<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">If you replace “conjunction” by “O(n) search with early-exit on failure” and “disjunction” by just “O(n) search”, you’ll see why this can lead to computationally painful systems of constraints. &nbsp;Each disjunctive constraint may further contain or create disjunctions ad nauseum, each time incrementing the exponent in the worst-case time it takes to solve the system. &nbsp;Introduction of disjunction into an already complex system (say, one that supports constrained parametric polymorphism and subtyping AND disjunctions through overloads) makes an already difficult problem even harder.<div><br><div id="AppleMailSignature">~Robert Widmann&nbsp;</div><div><br>2018/01/13 4:45、Daryle Walker via swift-evolution &lt;<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>&gt;のメール:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><div class="">From &lt;<a href="https://github.com/apple/swift-evolution/blob/master/commonly_proposed.md#miscellaneous" class="">https://github.com/apple/swift-evolution/blob/master/commonly_proposed.md#miscellaneous</a>&gt;.</div><div class=""><br class=""></div><div class="">Maybe I’m not up on my Type Theory, but why should type constraint disjunctions be banned?</div><br class=""><div class="">
<div style="color: rgb(0, 0, 0); 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; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">—&nbsp;</div><div class="">Daryle Walker<br class="">Mac, Internet, and Video Game Junkie<br class="">darylew AT mac DOT com&nbsp;</div></div>
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