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