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<!DOCTYPE html> <html xmlns='http://www.w3.org/1999/xhtml' xmlns:b='http://www.google.com/2005/gml/b' xmlns:data='http://www.google.com/2005/gml/data' xmlns:expr='http://www.google.com/2005/gml/expr'> <head> <link href='https://www.blogger.com/static/v1/widgets/55013136-widget_css_bundle.css' rel='stylesheet' type='text/css'/> <meta content='text/html; charset=UTF-8' http-equiv='Content-Type'/> <meta content='blogger' name='generator'/> <link href='https://gafter.blogspot.com/favicon.ico' rel='icon' type='image/x-icon'/> <link href='http://gafter.blogspot.com/2020/' rel='canonical'/> <link rel="alternate" type="application/atom+xml" title="Neal Gafter's blog - Atom" href="https://gafter.blogspot.com/feeds/posts/default" /> <link rel="alternate" type="application/rss+xml" title="Neal Gafter's blog - RSS" href="https://gafter.blogspot.com/feeds/posts/default?alt=rss" /> <link rel="service.post" type="application/atom+xml" title="Neal Gafter's blog - Atom" href="https://www.blogger.com/feeds/7803021/posts/default" />  <meta content='http://gafter.blogspot.com/2020/' property='og:url'/> <meta content='Neal Gafter's blog' property='og:title'/> <meta content='Thoughts about Programming Languages, Science and Philosophy.' property='og:description'/> <title>Neal Gafter's blog: 2020</title> <style id='page-skin-1' type='text/css'></style> <link href='https://www.blogger.com/dyn-css/authorization.css?targetBlogID=7803021&zx=ec521dc9-f6a0-4bc7-9244-fe69ed71716a' media='none' onload='if(media!='all')media='all'' rel='stylesheet'/><noscript><link href='https://www.blogger.com/dyn-css/authorization.css?targetBlogID=7803021&zx=ec521dc9-f6a0-4bc7-9244-fe69ed71716a' rel='stylesheet'/></noscript> <meta name='google-adsense-platform-account' content='ca-host-pub-1556223355139109'/> <meta name='google-adsense-platform-domain' content='blogspot.com'/> </head> <body> <div class='navbar section' id='navbar'><div class='widget Navbar' data-version='1' id='Navbar1'><script type="text/javascript"> function setAttributeOnload(object, attribute, val) { if(window.addEventListener) { window.addEventListener('load', function(){ object[attribute] = val; 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It demonstrates that you can add declarations to the body without interfering with their useful semantics:</p><p></p><blockquote style="border: none; margin: 0px 0px 0px 40px; padding: 0px;"><pre style="background-color: white; font-family: Menlo; font-size: 9pt;"><span style="color: navy; font-weight: bold;">import </span>kotlin.math.sqrt<br /><span style="color: navy; font-weight: bold;">import </span>kotlin.collections.HashSet<br /><br /><span style="color: navy; font-weight: bold;">public data class </span>Cartesian(<span style="color: navy; font-weight: bold;">val </span><span style="color: #660e7a; font-weight: bold;">x</span>: Float, <span style="color: navy; font-weight: bold;">val </span><span style="color: #660e7a; font-weight: bold;">y</span>: Float) {<br /><br /> <span style="color: navy; font-weight: bold;">private var </span><span style="color: #660e7a; font-weight: bold;">cachedR</span>: Float = <span style="color: blue;">0F<br /></span><span style="color: blue;"> </span><span style="color: navy; font-weight: bold;">public val </span><span style="color: #660e7a; font-weight: bold;">r</span>: Float<br /> <span style="color: navy; font-weight: bold;">get</span>() {<br /> <span style="color: navy; font-weight: bold;">var </span>localR = <span style="color: #660e7a; font-weight: bold;">cachedR</span>;<br /> <span style="color: navy; font-weight: bold;">if </span>(localR == <span style="color: blue;">0F</span>) {<br /> localR = <span