<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 11, 2017, at 2:02 PM, Howard Lovatt via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div 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-stroke-width: 0px;" class=""><div class="">Another possibility, other than generics, would be to drop rethrows all together and have the compiler infer if a throw is possible or not, including:</div></div><div 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-stroke-width: 0px;" class=""><br class=""></div><div 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-stroke-width: 0px;" class=""><div class="gmail_msg"> struct FStore {</div><div class="gmail_msg"> let f: () throws -> Void</div><div class="gmail_msg"> func call() throws { try f() }</div><div class="gmail_msg"> }</div></div><div class="gmail_msg" 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-stroke-width: 0px;"><br class=""></div><div class="gmail_msg" 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-stroke-width: 0px;">The compiler can make two versions, one if f can throw and one if it definitely doesn't. </div></div></blockquote><div><br class=""></div>It seems that this approach is impractical, because you either have to compile two versions of every function, or make all function bodies available for inlining, which is a non-starter for a stable ABI.</div><div><br class=""></div><div>Slava</div><div><br class=""><blockquote type="cite" class=""><div class=""><div class="gmail_msg" 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-stroke-width: 0px;"><br class=""></div><div class="gmail_msg" 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-stroke-width: 0px;">Just a thought. </div><div 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-stroke-width: 0px;" class=""><br class=""><div class="gmail_quote"><div class="">On Tue, 10 Jan 2017 at 4:29 pm, Jacob Bandes-Storch <<a href="mailto:jtbandes@gmail.com" class="">jtbandes@gmail.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div class="gmail_msg">Moving to swift-users list.<div class="gmail_extra gmail_msg"><br clear="all" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg m_3804435008049710637m_9079363423569745951gmail_signature" data-smartmail="gmail_signature"><div class="gmail_msg"><div class="gmail_msg">No, there's no way to do this today. The point of rethrows is that within one call site, "f(block)" can be treated as throwing if the block throws, or not throwing if the block doesn't throw. In your example, once the FStore object is constructed, the information about the original passed-in function is lost, so the caller has no way to know whether call() can throw or not.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">If this *were* possible, the information would somehow need to be encoded in the type system when creating FStore(f: block). That would require something like dependent typing, or generic-param-based-rethrows, e.g.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">struct FStore<T: () throws -> Void> { // made-up syntax</div><div class="gmail_msg"> <span class="Apple-converted-space"> </span>let f: T</div><div class="gmail_msg"> <span class="Apple-converted-space"> </span>func call() rethrows(T) { try f() } // throws-ness of this function depends on throws-ness of T</div><div class="gmail_msg">}</div></div></div></div><br class=""><br class=""><br class="gmail_msg"><div class="gmail_quote gmail_msg"></div></div></div><div class="gmail_msg"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg">On Mon, Jan 9, 2017 at 9:21 PM, Howard Lovatt via swift-evolution<span class="Apple-converted-space"> </span><span class="gmail_msg"><<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>></span><span class="Apple-converted-space"> </span>wrote:<br class="gmail_msg"></div></div></div><div class="gmail_msg"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div class="gmail_msg">Hi,<div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">If I have an escaping function that I store and then call, I need to declare the calling function as throwing, not rethrowing. EG:</div><div class="gmail_msg"><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><br class=""><p class="gmail_msg m_3804435008049710637m_9079363423569745951m_-6115875790740195702gmail-p1"><span class="gmail_msg m_3804435008049710637m_9079363423569745951m_-6115875790740195702gmail-s1"> </span>struct FStore {<br class="gmail_msg"> <span class="Apple-converted-space"> </span>let f: () throws -> Void<br class="gmail_msg"> <span class="Apple-converted-space"> </span>init(f: @escaping () throws -> Void) { self.f = f }<br class="gmail_msg"> <span class="Apple-converted-space"> </span>func call() throws { try f() } // Can't put rethrows here - have to use throws<br class="gmail_msg"> <span class="Apple-converted-space"> </span>}</p></div><div class="gmail_msg">Is there a better solution?</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">Thanks for any suggestions,</div><div class="gmail_msg"><br clear="all" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg m_3804435008049710637m_9079363423569745951m_-6115875790740195702gmail_signature"> <span class="Apple-converted-space"> </span>-- Howard.<br class="gmail_msg"></div></div><br class=""><br class=""></div></div><br class=""><br class=""><br class="gmail_msg"></blockquote></div></div></div><div class="gmail_msg"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin: 0px 0px 0px 0.8ex; 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