| 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 | |
| 18 | namespace 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. |
| 63 | template<typename ImplClass, typename RetTy=void> |
| 64 | class TypeVisitor { |
| 65 | public: |
| 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.def" |
| 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.def" |
| 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 |