style="font-style: italic;">sqrt</span>(<span style="color: #660e7a; font-weight: bold;">x</span>*<span style="color: #660e7a; font-weight: bold;">x </span>+ <span style="color: #660e7a; font-weight: bold;">y</span>*<span style="color: #660e7a; font-weight: bold;">y</span>)<br /> <span style="color: #660e7a; font-weight: bold;">cachedR </span>= localR<br /> }<br /> <span style="color: navy; font-weight: bold;">return </span>localR<br /> }<br />}<br /><br /><span style="color: navy; font-weight: bold;">fun </span>main(args: Array<String>) {<br /> <span style="color: navy; font-weight: bold;">val </span>set = HashSet<Cartesian>()<br /> <span style="color: navy; font-weight: bold;">val </span>c1 = Cartesian(<span style="color: blue;">5F</span>, <span style="color: blue;">12F</span>)<br /> set.add(c1)<br /> <span style="font-style: italic;">println</span>(c1.<span style="color: #660e7a; font-weight: bold;">r</span>) <span style="color: grey; font-style: italic;">// prints 13.0<br /></span><span style="color: grey; font-style: italic;"> </span><span style="font-style: italic;">println</span>(set.contains(c1)) <span style="color: grey; font-style: italic;">// prints true<br /></span><span style="color: grey; font-style: italic;"><br /></span><span style="color: grey; font-style: italic;"> </span><span style="color: navy; font-weight: bold;">val </span>c2 = Cartesian(<span style="color: blue;">5F</span>, <span style="color: blue;">12F</span>)<br /> <span style="font-style: italic;">println</span>(set.contains(c2)) <span style="color: grey; font-style: italic;">// prints true<br /></span><span style="color: grey; font-style: italic;"><br /></span><span style="color: grey; font-style: italic;"> </span><span style="color: navy; font-weight: bold;">val </span>c3 = c1.copy(<span style="color: #4a86e8;">x = </span><span style="color: blue;">9F</span>)<br /> <span style="font-style: italic;">println</span>(c3.<span style="color: #660e7a; font-weight: bold;">r</span>) <span style="color: grey; font-style: italic;">// prints 15.0 </span>}</pre></blockquote><p></p><p>I tried records in C# 9.0, and I was disappointed by some of the behavior.  Here is an "equivalent" fragment of C#.  Can you guess what it does?</p><blockquote style="border: none; margin: 0px 0px 0px 40px; padding: 0px;"><p><span style="font-family: courier;"><span style="color: #2b00fe;">using</span> System;<br /><span style="color: #2b00fe;">using</span> System.Collections.Generic;<br /><br /><span style="color: #2b00fe;">public record</span> Cartesian(<span style="color: #2b00fe;">float</span> X, </span><span style="color: #2b00fe; font-family: courier;">float</span><span style="font-family: courier;"> Y)<br />{<br />    <span style="color: #2b00fe;">private</span> </span><span style="color: #2b00fe; font-family: courier;">float</span><span style="font-family: courier;"> cachedR = 0F;<br />    <span style="color: #2b00fe;">public</span> </span><span style="color: #2b00fe; font-family: courier;">float</span><span style="font-family: courier;"> R<br />    {<br />        <span style="color: #2b00fe;">get</span><br />        {<br />            </span><span style="color: #2b00fe; font-family: courier;">float</span><span style="font-family: courier;"> r = cachedR;<br />            <span style="color: #a64d79;">if</span> (r == 0F)<br />                r = cachedR = (</span><span style="color: #2b00fe; font-family: courier;">float</span><span style="font-family: courier;">)<span style="color: #3d85c6;">Math</span>.