gecko-dev/dom/base/nsDOMScriptObjectHolder.h

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/* -*- 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/. */
#ifndef nsDOMScriptObjectHolder_h__
#define nsDOMScriptObjectHolder_h__
#include "nsIScriptContext.h"
#include "nsIDOMScriptObjectFactory.h"
#include "jspubtd.h"
// A thin class used to help with script object memory management. No virtual
// functions and a fully inline implementation should keep the cost down.
// [Note that a fully inline implementation is necessary for use by other
// languages, which do not link against the layout component module]
template<class T>
class NS_STACK_CLASS nsScriptObjectHolder {
public:
// A constructor that will cause a reference to |ctx| to be stored in
// the object. Only use for short-lived object holders.
nsScriptObjectHolder<T>(nsIScriptContext *ctx, T* aObject = nullptr) :
mObject(aObject), mContext(ctx) {
NS_ASSERTION(ctx, "Must provide a valid context");
}
// copy constructor
nsScriptObjectHolder<T>(const nsScriptObjectHolder<T>& other) :
mObject(other.mObject),
mContext(other.mContext)
{
// New hold the script object and new reference on the script context.
if (mObject)
mContext->HoldScriptObject(mObject);
}
~nsScriptObjectHolder<T>() {
if (mObject)
mContext->DropScriptObject(mObject);
}
// misc operators
nsScriptObjectHolder<T> &operator=(const nsScriptObjectHolder<T> &other) {
set(other);
return *this;
}
bool operator!() const {
return !mObject;
}
operator bool() const {
return !!mObject;
}
T* get() const {
return mObject;
}
// Drop the script object - but *not* the nsIScriptContext.
nsresult drop() {
nsresult rv = NS_OK;
if (mObject) {
rv = mContext->DropScriptObject(mObject);
mObject = nullptr;
}
return rv;
}
nsresult set(T* object) {
nsresult rv = drop();
if (NS_FAILED(rv))
return rv;
if (object) {
rv = mContext->HoldScriptObject(object);
// don't store the pointer if we failed to lock it.
if (NS_SUCCEEDED(rv)) {
mObject = object;
}
}
return rv;
}
nsresult set(const nsScriptObjectHolder<T> &other) {
nsresult rv = drop();
if (NS_FAILED(rv))
return rv;
return set(other.mObject);
}
protected:
T* mObject;
nsCOMPtr<nsIScriptContext> mContext;
};
#endif // nsDOMScriptObjectHolder_h__