<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div><blockquote type="cite" class=""><div class="">On Mar 29, 2018, at 2:47 PM, John McCall via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" class="">cfe-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="" class=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">On Mar 29, 2018, at 2:31 PM, David Chisnall <<a href="mailto:David.Chisnall@cl.cam.ac.uk" class="">David.Chisnall@cl.cam.ac.uk</a>> wrote:<br class="">On 29 Mar 2018, at 19:22, John McCall <<a href="mailto:rjmccall@apple.com" class="">rjmccall@apple.com</a>> wrote:<br class=""><blockquote type="cite" class=""><br class=""><blockquote type="cite" class="">On a related note, I’ve been considering whether it’s possible to provide helpers to improve NSInvocation’s handling of Objective-C++ messages that take types with either nontrivial copy constructors or no copy constructor.<br class=""><br class="">My motivation for this was writing some code using higher-order messaging to perform things in another thread, which worked fine until I passed it a std::shared_ptr, at which point NSInvocation did a simple memcpy of the argument frame and I was left with a dangling pointer. I eventually rewrote this code to use lambdas, but it would be nice if an NSInvocation constructed from a message containing a std::shared_ptr argument actually did the reference count manipulations correctly when copying the argument from the stack / registers into the NSInvocation object. Most methods have trivially copyable arguments / return values (except for Objective-C objects, which NSInvocation can already handle automatically), so the metadata would only have to be for the (hopefully, relatively small) subset of C++ types that are not trivially copyable and are passed as Objective-C method arguments. Do you have any thoughts?<br class=""></blockquote><br class="">Honestly? I think NSInvocation ought to be deprecated in favor of just using blocks or, if blocks are unacceptable, static code-generation techniques. NSInvocation works well enough for a highly reduced set of function prototypes, but the idea that it's going to transparently support every possible thing that the compiler knows how to do in a call seems pretty fanciful to me.<br class=""></blockquote><br class="">Unfortunately, using blocks means that you can’t use any of the higher-order messaging patterns, which makes the code a lot more verbose and a lot less composable. If C++ compile-time reflection lands then I suppose most use cases could be handled with that, as long as we provide ObjC++ extensions to allow the reflection to work in the same way.<br class=""></blockquote><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Well, but does that mean that blocks aren't the right answer, or does it mean that you should be generating your blocks with code-generation techniques like macros or templates?</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""></div></div></blockquote><div><br class=""></div></div>For example, to combine a couple streams here:<div class=""><br class=""></div><div class="">If you could write @selector(-NSWidget.foo:bar:), and that you gave you a SEL<void(NSWidget*, float, std::unique_ptr<Gadget> &&)>, it would be relatively straightforward to write a variadic template function that took that selector and the corresponding arguments and a dispatch queue and called dispatch_after with a block which captured all the arguments by-value and in its body did a message of that selector which forwarded all the captured arguments.</div><div class=""><br class=""></div><div class="">John.</div></body></html>