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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:
8 //
9 // 6. Trademarks. This License does not grant permission to use the trade
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11 // and its affiliates, except as required to comply with Section 4(c) of
12 // the License and to reproduce the content of the NOTICE file.
13 //
14 // You may obtain a copy of the Apache License at
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16 // http://www.apache.org/licenses/LICENSE-2.0
17 //
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19 // distributed under the Apache License with the above modification is
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23 //
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 <typeinfo>
31 #include <utility>
32 
34 
35 namespace Vt_HashDetail {
36 
37 // Issue a coding error when we attempt to hash a t.
38 VT_API void _IssueUnimplementedHashError(std::type_info const &t);
39 
40 // A constexpr function that determines hashability.
41 template <class T, class = decltype(TfHash()(std::declval<T>()))>
42 constexpr bool _IsHashable(long) { return true; }
43 template <class T>
44 constexpr bool _IsHashable(...) { return false; }
45 
46 // Hash implementations -- We're using an overload resolution ordering trick
47 // here (long vs ...) so that we pick TfHash() if possible, otherwise
48 // we issue a runtime error.
49 template <class T, class = decltype(TfHash()(std::declval<T>()))>
50 inline size_t
51 _HashValueImpl(T const &val, long)
52 {
53  return TfHash()(val);
54 }
55 
56 template <class T>
57 inline size_t
58 _HashValueImpl(T const &val, ...)
59 {
61  return 0;
62 }
63 
64 } // Vt_HashDetail
65 
66 
67 /// A constexpr function that returns true if T is hashable via VtHashValue,
68 /// false otherwise. This is true if we can invoke TfHash()() on a T instance.
69 template <class T>
70 constexpr bool
72  return Vt_HashDetail::_IsHashable<T>(0);
73 }
74 
75 /// Compute a hash code for \p val by invoking TfHash()(val) or when not
76 /// possible issue a coding error and return 0.
77 template <class T>
78 size_t VtHashValue(T const &val)
79 {
80  return Vt_HashDetail::_HashValueImpl(val, 0);
81 }
82 
84 
85 #endif // PXR_BASE_VT_HASH_H
constexpr bool _IsHashable(long)
Definition: hash.h:42
#define VT_API
Definition: api.h:40
Definition: hash.h:477
size_t _HashValueImpl(T const &val, long)
Definition: hash.h:51
constexpr bool VtIsHashable()
Definition: hash.h:71
GLdouble t
Definition: glad.h:2397
PXR_NAMESPACE_CLOSE_SCOPE PXR_NAMESPACE_OPEN_SCOPE
Definition: path.h:1432
size_t VtHashValue(T const &val)
Definition: hash.h:78
GLuint GLfloat * val
Definition: glcorearb.h:1608
#define PXR_NAMESPACE_CLOSE_SCOPE
Definition: pxr.h:91
VT_API void _IssueUnimplementedHashError(std::type_info const &t)