<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">Reposting comment from Dave A. in a previous thread:</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><span style="font-family: 'helvetica Neue', helvetica; font-size: 14px;">"I'm not sure how useful this is, because it's not really a comment on</span><br style="font-family: 'helvetica Neue', helvetica; font-size: 14px;"><span style="font-family: 'helvetica Neue', helvetica; font-size: 14px;">your efforts, but... some of us think we know how this problem domain</span><br style="font-family: 'helvetica Neue', helvetica; font-size: 14px;"><span style="font-family: 'helvetica Neue', helvetica; font-size: 14px;">*should* be addressed, and we know that Swift doesn't yet have the</span><br style="font-family: 'helvetica Neue', helvetica; font-size: 14px;"><span style="font-family: 'helvetica Neue', helvetica; font-size: 14px;">necessary language facilities (integer generic parameters) to do the job</span><br style="font-family: 'helvetica Neue', helvetica; font-size: 14px;"><span style="font-family: 'helvetica Neue', helvetica; font-size: 14px;">right. The technique was described back in 1994 by Barton & Nackman in</span><br style="font-family: 'helvetica Neue', helvetica; font-size: 14px;"><font face="helvetica Neue, helvetica"><span style="font-size: 14px;"><a href="https://www.amazon.com/Scientific-Engineering-Introduction-Advanced-Techniques/dp/0201533936">https://www.amazon.com/Scientific-Engineering-Introduction-Advanced-Techniques/dp/0201533936</a></span></font></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">“</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">We would have the ability to implement dimensional analysis library like the one in Boost today: http://www.boost.org/doc/libs/1_61_0/doc/html/boost_units.html</div> <br> <div id="bloop_sign_1471896626107877888" class="bloop_sign"><div>-- <br>Daniel Duan</div></div> <br><p class="airmail_on">On August 22, 2016 at 11:54:13 AM, David Sweeris via swift-evolution (<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div dir="auto"><div></div><div>
<title></title>
<div>Wasn't there something about "units" announced at wwdc that
does exactly this?<br>
<br>
Sent from my iPhone</div>
<div><br>
On Aug 22, 2016, at 09:54, Nur Ismail via swift-evolution
<<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>
wrote:<br>
<br></div>
<blockquote type="cite">
<div>
<div dir="ltr">
<div style="font-size:13px">Hi,</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">I'm new to the list, but have an idea
for Typed Numerics.</div>
<div style="font-size:13px">Basically numeric values (such as
Double, Int, etc.) that are strongly typed to a specific use case,
for example Distance, Weight, etc. and cannot be intermixed with
untyped values.</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">So if I have (the syntax is made up,
but perhaps something like this):</div>
<div style="font-size:13px">=====</div>
<div style="font-size:13px">
<div>//Distance</div>
<div>struct fixedtype Distance : Double {</div>
<div>var km: …</div>
<div>var m: …</div>
<div>typealias meters: m</div>
<div>var feet: ...</div>
<div>...</div>
<div>}</div>
<div><br></div>
<div>//Weight</div>
<div>struct fixedtype Weight : Double {</div>
<div>var kg: …</div>
<div>var g: …</div>
<div>typealias grams : g</div>
<div>var pound: ...</div>
<div>}</div>
<div><br></div>
<div>…</div>
<div>var weight : Weight = <a href="http://5.kg/" target="_blank">5.kg</a> + 5.g + 7.m</div>
<div>………………………………………..^ Compiler Error: Can’t add Distance to
Weight...</div>
<div>var distance: Distance = <a href="http://7.km/" target="_blank">7.km</a> + 12.5.m + 5.0 + 3</div>
<div>………………………………………………...^ Compiler Error: can’t add untyped
number to Distance...</div>
</div>
<div style="font-size:13px">===</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">The main restriction this syntax should
do is disallow intermixing of numeric types (even if they all
descend from Double, Int, etc.) and not allow adding untyped
numerics (i.e. those without a type suffix), unless explicitly
asked for in the code.</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">Any of these can be converted to it's
raw untyped value, for example:</div>
<div style="font-size:13px">=====</div>
<div style="font-size:13px">let number : Double = distance.rawValue
+ 5.0 //This is allowed</div>
<div style="font-size:13px">distance += number.m //number is
converted to m (meters)</div>
<div style="font-size:13px">=====</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">From the Swift 3 Language guide, we are
for example given the following example:</div>
<div style="font-size:13px">=====</div>
<div style="font-size:13px">extension Double {<br></div>
<div style="font-size:13px"> var km: Double { return self *
1_000.0 }</div>
<div style="font-size:13px"> var m: Double { return self
}</div>
<div style="font-size:13px"> var cm: Double { return self /
100.0 }</div>
<div style="font-size:13px"> var mm: Double { return self /
1_000.0 }</div>
<div style="font-size:13px"> var ft: Double { return self /
3.28084 }</div>
<div style="font-size:13px">}</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">
<div>let aMarathon = <a href="http://42.km/" target="_blank">42.km</a> + 195.m</div>
<div>print("A marathon is \(aMarathon) meters long")</div>
<div>// Prints "A marathon is 42195.0 meters long"</div>
</div>
<div style="font-size:13px">=====</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">This is quite nice to suffix a
conversion method after the value, but if I had another extension
that converts the values to pounds and kilograms, then one can
illegally do this:</div>
<div style="font-size:13px"> let aValue
= <a href="http://42.km/" target="_blank">42.km</a> +
195.m + 17.pounds + 5.0</div>
<div style="font-size:13px">and then the code would still compile
and run, but not work as intended.</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">Extra reading, and inspiration for a
feature like the above:</div>
<div style="font-size:13px">Mars Probe Lost Due to Simple Math
Error<br></div>
<div style="font-size:13px"><a href="http://articles.latimes.com/1999/oct/01/news/mn-17288" target="_blank">http://articles.latimes.com/<wbr>1999/oct/01/news/mn-17288</a><br>
</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">"NASA lost its $125-million Mars
Climate Orbiter because spacecraft engineers failed to convert from
English to metric measurements when exchanging vital data before
the craft was launched, space agency officials said Thursday.</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">A navigation team at the Jet Propulsion
Laboratory used the metric system of millimeters and meters in its
calculations, while Lockheed Martin Astronautics in Denver, which
designed and built the spacecraft, provided crucial acceleration
data in the English system of inches, feet and pounds.</div>
<div style="font-size:13px"><br></div>
<div style="font-size:13px">As a result, JPL engineers mistook
acceleration readings measured in English units of pound-seconds
for a metric measure of force called newton-seconds."</div>
</div>
</div>
</blockquote>
<blockquote type="cite">
<div>
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