mfbt/DebugOnly.h
author B2G Bumper Bot <release+b2gbumper@mozilla.com>
Mon, 22 Feb 2016 20:52:33 -0800
changeset 325574 f177f8ec083efc5ddb5d3c854ae7bb383b1b6a45
parent 301853 4d203aca24e3a471ab627fd5d919612ea9ab0e35
child 321235 5f729d20fd00033855fd99575eda4d60bc172c4a
permissions -rw-r--r--
Bumping gaia.json for 2 gaia revision(s) a=gaia-bump ======== https://hg.mozilla.org/integration/gaia-central/rev/8c0f20540765 Author: Ricky Chien <rickychien@users.noreply.github.com> Desc: Merge pull request #34079 from rickychien/show-hint-after-load Bug 1250032 - [Marketplace] Hint should show after the app finish loading r=@luke-chang ======== https://hg.mozilla.org/integration/gaia-central/rev/8dd0b87892a1 Author: Ricky Chien <ricky060709@gmail.com> Desc: Bug 1250032 - [Marketplace] Hint should show after the app finish loading

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
 * Provides DebugOnly, a type for variables used only in debug builds (i.e. by
 * assertions).
 */

#ifndef mozilla_DebugOnly_h
#define mozilla_DebugOnly_h

#include "mozilla/Attributes.h"

namespace mozilla {

/**
 * DebugOnly contains a value of type T, but only in debug builds.  In release
 * builds, it does not contain a value.  This helper is intended to be used with
 * MOZ_ASSERT()-style macros, allowing one to write:
 *
 *   DebugOnly<bool> check = func();
 *   MOZ_ASSERT(check);
 *
 * more concisely than declaring |check| conditional on #ifdef DEBUG, but also
 * without allocating storage space for |check| in release builds.
 *
 * DebugOnly instances can only be coerced to T in debug builds.  In release
 * builds they don't have a value, so type coercion is not well defined.
 *
 * Note that DebugOnly instances still take up one byte of space, plus padding,
 * when used as members of structs.
 */
template<typename T>
class DebugOnly
{
public:
#ifdef DEBUG
  T value;

  DebugOnly() { }
  MOZ_IMPLICIT DebugOnly(const T& aOther) : value(aOther) { }
  DebugOnly(const DebugOnly& aOther) : value(aOther.value) { }
  DebugOnly& operator=(const T& aRhs) {
    value = aRhs;
    return *this;
  }

  void operator++(int) { value++; }
  void operator--(int) { value--; }

  // Do not define operator+=(), etc. here.  These will coerce via the
  // implicit cast and built-in operators.  Defining explicit methods here
  // will create ambiguity the compiler can't deal with.

  T* operator&() { return &value; }

  operator T&() { return value; }
  operator const T&() const { return value; }

  T& operator->() { return value; }
  const T& operator->() const { return value; }

#else
  DebugOnly() { }
  MOZ_IMPLICIT DebugOnly(const T&) { }
  DebugOnly(const DebugOnly&) { }
  DebugOnly& operator=(const T&) { return *this; }
  void operator++(int) { }
  void operator--(int) { }
  DebugOnly& operator+=(const T&) { return *this; }
  DebugOnly& operator-=(const T&) { return *this; }
  DebugOnly& operator&=(const T&) { return *this; }
  DebugOnly& operator|=(const T&) { return *this; }
  DebugOnly& operator^=(const T&) { return *this; }
#endif

  /*
   * DebugOnly must always have a destructor or else it will
   * generate "unused variable" warnings, exactly what it's intended
   * to avoid!
   */
  ~DebugOnly() {}
};

} // namespace mozilla

#endif /* mozilla_DebugOnly_h */