src/google/protobuf/stubs/macros.h

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
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//
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// notice, this list of conditions and the following disclaimer.
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// distribution.
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// contributors may be used to endorse or promote products derived from
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#ifndef GOOGLE_PROTOBUF_MACROS_H__
#define GOOGLE_PROTOBUF_MACROS_H__

#include <google/protobuf/stubs/port.h>

namespace google {
namespace protobuf {

#undef GOOGLE_DISALLOW_EVIL_CONSTRUCTORS
#define GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(TypeName)    \
  TypeName(const TypeName&);                           \
  void operator=(const TypeName&)

#undef GOOGLE_DISALLOW_IMPLICIT_CONSTRUCTORS
#define GOOGLE_DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
  TypeName();                                           \
  TypeName(const TypeName&);                            \
  void operator=(const TypeName&)

// ===================================================================
// from google3/base/basictypes.h

// The GOOGLE_ARRAYSIZE(arr) macro returns the # of elements in an array arr.
// The expression is a compile-time constant, and therefore can be
// used in defining new arrays, for example.
//
// GOOGLE_ARRAYSIZE catches a few type errors.  If you see a compiler error
//
//   "warning: division by zero in ..."
//
// when using GOOGLE_ARRAYSIZE, you are (wrongfully) giving it a pointer.
// You should only use GOOGLE_ARRAYSIZE on statically allocated arrays.
//
// The following comments are on the implementation details, and can
// be ignored by the users.
//
// ARRAYSIZE(arr) works by inspecting sizeof(arr) (the # of bytes in
// the array) and sizeof(*(arr)) (the # of bytes in one array
// element).  If the former is divisible by the latter, perhaps arr is
// indeed an array, in which case the division result is the # of
// elements in the array.  Otherwise, arr cannot possibly be an array,
// and we generate a compiler error to prevent the code from
// compiling.
//
// Since the size of bool is implementation-defined, we need to cast
// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
// result has type size_t.
//
// This macro is not perfect as it wrongfully accepts certain
// pointers, namely where the pointer size is divisible by the pointee
// size.  Since all our code has to go through a 32-bit compiler,
// where a pointer is 4 bytes, this means all pointers to a type whose
// size is 3 or greater than 4 will be (righteously) rejected.
//
// Kudos to Jorg Brown for this simple and elegant implementation.

#undef GOOGLE_ARRAYSIZE
#define GOOGLE_ARRAYSIZE(a) \
  ((sizeof(a) / sizeof(*(a))) / \
   static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))

// The COMPILE_ASSERT macro can be used to verify that a compile time
// expression is true. For example, you could use it to verify the
// size of a static array:
//
//   COMPILE_ASSERT(ARRAYSIZE(content_type_names) == CONTENT_NUM_TYPES,
//                  content_type_names_incorrect_size);
//
// or to make sure a struct is smaller than a certain size:
//
//   COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large);
//
// The second argument to the macro is the name of the variable. If
// the expression is false, most compilers will issue a warning/error
// containing the name of the variable.

namespace internal {

template <bool>
struct CompileAssert {
};

}  // namespace internal

#undef GOOGLE_COMPILE_ASSERT
#if __cplusplus >= 201103L
#define GOOGLE_COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
#else
#define GOOGLE_COMPILE_ASSERT(expr, msg) \
  ::google::protobuf::internal::CompileAssert<(bool(expr))> \
          msg[bool(expr) ? 1 : -1]; \
  (void)msg
// Implementation details of COMPILE_ASSERT:
//
// - COMPILE_ASSERT works by defining an array type that has -1
//   elements (and thus is invalid) when the expression is false.
//
// - The simpler definition
//
//     #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1]
//
//   does not work, as gcc supports variable-length arrays whose sizes
//   are determined at run-time (this is gcc's extension and not part
//   of the C++ standard).  As a result, gcc fails to reject the
//   following code with the simple definition:
//
//     int foo;
//     COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is
//                               // not a compile-time constant.
//
// - By using the type CompileAssert<(bool(expr))>, we ensures that
//   expr is a compile-time constant.  (Template arguments must be
//   determined at compile-time.)
//
// - The outter parentheses in CompileAssert<(bool(expr))> are necessary
//   to work around a bug in gcc 3.4.4 and 4.0.1.  If we had written
//
//     CompileAssert<bool(expr)>
//
//   instead, these compilers will refuse to compile
//
//     COMPILE_ASSERT(5 > 0, some_message);
//
//   (They seem to think the ">" in "5 > 0" marks the end of the
//   template argument list.)
//
// - The array size is (bool(expr) ? 1 : -1), instead of simply
//
//     ((expr) ? 1 : -1).
//
//   This is to avoid running into a bug in MS VC 7.1, which
//   causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1.
#endif  // __cplusplus >= 201103L

}  // namespace protobuf
}  // namespace google

#endif  // GOOGLE_PROTOBUF_MACROS_H__