Use a simpler arraysize() implementation.

This commit is contained in:
John Maguire 2016-01-14 16:14:13 +00:00
parent f103bedf5b
commit ac660dcf3d
1 changed files with 5 additions and 34 deletions

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@ -1,34 +1,5 @@
// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// From Chromium src/base/macros.h
#include <stddef.h> // For size_t.
// The 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. If you use arraysize on
// a pointer by mistake, you will get a compile-time error.
//
// One caveat is that arraysize() doesn't accept any array of an
// anonymous type or a type defined inside a function. In these rare
// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is
// due to a limitation in C++'s template system. The limitation might
// eventually be removed, but it hasn't happened yet.
// This template function declaration is used in defining arraysize.
// Note that the function doesn't need an implementation, as we only
// use its type.
template <typename T, size_t N>
char (&ArraySizeHelper(T (&array)[N]))[N];
// That gcc wants both of these prototypes seems mysterious. VC, for
// its part, can't decide which to use (another mystery). Matching of
// template overloads: the final frontier.
#ifndef _MSC_VER
template <typename T, size_t N>
char (&ArraySizeHelper(const T (&array)[N]))[N];
#endif
#define arraysize(array) (sizeof(ArraySizeHelper(array)))
template <typename T>
constexpr size_t arraysize(const T&) {
static_assert(std::is_array<T>::value, "Argument must be array");
return std::extent<T>::value;
}