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#ifndef _SHARED_PTR_H
36#include <google/protobuf/stubs/shared_ptr.h>
37#endif
38
39#include <google/protobuf/stubs/casts.h>
40#include <google/protobuf/stubs/common.h>
41#include <google/protobuf/util/internal/object_writer.h>
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 LIBPROTOBUF_EXPORT StructuredObjectWriter : public ObjectWriter {
60 public:
61  virtual ~StructuredObjectWriter() {}
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 LIBPROTOBUF_EXPORT BaseElement {
70   public:
71    // Takes ownership of the parent Element.
72    explicit BaseElement(BaseElement* parent)
73        : parent_(parent), level_(parent == NULL ? 0 : parent->level() + 1) {}
74    virtual ~BaseElement() {}
75
76    // Releases ownership of the parent and returns a pointer to it.
77    template <typename ElementType>
78    ElementType* pop() {
79      return down_cast<ElementType*>(parent_.release());
80    }
81
82    // Returns true if this element is the root.
83    bool is_root() const { return parent_ == NULL; }
84
85    // Returns the number of hops from this element to the root element.
86    int level() const { return level_; }
87
88   protected:
89    // Returns pointer to parent element without releasing ownership.
90    virtual BaseElement* parent() const { return parent_.get(); }
91
92   private:
93    // Pointer to the parent Element.
94    google::protobuf::scoped_ptr<BaseElement> parent_;
95
96    // Number of hops to the root Element.
97    // The root Element has NULL parent_ and a level_ of 0.
98    const int level_;
99
100    GOOGLE_DISALLOW_IMPLICIT_CONSTRUCTORS(BaseElement);
101  };
102
103  StructuredObjectWriter() {}
104
105  // Returns the current element. Used for indentation and name overrides.
106  virtual BaseElement* element() = 0;
107
108 private:
109  // Do not add any data members to this class.
110  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StructuredObjectWriter);
111};
112
113}  // namespace converter
114}  // namespace util
115}  // namespace protobuf
116
117}  // namespace google
118#endif  // GOOGLE_PROTOBUF_UTIL_CONVERTER_STRUCTURED_OBJECTWRITER_H__
119