1//===--- TypeVisitor.h - Visitor for Type subclasses ------------*- 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 defines the TypeVisitor interface. 10// 11//===----------------------------------------------------------------------===// 12 13#ifndef LLVM_CLANG_AST_TYPEVISITOR_H 14#define LLVM_CLANG_AST_TYPEVISITOR_H 15 16#include "clang/AST/Type.h" 17 18namespace clang { 19 20#define DISPATCH(CLASS) \ 21 return static_cast<ImplClass*>(this)-> \ 22 Visit##CLASS(static_cast<const CLASS*>(T)) 23 24/// An operation on a type. 25/// 26/// \tparam ImplClass Class implementing the operation. Must be inherited from 27/// TypeVisitor. 28/// \tparam RetTy %Type of result produced by the operation. 29/// 30/// The class implements polymorphic operation on an object of type derived 31/// from Type. The operation is performed by calling method Visit. It then 32/// dispatches the call to function \c VisitFooType, if actual argument type 33/// is \c FooType. 34/// 35/// The class implements static polymorphism using Curiously Recurring 36/// Template Pattern. It is designed to be a base class for some concrete 37/// class: 38/// 39/// \code 40/// class SomeVisitor : public TypeVisitor<SomeVisitor,sometype> { ... }; 41/// ... 42/// Type *atype = ... 43/// ... 44/// SomeVisitor avisitor; 45/// sometype result = avisitor.Visit(atype); 46/// \endcode 47/// 48/// Actual treatment is made by methods of the derived class, TypeVisitor only 49/// dispatches call to the appropriate method. If the implementation class 50/// \c ImplClass provides specific action for some type, say 51/// \c ConstantArrayType, it should define method 52/// <tt>VisitConstantArrayType(const ConstantArrayType*)</tt>. Otherwise 53/// \c TypeVisitor dispatches call to the method that handles parent type. In 54/// this example handlers are tried in the sequence: 55/// 56/// \li <tt>ImplClass::VisitConstantArrayType(const ConstantArrayType*)</tt> 57/// \li <tt>ImplClass::VisitArrayType(const ArrayType*)</tt> 58/// \li <tt>ImplClass::VisitType(const Type*)</tt> 59/// \li <tt>TypeVisitor::VisitType(const Type*)</tt> 60/// 61/// The first function of this sequence that is defined will handle object of 62/// type \c ConstantArrayType. 63template<typename ImplClass, typename RetTy=void> 64class TypeVisitor { 65public: 66 67 /// Performs the operation associated with this visitor object. 68 RetTy Visit(const Type *T) { 69 // Top switch stmt: dispatch to VisitFooType for each FooType. 70 switch (T->getTypeClass()) { 71#define ABSTRACT_TYPE(CLASS, PARENT) 72#define TYPE(CLASS, PARENT) case Type::CLASS: DISPATCH(CLASS##Type); 73#include "clang/AST/TypeNodes.inc" 74 } 75 llvm_unreachable("Unknown type class!"); 76 } 77 78 // If the implementation chooses not to implement a certain visit method, fall 79 // back on superclass. 80#define TYPE(CLASS, PARENT) RetTy Visit##CLASS##Type(const CLASS##Type *T) { \ 81 DISPATCH(PARENT); \ 82} 83#include "clang/AST/TypeNodes.inc" 84 85 /// Method called if \c ImpClass doesn't provide specific handler 86 /// for some type class. 87 RetTy VisitType(const Type*) { return RetTy(); } 88}; 89 90#undef DISPATCH 91 92} // end namespace clang 93 94#endif 95