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