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hash.h
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1 //
2 // Copyright 2016 Pixar
3 //
4 // Licensed under the Apache License, Version 2.0 (the "Apache License")
5 // with the following modification; you may not use this file except in
6 // compliance with the Apache License and the following modification to it:
7 // Section 6. Trademarks. is deleted and replaced with:
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9 // 6. Trademarks. This License does not grant permission to use the trade
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14 // You may obtain a copy of the Apache License at
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19 // distributed under the Apache License with the above modification is
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24 #ifndef PXR_BASE_VT_HASH_H
25 #define PXR_BASE_VT_HASH_H
26 
27 #include "pxr/pxr.h"
28 #include "pxr/base/vt/api.h"
29 #include "pxr/base/tf/hash.h"
30 #include <hboost/functional/hash.hpp>
31 #include <typeinfo>
32 #include <utility>
33 
35 
36 namespace Vt_HashDetail {
37 
38 // Issue a coding error when we attempt to hash a t.
39 VT_API void _IssueUnimplementedHashError(std::type_info const &t);
40 
41 // We make unqualified calls, intending to pick up hboost::hash_value if an
42 // overload isn't found by ADL.
43 using hboost::hash_value;
44 
45 // A constexpr function that determines hashability.
46 template <class T, class = decltype(hash_value(std::declval<T>()))>
47 constexpr bool _IsHashable(int) { return true; }
48 template <class T, class = decltype(TfHash()(std::declval<T>()))>
49 constexpr bool _IsHashable(long) { return true; }
50 template <class T>
51 constexpr bool _IsHashable(...) { return false; }
52 
53 // Hash implementations -- We're using an overload resolution ordering trick
54 // here (int vs long vs ...) so that we pick hash_value first, if possible,
55 // otherwise we do TfHash() if possible, otherwise we issue a runtime error.
56 template <class T, class = decltype(hash_value(std::declval<T>()))>
57 inline size_t
58 _HashValueImpl(T const &val, int)
59 {
60  return hash_value(val);
61 }
62 
63 template <class T, class = decltype(TfHash()(std::declval<T>()))>
64 inline size_t
65 _HashValueImpl(T const &val, long)
66 {
67  return TfHash()(val);
68 }
69 
70 template <class T>
71 inline size_t
72 _HashValueImpl(T const &val, ...)
73 {
75  return 0;
76 }
77 
78 } // Vt_HashDetail
79 
80 
81 /// A constexpr function that returns true if T is hashable via VtHashValue,
82 /// false otherwise. This is true if we can either invoke
83 /// (hboost::)hash_value() or TfHash()() on a T instance.
84 template <class T>
85 constexpr bool
87  return Vt_HashDetail::_IsHashable<T>(0);
88 }
89 
90 /// Compute a hash code for \p val by invoking (hboost::)hash_value(val) if
91 /// possible, otherwise by invoking TfHash()(val), or if neither are possible
92 /// issue a coding error and return 0.
93 template <class T>
94 size_t VtHashValue(T const &val)
95 {
96  return Vt_HashDetail::_HashValueImpl(val, 0);
97 }
98 
100 
101 #endif // PXR_BASE_VT_HASH_H
GLuint const GLfloat * val
Definition: glew.h:2794
#define VT_API
Definition: api.h:40
Definition: hash.h:366
constexpr bool VtIsHashable()
Definition: hash.h:86
PXR_NAMESPACE_CLOSE_SCOPE PXR_NAMESPACE_OPEN_SCOPE
Definition: path.h:1346
size_t VtHashValue(T const &val)
Definition: hash.h:94
#define PXR_NAMESPACE_CLOSE_SCOPE
Definition: pxr.h:91
size_t _HashValueImpl(T const &val, int)
Definition: hash.h:58
constexpr bool _IsHashable(int)
Definition: hash.h:47
size_t hash_value(const CH_ChannelRef &ref)
GLdouble GLdouble t
Definition: glew.h:1398
VT_API void _IssueUnimplementedHashError(std::type_info const &t)