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ImathNamespace.h
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1 //
2 // SPDX-License-Identifier: BSD-3-Clause
3 // Copyright Contributors to the OpenEXR Project.
4 //
5 
6 //
7 // The Imath library namespace
8 //
9 // The purpose of this file is to make it possible to specify an
10 // IMATH_INTERNAL_NAMESPACE as a preprocessor definition and have all of the
11 // Imath symbols defined within that namespace rather than the standard
12 // Imath namespace. Those symbols are made available to client code through
13 // the IMATH_NAMESPACE in addition to the IMATH_INTERNAL_NAMESPACE.
14 //
15 // To ensure source code compatibility, the IMATH_NAMESPACE defaults to Imath
16 // and then "using namespace IMATH_INTERNAL_NAMESPACE;" brings all of the
17 // declarations from the IMATH_INTERNAL_NAMESPACE into the IMATH_NAMESPACE.
18 // This means that client code can continue to use syntax like Imath::V3f,
19 // but at link time it will resolve to a mangled symbol based on the
20 // IMATH_INTERNAL_NAMESPACE.
21 //
22 // As an example, if one needed to build against a newer version of Imath and
23 // have it run alongside an older version in the same application, it is now
24 // possible to use an internal namespace to prevent collisions between the
25 // older versions of Imath symbols and the newer ones. To do this, the
26 // following could be defined at build time:
27 //
28 // IMATH_INTERNAL_NAMESPACE = Imath_v2
29 //
30 // This means that declarations inside Imath headers look like this (after
31 // the preprocessor has done its work):
32 //
33 // namespace Imath_v2 {
34 // ...
35 // class declarations
36 // ...
37 // }
38 //
39 // namespace Imath {
40 // using namespace Imath_v2;
41 // }
42 //
43 
44 #ifndef INCLUDED_IMATHNAMESPACE_H
45 #define INCLUDED_IMATHNAMESPACE_H
46 
47 /// @cond Doxygen_Suppress
48 
49 #include "ImathConfig.h"
50 
51 #ifndef IMATH_NAMESPACE
52 # define IMATH_NAMESPACE Imath
53 #endif
54 
55 #ifndef IMATH_INTERNAL_NAMESPACE
56 # define IMATH_INTERNAL_NAMESPACE IMATH_NAMESPACE
57 #endif
58 
59 #ifdef __cplusplus
60 
61 //
62 // We need to be sure that we import the internal namespace into the public one.
63 // To do this, we use the small bit of code below which initially defines
64 // IMATH_INTERNAL_NAMESPACE (so it can be referenced) and then defines
65 // IMATH_NAMESPACE and pulls the internal symbols into the public
66 // namespace.
67 //
68 
70 {}
71 namespace IMATH_NAMESPACE
72 {
73 using namespace IMATH_INTERNAL_NAMESPACE;
74 }
75 
76 //
77 // There are identical pairs of HEADER/SOURCE ENTER/EXIT macros so that
78 // future extension to the namespace mechanism is possible without changing
79 // project source code.
80 //
81 
82 #define IMATH_INTERNAL_NAMESPACE_HEADER_ENTER \
83  namespace IMATH_INTERNAL_NAMESPACE \
84  {
85 #define IMATH_INTERNAL_NAMESPACE_HEADER_EXIT }
86 
87 #define IMATH_INTERNAL_NAMESPACE_SOURCE_ENTER \
88  namespace IMATH_INTERNAL_NAMESPACE \
89  {
90 #define IMATH_INTERNAL_NAMESPACE_SOURCE_EXIT }
91 
92 #endif // __cplusplus
93 
94 /// @endcond
95 
96 #endif /* INCLUDED_IMATHNAMESPACE_H */
#define IMATH_INTERNAL_NAMESPACE
Definition: ImathConfig.h:36
#define IMATH_NAMESPACE
Definition: ImathConfig.h:40