fakeRttiSupport.hpp revision 7923:1573e72240b9 
1/*
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24
25#ifndef SHARE_VM_UTILITIES_FAKERTTISUPPORT_HPP
26#define SHARE_VM_UTILITIES_FAKERTTISUPPORT_HPP
27
28#include "utilities/globalDefinitions.hpp"
29#include "utilities/debug.hpp"
30
31// Provides support for checked downcasts in a hierarchy of classes.
32// The base class provides a member of this type, specialized on that
33// base class and an associated tag type.  Tags are small non-negative
34// integer values uniquely associated with distinct classes in the
35// hierarchy.  A tag type is often an enum type.
36//
37// The concrete class specifies the concrete tag.
38//
39// The tag set specifies the set of classes in the derivation
40// sequence.  Classes in the derivation sequence add their associated
41// tag during construction.  Given the tag associated with a class, an
42// object is an instance of that class if the tag is included in the
43// object's set of recorded tags.
44//
45// A tag T is present in a tag set if the T'th bit of the tag set is
46// one.
47//
48// Note: The representation of a tag set being uintx sets an upper
49// bound on the size of a class hierarchy this utility can be used
50// with.
51template<typename T, typename TagType>
52class FakeRttiSupport VALUE_OBJ_CLASS_SPEC {
53public:
54  // Construct with the indicated concrete tag, and include the
55  // concrete tag in the associated tag set.
56  explicit FakeRttiSupport(TagType concrete_tag) :
57    _tag_set(tag_bit(concrete_tag)), _concrete_tag(concrete_tag) { }
58
59  // Construct with the indicated concrete tag and tag set.
60  // Note: This constructor is public only to allow clients to set up
61  // "unusual" (or perhaps buggy) fake RTTI configurations.
62  FakeRttiSupport(TagType concrete_tag, uintx tag_set) :
63    _tag_set(tag_set), _concrete_tag(validate_tag(concrete_tag)) { }
64
65  // Get the concrete tag.
66  TagType concrete_tag() const { return _concrete_tag; }
67
68  // Test whether tag is in the tag set.
69  bool has_tag(TagType tag) const {
70    return (_tag_set & tag_bit(tag)) != 0;
71  }
72
73  // Return a new support object which is the same as this, except tag
74  // has been added to the tag set.  The tag must not already be
75  // present in the tag set.
76  FakeRttiSupport add_tag(TagType tag) const {
77    uintx tbit = tag_bit(tag);
78    assert((_tag_set & tbit) == 0,
79           err_msg("Tag " UINTX_FORMAT " is already present in tag set: " UINTX_FORMAT,
80                   (uintx)tag, _tag_set));
81    return FakeRttiSupport(_concrete_tag, _tag_set | tbit);
82  }
83
84private:
85  uintx _tag_set;
86  TagType _concrete_tag;
87
88  static uintx tag_bit(TagType tag) {
89    return ((uintx)1) << validate_tag(tag);
90  }
91
92  static TagType validate_tag(uintx tag) {
93    // Type of tag is not TagType to dodge useless MacOSX compiler warning.
94    assert(tag < (sizeof(uintx) * BitsPerByte),
95           err_msg("Tag " UINTX_FORMAT " is too large", tag));
96    return static_cast<TagType>(tag);
97  }
98};
99
100#endif // include guard
101