clang  9.0.0svn
TypeVisitor.h
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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
RetTy VisitType(const Type *)
Method called if ImpClass doesn&#39;t provide specific handler for some type class.
Definition: TypeVisitor.h:87
C Language Family Type Representation.
The base class of the type hierarchy.
Definition: Type.h:1414
RetTy Visit(const Type *T)
Performs the operation associated with this visitor object.
Definition: TypeVisitor.h:68
An operation on a type.
Definition: TypeVisitor.h:64
TypeClass getTypeClass() const
Definition: Type.h:1820
Dataflow Directional Tag Classes.