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77 lines
3.6 KiB
C
77 lines
3.6 KiB
C
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// Copyright 2018 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_COMPONENT_EXPORT_H_
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#define BASE_COMPONENT_EXPORT_H_
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// Used to annotate symbols which are exported by the component named
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// |component|. Note that this only does the right thing if the corresponding
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// component target's sources are compiled with |IS_$component_IMPL| defined
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// as 1. For example:
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//
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// class COMPONENT_EXPORT(FOO) Bar {};
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//
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// If IS_FOO_IMPL=1 at compile time, then Bar will be annotated using the
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// COMPONENT_EXPORT_ANNOTATION macro defined below. Otherwise it will be
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// annotated using the COMPONENT_IMPORT_ANNOTATION macro.
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#define COMPONENT_EXPORT(component) \
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COMPONENT_MACRO_CONDITIONAL_(IS_##component##_IMPL, \
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COMPONENT_EXPORT_ANNOTATION, \
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COMPONENT_IMPORT_ANNOTATION)
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// Indicates whether the current compilation unit is being compiled as part of
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// the implementation of the component named |component|. Expands to |1| if
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// |IS_$component_IMPL| is defined as |1|; expands to |0| otherwise.
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//
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// Note in particular that if |IS_$component_IMPL| is not defined at all, it is
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// still fine to test INSIDE_COMPONENT_IMPL(component), which expands to |0| as
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// expected.
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#define INSIDE_COMPONENT_IMPL(component) \
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COMPONENT_MACRO_CONDITIONAL_(IS_##component##_IMPL, 1, 0)
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// Compiler-specific macros to annotate for export or import of a symbol. No-op
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// in non-component builds. These should not see much if any direct use.
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// Instead use the COMPONENT_EXPORT macro defined above.
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#if defined(COMPONENT_BUILD)
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#if defined(WIN32)
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#define COMPONENT_EXPORT_ANNOTATION __declspec(dllexport)
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#define COMPONENT_IMPORT_ANNOTATION __declspec(dllimport)
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#else // defined(WIN32)
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#define COMPONENT_EXPORT_ANNOTATION __attribute__((visibility("default")))
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#define COMPONENT_IMPORT_ANNOTATION
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#endif // defined(WIN32)
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#else // defined(COMPONENT_BUILD)
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#define COMPONENT_EXPORT_ANNOTATION
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#define COMPONENT_IMPORT_ANNOTATION
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#endif // defined(COMPONENT_BUILD)
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// Below this point are several internal utility macros used for the
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// implementation of the above macros. Not intended for external use.
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// Helper for conditional expansion to one of two token strings. If |condition|
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// expands to |1| then this macro expands to |consequent|; otherwise it expands
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// to |alternate|.
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#define COMPONENT_MACRO_CONDITIONAL_(condition, consequent, alternate) \
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COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_( \
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COMPONENT_MACRO_CONDITIONAL_COMMA_(condition), consequent, alternate)
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// Expands to a comma (,) iff its first argument expands to |1|. Used in
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// conjunction with |COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_()|, as the presence
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// or absense of an extra comma can be used to conditionally shift subsequent
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// argument positions and thus influence which argument is selected.
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#define COMPONENT_MACRO_CONDITIONAL_COMMA_(...) \
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COMPONENT_MACRO_CONDITIONAL_COMMA_IMPL_(__VA_ARGS__,)
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#define COMPONENT_MACRO_CONDITIONAL_COMMA_IMPL_(x, ...) \
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COMPONENT_MACRO_CONDITIONAL_COMMA_##x##_
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#define COMPONENT_MACRO_CONDITIONAL_COMMA_1_ ,
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// Helper which simply selects its third argument. Used in conjunction with
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// |COMPONENT_MACRO_CONDITIONAL_COMMA_()| above to implement conditional macro
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// expansion.
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#define COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_(...) \
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COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_IMPL_(__VA_ARGS__)
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#define COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_IMPL_(a, b, c, ...) c
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#endif // BASE_COMPONENT_EXPORT_H_
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