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/* -*- 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
#ifndef nsISupportsUtils_h__
#define nsISupportsUtils_h__
#include <type_traits>
#include "nscore.h"
#include "nsIOutputStream.h"
#include "nsISupports.h"
#include "nsError.h"
#include "nsDebug.h"
#include "nsISupportsImpl.h"
#include "mozilla/RefPtr.h"
/**
* Macro for adding a reference to an interface.
* @param _ptr The interface pointer.
*/
#define NS_ADDREF(_ptr) (_ptr)->AddRef()
/**
* Macro for adding a reference to this. This macro should be used
* because NS_ADDREF (when tracing) may require an ambiguous cast
* from the pointers primary type to nsISupports. This macro sidesteps
* that entire problem.
*/
#define NS_ADDREF_THIS() AddRef()
// Making this a |inline| |template| allows |aExpr| to be evaluated only once,
// yet still denies you the ability to |AddRef()| an |nsCOMPtr|.
template <class T>
inline void ns_if_addref(T aExpr) {
if (aExpr) {
aExpr->AddRef();
}
}
/**
* Macro for adding a reference to an interface that checks for nullptr.
* @param _expr The interface pointer.
*/
#define NS_IF_ADDREF(_expr) ns_if_addref(_expr)
/*
* Given these declarations, it explicitly OK and efficient to end a `getter'
* with:
*
* NS_IF_ADDREF(*result = mThing);
*
* even if |mThing| is an |nsCOMPtr|. If |mThing| is an |nsCOMPtr|, however, it
* is still _illegal_ to say |NS_IF_ADDREF(mThing)|.
*/
/**
* Macro for releasing a reference to an interface.
* @param _ptr The interface pointer.
*/
#define NS_RELEASE(_ptr) \
do { \
(_ptr)->Release(); \
(_ptr) = 0; \
} while (0)
/**
* Macro for releasing a reference to this interface.
*/
#define NS_RELEASE_THIS() Release()
/**
* Macro for releasing a reference to an interface, except that this
* macro preserves the return value from the underlying Release call.
* The interface pointer argument will only be NULLed if the reference count
* goes to zero.
*
* @param _ptr The interface pointer.
* @param _rc The reference count.
*/
#define NS_RELEASE2(_ptr, _rc) \
do { \
_rc = (_ptr)->Release(); \
if (0 == (_rc)) (_ptr) = 0; \
} while (0)
/**
* Macro for releasing a reference to an interface that checks for nullptr;
* @param _ptr The interface pointer.
*/
#define NS_IF_RELEASE(_ptr) \
do { \
if (_ptr) { \
(_ptr)->Release(); \
(_ptr) = 0; \
} \
} while (0)
/*
* Often you have to cast an implementation pointer, e.g., |this|, to an
* |nsISupports*|, but because you have multiple inheritance, a simple cast
* is ambiguous. One could simply say, e.g., (given a base |nsIBase|),
* |static_cast<nsIBase*>(this)|; but that disguises the fact that what
* you are really doing is disambiguating the |nsISupports|. You could make
* that more obvious with a double cast, e.g., |static_cast<nsISupports*>
(*
static_cast<nsIBase*>(this))|, but that is bulky and harder to read...
*
* The following macro is clean, short, and obvious. In the example above,
* you would use it like this: |NS_ISUPPORTS_CAST(nsIBase*, this)|.
*/
#define NS_ISUPPORTS_CAST(__unambiguousBase, __expr) \
static_cast<nsISupports*>(static_cast<__unambiguousBase>(__expr))
// a type-safe shortcut for calling the |QueryInterface()| member function
template <class T, class DestinationType>
inline nsresult CallQueryInterface(T* aSource, DestinationType** aDestination) {
// We permit nsISupports-to-nsISupports here so that one can still obtain
// the canonical nsISupports pointer with CallQueryInterface.
static_assert(
!(std::is_same_v<DestinationType, T> ||
std::is_base_of<DestinationType, T>::value) ||
std::is_same_v<DestinationType, nsISupports>,
"don't use CallQueryInterface for compile-time-determinable casts");
MOZ_ASSERT(aSource, "null parameter");
MOZ_ASSERT(aDestination, "null parameter");
return aSource->QueryInterface(NS_GET_TEMPLATE_IID(DestinationType),
reinterpret_cast<void**>(aDestination));
}
template <class SourceType, class DestinationType>
inline nsresult CallQueryInterface(RefPtr<SourceType>& aSourcePtr,
DestinationType** aDestPtr) {
return CallQueryInterface(aSourcePtr.get(), aDestPtr);
}
#endif /* __nsISupportsUtils_h */