<span style="color: #674ea7;">Sqrt</span>(X * X + Y * Y);<br />            <span style="color: #a64d79;">return</span> r;<br />        }<br />    }<br />}<br /><br /><span style="color: #2b00fe;">class</span> <span style="color: #3d85c6;">Program</span><br />{<br />    static void <span style="color: #674ea7;">Main</span>()<br />    {<br />        <span style="color: #2b00fe;">var</span> set = new <span style="color: #3d85c6;">HashSet</span><<span style="color: #3d85c6;">Cartesian</span>>();<br />        </span><span style="color: #2b00fe; font-family: courier;">var</span><span style="font-family: courier;"> c1 = new <span style="color: #3d85c6;">Cartesian</span>(5, 12);<br />        set.<span style="color: #674ea7;">Add</span>(c1);<br />        <span style="color: #3d85c6;">Console</span>.<span style="color: #674ea7;">WriteLine</span>(c1.R);              // 1<br />        </span><span style="color: #3d85c6; font-family: courier;">Console</span><span style="font-family: courier;">.</span><span style="color: #674ea7; font-family: courier;">WriteLine</span><span style="font-family: courier;">(set.<span style="color: #674ea7;">Contains</span>(c1));  // 2<br /><br />        </span><span style="color: #2b00fe; font-family: courier;">var</span><span style="font-family: courier;"> c2 = new </span><span style="color: #3d85c6; font-family: courier;">Cartesian</span><span style="font-family: courier;">(5, 12);<br />        </span><span style="color: #3d85c6; font-family: courier;">Console</span><span style="font-family: courier;">.</span><span style="color: #674ea7; font-family: courier;">WriteLine</span><span style="font-family: courier;">(set.</span><span style="color: #674ea7; font-family: courier;">Contains</span><span style="font-family: courier;">(c2));  // 3<br /><br />        // with expression not specified<br />        </span><span style="color: #2b00fe; font-family: courier;">var</span><span style="font-family: courier;"> c3 = c1 with { X = 9 };           // 4<br />        </span><span style="color: #3d85c6; font-family: courier;">Console</span><span style="font-family: courier;">.</span><span style="color: #674ea7; font-family: courier;">WriteLine</span><span style="font-family: courier;">(c3.R);              // 5<br />    }<br />}</span></p></blockquote><p>My hope would be that it would behave approximately the same as the Kotlin program (and the same as equivalent programs in Java or Scala).  But in C# <i>all fields</i> (even private ones) are considered key members of a record.  Consequently,</p><p></p><ol style="text-align: left;"><li>(in the line marked "<span style="font-family: courier;">// 1</span>") The use of the property <span style="font-family: courier;">c1.R</span> changes the logical value of <span style="font-family: courier;">c1</span>.</li><li>Since it is not the same as the record that was added to the set, the modified record is no longer seen as a member of the set.</li><li>Since the record contained in the set has been modified (records are reference types), it is no longer seen as equals to a fresh record which has not had its <span style="font-family: courier;">R</span> property sampled.</li><li>C#'s <span style="font-family: courier;">with</span> expression produces a fresh instance with <i>all</i> of the fields copied, bypassing the constructor.</li><li>Therefore the field <span style="font-family: courier;">cachedR</span> is initialized to an incorrect value.</li></ol><p></p><p>Due to these issues, programmers would be wise to use C# records in only the simplest scenarios.