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      1 // Copyright 2014 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.
      4 
      5 #ifndef MOJO_PUBLIC_C_SYSTEM_MACROS_H_
      6 #define MOJO_PUBLIC_C_SYSTEM_MACROS_H_
      7 
      8 #include <stddef.h>
      9 
     10 // Annotate a variable indicating it's okay if it's unused.
     11 // Use like:
     12 //   int x MOJO_ALLOW_UNUSED = ...;
     13 #if defined(__GNUC__)
     14 #define MOJO_ALLOW_UNUSED __attribute__((unused))
     15 #else
     16 #define MOJO_ALLOW_UNUSED
     17 #endif
     18 
     19 // Annotate a function indicating that the caller must examine the return value.
     20 // Use like:
     21 //   int foo() MOJO_WARN_UNUSED_RESULT;
     22 // Note that it can only be used on the prototype, and not the definition.
     23 #if defined(__GNUC__)
     24 #define MOJO_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
     25 #else
     26 #define MOJO_WARN_UNUSED_RESULT
     27 #endif
     28 
     29 #ifdef __cplusplus
     30 // Used to explicitly mark the return value of a function as unused. If you are
     31 // really sure you don't want to do anything with the return value of a function
     32 // that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
     33 //
     34 //   scoped_ptr<MyType> my_var = ...;
     35 //   if (TakeOwnership(my_var.get()) == SUCCESS)
     36 //     mojo_ignore_result(my_var.release());
     37 //
     38 template <typename T>
     39 inline void mojo_ignore_result(const T&) {
     40 }
     41 #endif
     42 
     43 // Assert things at compile time. (|msg| should be a valid identifier name.)
     44 // This macro is currently C++-only, but we want to use it in the C core.h.
     45 // Use like:
     46 //   MOJO_COMPILE_ASSERT(sizeof(Foo) == 12, Foo_has_invalid_size);
     47 #if __cplusplus >= 201103L
     48 #define MOJO_COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
     49 #elif defined(__cplusplus)
     50 namespace mojo {
     51 template <bool>
     52 struct CompileAssert {};
     53 }
     54 #define MOJO_COMPILE_ASSERT(expr, msg) \
     55   typedef ::mojo::CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1]
     56 #else
     57 #define MOJO_COMPILE_ASSERT(expr, msg)
     58 #endif
     59 
     60 // Like the C++11 |alignof| operator.
     61 #if __cplusplus >= 201103L
     62 #define MOJO_ALIGNOF(type) alignof(type)
     63 #elif defined(__GNUC__)
     64 #define MOJO_ALIGNOF(type) __alignof__(type)
     65 #elif defined(_MSC_VER)
     66 // The use of |sizeof| is to work around a bug in MSVC 2010 (see
     67 // http://goo.gl/isH0C; supposedly fixed since then).
     68 #define MOJO_ALIGNOF(type) (sizeof(type) - sizeof(type) + __alignof(type))
     69 #else
     70 #error "Please define MOJO_ALIGNOF() for your compiler."
     71 #endif
     72 
     73 // Specify the alignment of a |struct|, etc.
     74 // Use like:
     75 //   struct MOJO_ALIGNAS(8) Foo { ... };
     76 // Unlike the C++11 |alignas()|, |alignment| must be an integer. It may not be a
     77 // type, nor can it be an expression like |MOJO_ALIGNOF(type)| (due to the
     78 // non-C++11 MSVS version).
     79 #if __cplusplus >= 201103L
     80 #define MOJO_ALIGNAS(alignment) alignas(alignment)
     81 #elif defined(__GNUC__)
     82 #define MOJO_ALIGNAS(alignment) __attribute__((aligned(alignment)))
     83 #elif defined(_MSC_VER)
     84 #define MOJO_ALIGNAS(alignment) __declspec(align(alignment))
     85 #else
     86 #error "Please define MOJO_ALIGNAS() for your compiler."
     87 #endif
     88 
     89 #endif  // MOJO_PUBLIC_C_SYSTEM_MACROS_H_
     90