gecko/mfbt/Util.h

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sw=4 et tw=99 ft=cpp:
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at:
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Code.
*
* The Initial Developer of the Original Code is
* The Mozilla Foundation
* Portions created by the Initial Developer are Copyrigght (C) 2011
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef mozilla_Util_h_
#define mozilla_Util_h_
#ifdef __cplusplus
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 along with ASSERT()-style macros, allowing one
* to write
*
* DebugOnly<bool> check = Func();
* 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.
*/
template <typename T>
struct DebugOnly
{
#ifdef DEBUG
T value;
DebugOnly() {}
DebugOnly(const T& other) : value(other) {}
DebugOnly& operator=(const T& rhs) {
value = rhs;
return *this;
}
operator T&() { return value; }
operator const T&() const { return value; }
#else
DebugOnly() {}
DebugOnly(const T&) {}
DebugOnly& operator=(const T&) {}
#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 /* __cplusplus */
#endif /* mozilla_Util_h_ */