<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></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 29, 2016, at 3:03 PM, Dave Abrahams 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=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">on Fri Jan 29 2016, Alex Migicovsky <</span><a href="mailto:swift-evolution@swift.org" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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="">swift-evolution@swift.org</a><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">> wrote:</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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 style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><blockquote type="cite" class="">On Jan 29, 2016, at 8:33 AM, Dave Abrahams via swift-evolution<br class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""><br class="">on Thu Jan 28 2016, Alex Migicovsky<br class=""></blockquote><br class=""><blockquote type="cite" class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><<a href="mailto:swift-evolution@swift.org" class="">mailto:swift-evolution@swift.org</a>>><br class="">wrote:<br class=""><br class=""><blockquote type="cite" class=""><blockquote type="cite" class="">On Jan 27, 2016, at 3:33 PM, Jordan Rose via swift-evolution<br class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""><blockquote type="cite" class=""><br class="">On Jan 26, 2016, at 18:06, Dany St-Amant via swift-evolution<br class=""></blockquote></blockquote><br class=""><blockquote type="cite" class=""><blockquote type="cite" class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""><br class=""><blockquote type="cite" class="">Le 26 janv. 2016 à 19:39, Dave Abrahams via swift-evolution<br class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit<br class="">:<br class=""><br class=""><br class="">on Tue Jan 26 2016, Charles Kissinger <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""><blockquote type="cite" class="">I agree with all of the small criticisms mentioned below by Radoslaw<br class="">except for the renaming of precondition() to require(). I think it is<br class="">an improvement that it describes an action now, just like assert().<br class=""></blockquote><br class="">Interestingly, I was the one that insisted on that change, as I felt<br class="">“precondition” was too much of a term-of-art and “require” would be more<br class="">accessible, but I am now regretting that decision. This function is not<br class="">conceptually an action; like “assert,” it's a declarative statement, and<br class="">“precondition” conveyed that aspect much better, IMO.<br class=""></blockquote><br class="">How about expect()? Should not have much string attached to it. Only thing coming to mind is the<span class="Apple-converted-space"> </span><br class="">TCL extension used for automation.<br class=""></blockquote><br class="">That's not bad, but to me "expect" seems more open-ended than<br class="">"require" or "precondition", i.e. "if it isn't true, then what?". I<br class="">don't assume that it's going to be fatal.<br class=""><br class="">(It even feels a little like an optimization hint to me, like<br class="">"expect(self.dynamicType === BaseClass.self)". It could still be a<br class="">subclass, but the compiler would know what the common case is.)<br class=""></blockquote><br class="">Someone I spoke with had a good idea about this IMO. They recommended<br class="">we have debugAssert and releaseAssert (or debugRequire and<br class="">releaseRequire). I think this makes the semantics obvious and has<br class="">consistent terminology between the functions. There’s no question at<br class="">the call site what was intended.<br class=""></blockquote><br class="">Here's the problem with that suggestion: these things really have<br class="">completely different purposes; we don't want them to lose the semantic<br class="">distinction that "this is a sanity check (assert)" and "this is checking<br class="">whether my client is breaking his contract (precondition).” <br class=""></blockquote><br class="">I think that naming convention works fine as long as you think about<br class="">the behavior as tied to how the module that contains that code is<br class="">compiled, right? If you use debugAssert in a module that compiles as<br class="">debug, then that assert will be checked. If you use releaseAssert, it<br class="">will be checked in both release and debug. Maybe I’m missing something<br class="">here though...<br class=""><br class="">One thing I’d really like to improve about the current naming is<br class="">making it obvious at the call site what the behavior of the function<br class="">is. I find that with the current names it’s just a memorization<br class="">game—and I’m not good at memorization :-)<br class=""></blockquote><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">You're not supposed to think about the behavior when you use it. You're</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">supposed to ask, "am I checking to make sure that I haven't messed up</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">(e.g. broken invariants), or that my client hasn't messed up</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">(precondition violation)?”</span></div></blockquote><div><br class=""></div><div>If that’s really the intended axis `precondition` is better than `require` or similar.</div><div><br class=""></div><div>Another outlook on asserts is essentially that you should classify each potential assertion on two axes:</div><div><br class=""></div><div>- semantic importance of checked invariant (e.g. “expected” vs “requirement”)</div><div>- performance impact of check (e.g. negligible, moderate overhead, or materially-slower (e.g. O(n) -> O(n^2))</div><div><br class=""></div><div>…and then use a suitably-“strong” strength-of-assertion for that setting.</div><div><br class=""></div><div>I think at least a few of us have been interpreting the two assertion types along these lines—in spite of the name!—whence the focus on the “what is included in which build types?” behavior.</div><br class=""><blockquote type="cite" class=""><div class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">--<span class="Apple-converted-space"> </span></span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">-Dave</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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 style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; 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