1 // Copyright 2018 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef BASE_COMPONENT_EXPORT_H_
6 #define BASE_COMPONENT_EXPORT_H_
8 #include "build/build_config.h"
10 // Used to annotate symbols which are exported by the component named
11 // |component|. Note that this only does the right thing if the corresponding
12 // component target's sources are compiled with |IS_$component_IMPL| defined
15 // class COMPONENT_EXPORT(FOO) Bar {};
17 // If IS_FOO_IMPL=1 at compile time, then Bar will be annotated using the
18 // COMPONENT_EXPORT_ANNOTATION macro defined below. Otherwise it will be
19 // annotated using the COMPONENT_IMPORT_ANNOTATION macro.
20 #define COMPONENT_EXPORT(component) \
21 COMPONENT_MACRO_CONDITIONAL_(IS_##component##_IMPL, \
22 COMPONENT_EXPORT_ANNOTATION, \
23 COMPONENT_IMPORT_ANNOTATION)
25 // Indicates whether the current compilation unit is being compiled as part of
26 // the implementation of the component named |component|. Expands to |1| if
27 // |IS_$component_IMPL| is defined as |1|; expands to |0| otherwise.
29 // Note in particular that if |IS_$component_IMPL| is not defined at all, it is
30 // still fine to test INSIDE_COMPONENT_IMPL(component), which expands to |0| as
32 #define INSIDE_COMPONENT_IMPL(component) \
33 COMPONENT_MACRO_CONDITIONAL_(IS_##component##_IMPL, 1, 0)
35 // Compiler-specific macros to annotate for export or import of a symbol. No-op
36 // in non-component builds. These should not see much if any direct use.
37 // Instead use the COMPONENT_EXPORT macro defined above.
38 #if defined(COMPONENT_BUILD)
40 #define COMPONENT_EXPORT_ANNOTATION __declspec(dllexport)
41 #define COMPONENT_IMPORT_ANNOTATION __declspec(dllimport)
42 #else // defined(WIN32)
43 #define COMPONENT_EXPORT_ANNOTATION __attribute__((visibility("default")))
44 #define COMPONENT_IMPORT_ANNOTATION
45 #endif // defined(WIN32)
46 #else // defined(COMPONENT_BUILD)
47 #define COMPONENT_EXPORT_ANNOTATION
48 #define COMPONENT_IMPORT_ANNOTATION
49 #endif // defined(COMPONENT_BUILD)
51 // Below this point are several internal utility macros used for the
52 // implementation of the above macros. Not intended for external use.
54 // Helper for conditional expansion to one of two token strings. If |condition|
55 // expands to |1| then this macro expands to |consequent|; otherwise it expands
57 #define COMPONENT_MACRO_CONDITIONAL_(condition, consequent, alternate) \
58 COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_( \
59 COMPONENT_MACRO_CONDITIONAL_COMMA_(condition), consequent, alternate)
61 // Expands to a comma (,) iff its first argument expands to |1|. Used in
62 // conjunction with |COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_()|, as the presence
63 // or absense of an extra comma can be used to conditionally shift subsequent
64 // argument positions and thus influence which argument is selected.
65 #define COMPONENT_MACRO_CONDITIONAL_COMMA_(...) \
66 COMPONENT_MACRO_CONDITIONAL_COMMA_IMPL_(__VA_ARGS__,)
67 #define COMPONENT_MACRO_CONDITIONAL_COMMA_IMPL_(x, ...) \
68 COMPONENT_MACRO_CONDITIONAL_COMMA_##x##_
69 #define COMPONENT_MACRO_CONDITIONAL_COMMA_1_ ,
71 // Helper which simply selects its third argument. Used in conjunction with
72 // |COMPONENT_MACRO_CONDITIONAL_COMMA_()| above to implement conditional macro
74 #define COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_(...) \
75 COMPONENT_MACRO_EXPAND_( \
76 COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_IMPL_(__VA_ARGS__))
77 #define COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_IMPL_(a, b, c, ...) c
79 // Helper to work around MSVC quirkiness wherein a macro expansion like |,|
80 // within a parameter list will be treated as a single macro argument. This is
81 // needed to ensure that |COMPONENT_MACRO_CONDITIONAL_COMMA_()| above can expand
82 // to multiple separate positional arguments in the affirmative case, thus
83 // elliciting the desired conditional behavior with
84 // |COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_()|.
85 #define COMPONENT_MACRO_EXPAND_(x) x
87 #endif // BASE_COMPONENT_EXPORT_H_