</p></p> <div style='clear: both;'></div> </div> <div class='post-footer'> <p class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/7803021/3581756692255860518' onclick=''>2 comments</a> </span> <span class='post-icons'> </span> <span class='post-backlinks post-comment-link'> </span> </p> <p 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class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2008/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2008/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2007/'> 2007 </a> <span class='post-count' dir='ltr'>(18)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' 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href='https://gafter.blogspot.com/2007/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2007/01/'> January </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2006/'> 2006 </a> <span class='post-count' dir='ltr'>(20)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2006/12/'> December </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2006/11/'> November </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2006/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2006/09/'> September </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2006/08/'> August </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2005/'> 2005 </a> <span class='post-count' dir='ltr'>(2)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2005/02/'> February </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2004/'> 2004 </a> <span class='post-count' dir='ltr'>(1)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='https://gafter.blogspot.com/2004/09/'> September </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> </div> </div> <div class='clear'></div> </div> </div><div class='widget Profile' data-version='1' id='Profile1'> <h2>About Me</h2> <div class='widget-content'> <dl class='profile-datablock'> <dt class='profile-data'> <a class='profile-name-link g-profile' href='https://www.blogger.com/profile/08579466817032124881' rel='author' style='background-image: url(//www.blogger.com/img/logo-16.png);'> Neal Gafter </a> </dt> <dd class='profile-textblock'>Neal Gafter is a Computer Programming Language Designer and Implementer, Amateur Scientist and Philosopher. He works on the Rel compiler at Relational.AI. He previously worked for Microsoft on C#, for Google on Calendar, and for Sun Microsystems on Java. Neal was granted an OpenJDK Community Innovators' Challenge award for his design and implementation of lambda expressions for Java. He is coauthor of <em>Java Puzzlers: Traps, Pitfalls, and Corner Cases</em> (Addison Wesley, 2005). He was a member of the C++ Standards Committee and led the development of C and C++ compilers at Sun Microsystems, Microtec Research, and Texas Instruments. He holds a Ph.D. in computer science from the University of Rochester.</dd> </dl> <a class='profile-link' href='https://www.blogger.com/profile/08579466817032124881' rel='author'>View my complete profile</a> <div class='clear'></div> </div> </div></div> </div>  <div class='clear'> </div> </div>  <div id='footer-wrapper'> <div class='footer no-items section' id='footer'></div> </div> </div></div>  <script src="//www.google-analytics.com/urchin.js" type="text/javascript"> </script> <script type='text/javascript'> _uacct = "UA-605497-1"; urchinTracker(); </script> <script type="text/javascript" src="https://www.blogger.com/static/v1/widgets/2806328968-widgets.js"></script> <script type='text/javascript'> window['__wavt'] = 'AOuZoY61TUoLM478iLtiYqGf6Cp5sA4mhQ:1743839351856';_WidgetManager._Init('//www.blogger.com/rearrange?blogID\x3d7803021','//gafter.blogspot.com/2020/','7803021'); _WidgetManager._SetDataContext([{'name': 'blog', 'data': {'blogId': '7803021', 'title': 'Neal Gafter\x27s blog', 'url': 'https://gafter.blogspot.com/2020/', 'canonicalUrl': 'http://gafter.blogspot.com/2020/', 'homepageUrl': 'https://gafter.blogspot.com/', 'searchUrl': 'https://gafter.blogspot.com/search', 'canonicalHomepageUrl': 'http://gafter.blogspot.com/', 'blogspotFaviconUrl': 