In case it turns out not to be possible to reduce the number of concepts (besides eliminating std::function), maybe it would help to change the names and behaviors of these classes to match better. Function, SharedFunction and ScopedFunction would have a much more obvious relationship to each other than Function, SharedTask and ScopedLambda.
(I'm not sure if the direct assignment from a lambda is an incidental difference or one that's required by the different ownership semantics.) - Maciej > On Jun 13, 2017, at 9:34 AM, Filip Pizlo <fpi...@apple.com> wrote: > > We should have a better story here. Right now the story is too complicated. > We have: > > - ScopedLambda or ScopedLambdaRef if you have a stack-allocated function that > outlives its user > - SharedTask if you have a heap-allocated function that you want to share and > ref-count > - WTF::Function if you have a heap-allocated function that you want to > transfer ownership (move yes, copy no) > - std::function if you have a heap-alloated function that you want to pass by > copy > > Only std::function and WTF::Function do the magic that lets you say: > > std::function f = <lambda> > > Also, std::function has the benefit that it does copying. None of the others > do that. > > ScopedLambda serves a specific purpose: it avoids allocation. Probably we > want to keep that one even if we merge the others. > > IMO SharedTask has the nicest semantics. I don’t ever want the activation of > the function to be copied. In my experience I always want sharing if more > than one reference to the function exists. I think that what we really want > in most places is a WTF::Function that has sharing semantics like SharedTask. > That would let us get rid of std::function and SharedTask. > > In the current status quo, it’s not always correct to convert std::function > to the others because: > > - Unlike ScopedLambda and SharedTask, std::function has the magic constructor > that allows you to just assign a lambda to it. > - Unlike ScopedLambda, std::function is safe if the use is not scoped. > - Unlike WTF::Function, std::function can be copied. > > -Filip > > >> On Jun 13, 2017, at 9:24 AM, Darin Adler <da...@apple.com> wrote: >> >> I’ve noticed many patches switching us from std::function to WTF::Function >> recently, to fix problems with copying and thread safety. >> >> Does std::function have any advantages over WTF::Function? Should we ever >> prefer std::function, or should we use WTF::Function everywhere in WebKit >> where we would otherwise use std::function? >> >> — Darin >> _______________________________________________ >> webkit-dev mailing list >> webkit-dev@lists.webkit.org >> https://lists.webkit.org/mailman/listinfo/webkit-dev > > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
