gecko-dev/mfbt/DebugOnly.h

78 строки
2.0 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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_
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.
*/
template<typename T>
class DebugOnly
{
public:
#ifdef DEBUG
T value;
DebugOnly() { }
DebugOnly(const T& other) : value(other) { }
DebugOnly(const DebugOnly& other) : value(other.value) { }
DebugOnly& operator=(const T& rhs) {
value = rhs;
return *this;
}
void operator++(int) {
value++;
}
void operator--(int) {
value--;
}
T* operator&() { return &value; }
operator T&() { return value; }
operator const T&() const { return value; }
T& operator->() { return value; }
#else
DebugOnly() { }
DebugOnly(const T&) { }
DebugOnly(const DebugOnly&) { }
DebugOnly& operator=(const T&) { return *this; }
void operator++(int) { }
void operator--(int) { }
#endif
/*
* DebugOnly must always have a destructor or else it will
* generate "unused variable" warnings, exactly what it's intended
* to avoid!
*/
~DebugOnly() {}
};
}
#endif /* mozilla_DebugOnly_h_ */