'https://gafter.blogspot.com/favicon.ico', 'bloggerUrl': 'https://www.blogger.com', 'hasCustomDomain': false, 'httpsEnabled': true, 'enabledCommentProfileImages': true, 'gPlusViewType': 'FILTERED_POSTMOD', 'adultContent': false, 'analyticsAccountNumber': '', 'encoding': 'UTF-8', 'locale': 'en', 'localeUnderscoreDelimited': 'en', 'languageDirection': 'ltr', 'isPrivate': false, 'isMobile': false, 'isMobileRequest': false, 'mobileClass': '', 'isPrivateBlog': false, 'isDynamicViewsAvailable': false, 'feedLinks': '\x3clink rel\x3d\x22alternate\x22 type\x3d\x22application/atom+xml\x22 title\x3d\x22Neal Gafter\x26#39;s blog - Atom\x22 href\x3d\x22https://gafter.blogspot.com/feeds/posts/default\x22 /\x3e\n\x3clink rel\x3d\x22alternate\x22 type\x3d\x22application/rss+xml\x22 title\x3d\x22Neal Gafter\x26#39;s blog - RSS\x22 href\x3d\x22https://gafter.blogspot.com/feeds/posts/default?alt\x3drss\x22 /\x3e\n\x3clink rel\x3d\x22service.post\x22 type\x3d\x22application/atom+xml\x22 title\x3d\x22Neal Gafter\x26#39;s blog - Atom\x22 href\x3d\x22https://www.blogger.com/feeds/7803021/posts/default\x22 /\x3e\n', 'meTag': '', 'adsenseHostId': 'ca-host-pub-1556223355139109', 'adsenseHasAds': false, 'adsenseAutoAds': false, 'boqCommentIframeForm': true, 'loginRedirectParam': '', 'view': '', 'dynamicViewsCommentsSrc': '//www.blogblog.com/dynamicviews/4224c15c4e7c9321/js/comments.js', 'dynamicViewsScriptSrc': '//www.blogblog.com/dynamicviews/c4ef6ff9ae7c94eb', 'plusOneApiSrc': 'https://apis.google.com/js/platform.js', 'disableGComments': true, 'interstitialAccepted': false, 'sharing': {'platforms': [{'name': 'Get link', 'key': 'link', 'shareMessage': 'Get link', 'target': ''}, {'name': 'Facebook', 'key': 'facebook', 'shareMessage': 'Share to Facebook', 'target': 'facebook'}, {'name': 'BlogThis!', 'key': 'blogThis', 'shareMessage': 'BlogThis!', 'target': 'blog'}, {'name': 'X', 'key': 'twitter', 'shareMessage': 'Share to X', 'target': 'twitter'}, {'name': 'Pinterest', 'key': 'pinterest', 'shareMessage': 'Share to Pinterest', 'target': 'pinterest'}, {'name': 'Email', 'key': 'email', 'shareMessage': 'Email', 'target': 'email'}], 'disableGooglePlus': true, 'googlePlusShareButtonWidth': 0, 'googlePlusBootstrap': '\x3cscript type\x3d\x22text/javascript\x22\x3ewindow.___gcfg \x3d {\x27lang\x27: \x27en\x27};\x3c/script\x3e'}, 'hasCustomJumpLinkMessage': false, 'jumpLinkMessage': 'Read more', 'pageType': 'archive', 'pageName': '2020', 'pageTitle': 'Neal Gafter\x27s blog: 2020'}}, {'name': 'features', 'data': {}}, {'name': 'messages', 'data': {'edit': 'Edit', 'linkCopiedToClipboard': 'Link copied to clipboard!', 'ok': 'Ok', 'postLink': 'Post Link'}}, {'name': 'template', 'data': {'name': 'custom', 'localizedName': 'Custom', 'isResponsive': false, 'isAlternateRendering': false, 'isCustom': true}}, {'name': 'view', 'data': {'classic': {'name': 'classic', 'url': '?view\x3dclassic'}, 'flipcard': {'name': 'flipcard', 'url': '?view\x3dflipcard'}, 'magazine': {'name': 'magazine', 'url': '?view\x3dmagazine'}, 'mosaic': {'name': 'mosaic', 'url': '?view\x3dmosaic'}, 'sidebar': {'name': 'sidebar', 'url': '?view\x3dsidebar'}, 'snapshot': {'name': 'snapshot', 'url': '?view\x3dsnapshot'}, 'timeslide': {'name': 'timeslide', 'url': '?view\x3dtimeslide'}, 'isMobile': false, 'title': 'Neal Gafter\x27s blog', 'description': 'Thoughts about Programming Languages, Science and Philosophy.', 'url': 'https://gafter.blogspot.com/2020/', 'type': 'feed', 'isSingleItem': false, 'isMultipleItems': true, 'isError': false, 'isPage': false, 'isPost': false, 'isHomepage': false, 'isArchive': true, 'isLabelSearch': false, 'archive': {'year': 2020, 'rangeMessage': 'Showing posts from 2020'}}}]); 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