1// Protocol Buffers - Google's data interchange format
2// Copyright 2008 Google Inc. All rights reserved.
3// https://developers.google.com/protocol-buffers/
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30
31#ifndef GOOGLE_PROTOBUF_UTIL_INTERNAL_STRUCTURED_OBJECTWRITER_H__
32#define GOOGLE_PROTOBUF_UTIL_INTERNAL_STRUCTURED_OBJECTWRITER_H__
33
34#include <memory>
35
36#include <google/protobuf/stubs/casts.h>
37#include <google/protobuf/stubs/common.h>
38#include <google/protobuf/util/internal/object_writer.h>
39
40// Must be included last.
41#include <google/protobuf/port_def.inc>
42
43namespace google {
44namespace protobuf {
45namespace util {
46namespace converter {
47
48// An StructuredObjectWriter is an ObjectWriter for writing
49// tree-structured data in a stream of events representing objects
50// and collections. Implementation of this interface can be used to
51// write an object stream to an in-memory structure, protobufs,
52// JSON, XML, or any other output format desired. The ObjectSource
53// interface is typically used as the source of an object stream.
54//
55// See JsonObjectWriter for a sample implementation of
56// StructuredObjectWriter and its use.
57//
58// Derived classes could be thread-unsafe.
59class PROTOBUF_EXPORT StructuredObjectWriter : public ObjectWriter {
60 public:
61 ~StructuredObjectWriter() override {}
62
63 protected:
64 // A base element class for subclasses to extend, makes tracking state easier.
65 //
66 // StructuredObjectWriter behaves as a visitor. BaseElement represents a node
67 // in the input tree. Implementation of StructuredObjectWriter should also
68 // extend BaseElement to keep track of the location in the input tree.
69 class PROTOBUF_EXPORT BaseElement {
70 public:
71 // Takes ownership of the parent Element.
72 explicit BaseElement(BaseElement* parent)
73 : parent_(parent),
74 level_(parent == nullptr ? 0 : parent->level() + 1) {}
75 virtual ~BaseElement() {}
76
77 // Releases ownership of the parent and returns a pointer to it.
78 template <typename ElementType>
79 ElementType* pop() {
80 return down_cast<ElementType*>(parent_.release());
81 }
82
83 // Returns true if this element is the root.
84 bool is_root() const { return parent_ == nullptr; }
85
86 // Returns the number of hops from this element to the root element.
87 int level() const { return level_; }
88
89 protected:
90 // Returns pointer to parent element without releasing ownership.
91 virtual BaseElement* parent() const { return parent_.get(); }
92
93 private:
94 // Pointer to the parent Element.
95 std::unique_ptr<BaseElement> parent_;
96
97 // Number of hops to the root Element.
98 // The root Element has nullptr parent_ and a level_ of 0.
99 const int level_;
100
101 GOOGLE_DISALLOW_IMPLICIT_CONSTRUCTORS(BaseElement);
102 };
103
104 StructuredObjectWriter() {}
105
106 // Returns the current element. Used for indentation and name overrides.
107 virtual BaseElement* element() = 0;
108
109 private:
110 // Do not add any data members to this class.
111 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StructuredObjectWriter);
112};
113
114} // namespace converter
115} // namespace util
116} // namespace protobuf
117} // namespace google
118
119#include <google/protobuf/port_undef.inc>
120
121#endif // GOOGLE_PROTOBUF_UTIL_INTERNAL_STRUCTURED_OBJECTWRITER_H__
122