Casting.h revision 8b70b78ba489b090d9866e6a4084ab1e8613b527
1//===-- Support/Casting.h - Allow flexible, checked, casts ------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source 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 SUPPORT_CASTING_H 16#define SUPPORT_CASTING_H 17 18namespace llvm { 19 20//===----------------------------------------------------------------------===// 21// isa<x> Support Templates 22//===----------------------------------------------------------------------===// 23 24template<typename FromCl> struct isa_impl_cl; 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 45// isa<X> - Return true if the parameter to the template is an instance of the 46// template type argument. Used like this: 47// 48// if (isa<Type*>(myVal)) { ... } 49// 50template <typename To, typename From> 51inline bool isa_impl(const From &Val) { 52 return To::classof(&Val); 53} 54 55template<typename To, typename From, typename SimpleType> 56struct isa_impl_wrap { 57 // When From != SimplifiedType, we can simplify the type some more by using 58 // the simplify_type template. 59 static bool doit(const From &Val) { 60 return isa_impl_cl<const SimpleType>::template 61 isa<To>(simplify_type<const From>::getSimplifiedValue(Val)); 62 } 63}; 64 65template<typename To, typename FromTy> 66struct isa_impl_wrap<To, const FromTy, const FromTy> { 67 // When From == SimpleType, we are as simple as we are going to get. 68 static bool doit(const FromTy &Val) { 69 return isa_impl<To,FromTy>(Val); 70 } 71}; 72 73// isa_impl_cl - Use class partial specialization to transform types to a single 74// canonical form for isa_impl. 75// 76template<typename FromCl> 77struct isa_impl_cl { 78 template<class ToCl> 79 static bool isa(const FromCl &Val) { 80 return isa_impl_wrap<ToCl,const FromCl, 81 typename simplify_type<const FromCl>::SimpleType>::doit(Val); 82 } 83}; 84 85// Specialization used to strip const qualifiers off of the FromCl type... 86template<typename FromCl> 87struct isa_impl_cl<const FromCl> { 88 template<class ToCl> 89 static bool isa(const FromCl &Val) { 90 return isa_impl_cl<FromCl>::template isa<ToCl>(Val); 91 } 92}; 93 94// Define pointer traits in terms of base traits... 95template<class FromCl> 96struct isa_impl_cl<FromCl*> { 97 template<class ToCl> 98 static bool isa(FromCl *Val) { 99 return isa_impl_cl<FromCl>::template isa<ToCl>(*Val); 100 } 101}; 102 103// Define reference traits in terms of base traits... 104template<class FromCl> 105struct isa_impl_cl<FromCl&> { 106 template<class ToCl> 107 static bool isa(FromCl &Val) { 108 return isa_impl_cl<FromCl>::template isa<ToCl>(&Val); 109 } 110}; 111 112template <class X, class Y> 113inline bool isa(const Y &Val) { 114 return isa_impl_cl<Y>::template isa<X>(Val); 115} 116 117//===----------------------------------------------------------------------===// 118// cast<x> Support Templates 119//===----------------------------------------------------------------------===// 120 121template<class To, class From> struct cast_retty; 122 123 124// Calculate what type the 'cast' function should return, based on a requested 125// type of To and a source type of From. 126template<class To, class From> struct cast_retty_impl { 127 typedef To& ret_type; // Normal case, return Ty& 128}; 129template<class To, class From> struct cast_retty_impl<To, const From> { 130 typedef const To &ret_type; // Normal case, return Ty& 131}; 132 133template<class To, class From> struct cast_retty_impl<To, From*> { 134 typedef To* ret_type; // Pointer arg case, return Ty* 135}; 136 137template<class To, class From> struct cast_retty_impl<To, const From*> { 138 typedef const To* ret_type; // Constant pointer arg case, return const Ty* 139}; 140 141template<class To, class From> struct cast_retty_impl<To, const From*const> { 142 typedef const To* ret_type; // Constant pointer arg case, return const Ty* 143}; 144 145 146template<class To, class From, class SimpleFrom> 147struct cast_retty_wrap { 148 // When the simplified type and the from type are not the same, use the type 149 // simplifier to reduce the type, then reuse cast_retty_impl to get the 150 // resultant type. 151 typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type; 152}; 153 154template<class To, class FromTy> 155struct cast_retty_wrap<To, FromTy, FromTy> { 156 // When the simplified type is equal to the from type, use it directly. 157 typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type; 158}; 159 160template<class To, class From> 161struct cast_retty { 162 typedef typename cast_retty_wrap<To, From, 163 typename simplify_type<From>::SimpleType>::ret_type ret_type; 164}; 165 166// Ensure the non-simple values are converted using the simplify_type template 167// that may be specialized by smart pointers... 168// 169template<class To, class From, class SimpleFrom> struct cast_convert_val { 170 // This is not a simple type, use the template to simplify it... 171 static typename cast_retty<To, From>::ret_type doit(const From &Val) { 172 return cast_convert_val<To, SimpleFrom, 173 typename simplify_type<SimpleFrom>::SimpleType>::doit( 174 simplify_type<From>::getSimplifiedValue(Val)); 175 } 176}; 177 178template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> { 179 // This _is_ a simple type, just cast it. 180 static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) { 181 return reinterpret_cast<typename cast_retty<To, FromTy>::ret_type>( 182 const_cast<FromTy&>(Val)); 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. But it will correctly return NULL when the input is NULL. 191// 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(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, Y>(Val) : 0; 232} 233 234 235#ifdef DEBUG_CAST_OPERATORS 236#include <iostream> 237 238struct bar { 239 bar() {} 240private: 241 bar(const bar &); 242}; 243struct foo { 244 void ext() const; 245 /* static bool classof(const bar *X) { 246 cerr << "Classof: " << X << "\n"; 247 return true; 248 }*/ 249}; 250 251template <> inline bool isa_impl<foo,bar>(const bar &Val) { 252 cerr << "Classof: " << &Val << "\n"; 253 return true; 254} 255 256 257bar *fub(); 258void test(bar &B1, const bar *B2) { 259 // test various configurations of const 260 const bar &B3 = B1; 261 const bar *const B4 = B2; 262 263 // test isa 264 if (!isa<foo>(B1)) return; 265 if (!isa<foo>(B2)) return; 266 if (!isa<foo>(B3)) return; 267 if (!isa<foo>(B4)) return; 268 269 // test cast 270 foo &F1 = cast<foo>(B1); 271 const foo *F3 = cast<foo>(B2); 272 const foo *F4 = cast<foo>(B2); 273 const foo &F8 = cast<foo>(B3); 274 const foo *F9 = cast<foo>(B4); 275 foo *F10 = cast<foo>(fub()); 276 277 // test cast_or_null 278 const foo *F11 = cast_or_null<foo>(B2); 279 const foo *F12 = cast_or_null<foo>(B2); 280 const foo *F13 = cast_or_null<foo>(B4); 281 const foo *F14 = cast_or_null<foo>(fub()); // Shouldn't print. 282 283 // These lines are errors... 284 //foo *F20 = cast<foo>(B2); // Yields const foo* 285 //foo &F21 = cast<foo>(B3); // Yields const foo& 286 //foo *F22 = cast<foo>(B4); // Yields const foo* 287 //foo &F23 = cast_or_null<foo>(B1); 288 //const foo &F24 = cast_or_null<foo>(B3); 289} 290 291bar *fub() { return 0; } 292void main() { 293 bar B; 294 test(B, &B); 295} 296 297#endif 298 299} // End llvm namespace 300 301#endif 302