Val) { 124 return isa_impl_wrap<X, Y, typename simplify_type<Y>::SimpleType>::doit(Val); 125} 126 127//===----------------------------------------------------------------------===// 128// cast<x> Support Templates 129//===----------------------------------------------------------------------===// 130 131template<class To, class From> struct cast_retty; 132 133 134// Calculate what type the 'cast' function should return, based on a requested 135// type of To and a source type of From. 136template<class To, class From> struct cast_retty_impl { 137 typedef To& ret_type; // Normal case, return Ty& 138}; 139template<class To, class From> struct cast_retty_impl<To, const From> { 140 typedef const To &ret_type; // Normal case, return Ty& 141}; 142 143template<class To, class From> struct cast_retty_impl<To, From*> { 144 typedef To* ret_type; // Pointer arg case, return Ty* 145}; 146 147template<class To, class From> struct cast_retty_impl<To, const From*> { 148 typedef const To* ret_type; // Constant pointer arg case, return const Ty* 149}; 150 151template<class To, class From> struct cast_retty_impl<To, const From*const> { 152 typedef const To* ret_type; // Constant pointer arg case, return const Ty* 153}; 154 155 156template<class To, class From, class SimpleFrom> 157struct cast_retty_wrap { 158 // When the simplified type and the from type are not the same, use the type 159 // simplifier to reduce the type, then reuse cast_retty_impl to get the 160 // resultant type. 161 typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type; 162}; 163 164template<class To, class FromTy> 165struct cast_retty_wrap<To, FromTy, FromTy> { 166 // When the simplified type is equal to the from type, use it directly. 167 typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type; 168}; 169 170template<class To, class From> 171struct cast_retty { 172 typedef typename cast_retty_wrap<To, From, 173 typename simplify_type<From>::SimpleType>::ret_type ret_type; 174}; 175 176// Ensure the non-simple values are converted using the simplify_type template 177// that may be specialized by smart pointers... 178// 179template<class To, class From, class SimpleFrom> struct cast_convert_val { 180 // This is not a simple type, use the template to simplify it... 181 static typename cast_retty<To, From>::ret_type doit(const From &Val) { 182 return cast_convert_val<To, SimpleFrom, 183 typename simplify_type<SimpleFrom>::SimpleType>::doit( 184 simplify_type<From>::getSimplifiedValue(Val)); 185 } 186}; 187 188template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> { 189 // This _is_ a simple type, just cast it. 190 static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) { 191 typename cast_retty<To, FromTy>::ret_type Res2 192 = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val); 193 return Res2; 194 } 195}; 196 197 198 199// cast<X> - Return the argument parameter cast to the specified type. This 200// casting operator asserts that the type is correct, so it does not return null 201// on failure. It does not allow a null argument (use cast_or_null for that). 202// It is typically used like this: 203// 204// cast<Instruction>(myVal)->getParent() 205// 206template <class X, class Y> 207inline typename cast_retty<X, Y>::ret_type cast(const Y &Val) { 208 assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!"); 209 return cast_convert_val<X, Y, 210 typename simplify_type<Y>::SimpleType>::doit(Val); 211} 212 213// cast_or_null<X> - Functionally identical to cast, except that a null value is 214// accepted. 215// 216template <class X, class Y> 217inline typename cast_retty<X, Y*>::ret_type cast_or_null(Y *Val) { 218 if (Val == 0) return 0; 219 assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!"); 220 return cast<X>(Val); 221} 222 223 224// dyn_cast<X> - Return the argument parameter cast to the specified type. This 225// casting operator returns null if the argument is of the wrong type, so it can 226// be used to test for a type as well as cast if successful. This should be 227// used in the context of an if statement like this: 228// 229// if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... } 230// 231 232template <class X, class Y> 233inline typename cast_retty<X, Y>::ret_type dyn_cast(const Y &Val) { 234 return isa<X>(Val) ? cast<X, Y>(Val) : 0; 235} 236 237// dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null 238// value is accepted. 239// 240template <class X, class Y> 241inline typename cast_retty<X, Y*>::ret_type dyn_cast_or_null(Y *Val) { 242 return (Val && isa<X>(Val)) ? cast<X>(Val) : 0; 243} 244 245} // End llvm namespace 246 247#endif 248