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