On Fri, Apr 10, 2015 at 10:37 AM, Ehsan Akhgari <ehsan.akhg...@gmail.com> wrote:
> On 2015-04-10 12:33 PM, Andrew McCreight wrote: > >> >> >> On Fri, Apr 10, 2015 at 8:46 AM, Ehsan Akhgari <ehsan.akhg...@gmail.com >> <mailto:ehsan.akhg...@gmail.com>> wrote: >> >> I would like to propose that we should ban the usage of refcounted >> objects >> inside lambdas in Gecko. Here is the reason: >> >> Consider the following code: >> >> nsINode* myNode; >> TakeLambda([&]() { >> myNode->Foo(); >> }); >> >> >> How is this any worse than any other usage of raw pointers on the stack? >> >> nsINode* myNode; >> doSomething(); >> myNode->Foo(); >> >> is the same thing. >> > > It is worse since the lambda may be held on to and executed later in the > future (i.e., past the point in time when the function returns.) > > But also do note that raw pointers to refcounted objects on the stack are > very dangerous as well (for example in your above code, doSomething() could > destroy myNode. > > I also don't see how "don't use any refcounted objects inside lambdas" >> is any easier to enforce. >> > > It's easier because we don't yet have piles of code which have this > pattern in them. I would like to prevent us getting there so that we don't > have to start solving this issue on a massive scale in a few years once we > grow more lambda usage. > > I also don't see why refcounted objects in particular are worth of >> exclusion based on their lifetime in closures, but not references to >> other allocated things. I guess we don't have local variables like >> |nsTArray<Foo>* myArray;| as often, but that would be just as dangerous. >> > > Yes, I have nothing against coming up with further restrictions to make > more things safe, but mentioning other dangerous things is not an argument > against this proposal. ;-) > Well, I don't really see what is difficult about this in particular, but I've been writing code in functional programming languages for a long time, so maybe I'm just used to the lifetime issues around closures already. _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
