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Add Option to cheatsheet #1277

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Feb 8, 2019
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Add Option to cheatsheet #1277

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243 changes: 234 additions & 9 deletions _overviews/cheatsheets/index.md
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Original file line number Diff line number Diff line change
Expand Up @@ -294,27 +294,27 @@ yield x * y</code></pre>
<tr>
<td><span class="label important">Bad</span><br>
<pre class="highlight"><code>val v42 = 42
Some(3) match {
case Some(v42) =&gt; println("42")
case _ =&gt; println("Not 42")
3 match {
case v42 =&gt; println("42")
case _ =&gt; println("Not 42")
}</code></pre></td>
<td>“v42” is interpreted as a name matching any Int value, and “42” is printed.</td>
</tr>
<tr>
<td><span class="label success">Good</span><br>
<pre class="highlight"><code>val v42 = 42
Some(3) match {
case Some(`v42`) =&gt; println("42")
case _ =&gt; println("Not 42")
3 match {
case `v42` =&gt; println("42")
case _ =&gt; println("Not 42")
}</code></pre></td>
<td>”`v42`” with backticks is interpreted as the existing val <pre class="highlight"><code>v42</code></pre>, and “Not 42” is printed.</td>
</tr>
<tr>
<td><span class="label success">Good</span><br>
<pre class="highlight"><code>val UppercaseVal = 42
Some(3) match {
case Some(UppercaseVal) =&gt; println("42")
case _ =&gt; println("Not 42")
3 match {
case UppercaseVal =&gt; println("42")
case _ =&gt; println("Not 42")
}</code></pre></td>
<td><pre class="highlight"><code>UppercaseVal</code></pre> is treated as an existing val, rather than a new pattern variable, because it starts with an uppercase letter. Thus, the value contained within <pre class="highlight"><code>UppercaseVal</code></pre> is checked against <pre class="highlight"><code>3</code></pre>, and “Not 42” is printed.</td>
</tr>
Expand Down Expand Up @@ -397,6 +397,231 @@ Some(3) match {
<tr>
<td><pre class="highlight"><code>x: String</code></pre></td>
<td>ascription (compile time)</td>
<td> </td>
</tr>
<tr>
<td><span id="options" class="h2">options</span></td>
<td> </td>
</tr>
<tr>
<td><pre class="highlight"><code>Some(42)</code></pre></td>
<td>Construct a non empty optional value</td>
</tr>
<tr>
<td><pre class="highlight"><code>None</code></pre></td>
<td>The singleton empty optional value</td>
</tr>
<tr>
<td><pre class="highlight"><code>Option(null) == None
Option(obj.unsafeMethod)</code></pre></td>
<td>Null-safe optional value factory</td>
</tr>
<tr>
<td><pre class="highlight"><code>val optStr: Option[String] = None</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>val optStr = Option.empty[String]</code></pre></td>
<td>Explicit type for empty optional value.<br /> Factory for empty optional value.</td>
</tr>
<tr>
<td><pre class="highlight"><code>val name: Option[String] =
request.getParameter("name")
val upper = name.map {
_.trim
}
.filter {
_.length != 0
}
.map {
_.toUpperCase
}
println(upper.getOrElse(""))
</code></pre></td>
<td>Pipeline style</td>
</tr>
<tr>
<td><pre class="highlight"><code>val upper = for {
name <- request.getParameter("name")
trimmed <- Some(name.trim)
if trimmed.length != 0
upper <- Some(trimmed.toUpperCase)
} yield upper
println(upper.getOrElse(""))</code></pre></td>
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do we really need to println something?

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It's not required, but it seems useful to show that the value is no longer an Option. Many of the other examples in the cheatsheet use println.

<td>for-comprehension syntax</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.map(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; Some(f(x))
case None =&gt; None
}</code></pre></td>
<td>Apply a function on the optional value</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.flatMap(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; f(x)
case None =&gt; None
}</code></pre></td>
<td>Same as map but function must return an optional value</td>
</tr>
<tr>
<td><pre class="highlight"><code>optionOfOption.flatten</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>optionOfOption match {
case Some(Some(x)) =&gt; Some(x)
case _ =&gt; None
}</code></pre></td>
<td>Extract nested option</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.foreach(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; f(x)
case None =&gt; ()
}</code></pre></td>
<td>Apply a procedure on optional value</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.fold(y)(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; f(x)
case None =&gt; y
}</code></pre></td>
<td>Apply function on optional value, return default if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.collect {
case x =&gt; ...
}</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x)
if f.isDefinedAt(x) =&gt; ...
case Some(_) =&gt; None
case None =&gt; None
}</code></pre></td>
<td>Apply partial pattern match on optional value</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.isDefined</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(_) =&gt; true
case None =&gt; false
}</code></pre></td>
<td>True if not empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.isEmpty</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(_) =&gt; false
case None =&gt; true
}</code></pre></td>
<td>True if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.nonEmpty</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(_) =&gt; true
case None =&gt; false
}</code></pre></td>
<td>True if not empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.size</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(_) =&gt; 1
case None =&gt; 0
}</code></pre></td>
<td>Zero if empty, otherwise one</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.orElse(Some(y))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; Some(x)
case None =&gt; Some(y)
}</code></pre></td>
<td>Evaluate and return alternate optional value if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.getOrElse(y)</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; x
case None =&gt; y
}</code></pre></td>
<td>Evaluate and return default value if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.get</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; x
case None =&gt; throw new Exception
}</code></pre></td>
<td>Return value, throw exception if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.orNull</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; x
case None =&gt; null
}</code></pre></td>
<td>Return value, null if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.filter(f)</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) if f(x) =&gt; Some(x)
case _ =&gt; None
}</code></pre></td>
<td>Optional value satisfies predicate</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.filterNot(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) if !f(x) =&gt; Some(x)
case _ =&gt; None
}</code></pre></td>
<td>Optional value doesn't satisfy predicate</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.exists(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) if f(x) =&gt; true
case _ =&gt; false
}</code></pre></td>
<td>Apply predicate on optional value or false if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.forall(f(_))</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) if f(x) =&gt; true
case None =&gt; false
}</code></pre></td>
<td>Apply predicate on optional value or true if empty</td>
</tr>
<tr>
<td><pre class="highlight"><code>option.contains(y)</code></pre>
<em><strong>same as</strong></em>
<pre class="highlight"><code>option match {
case Some(x) =&gt; x == y
case None =&gt; false
}</code></pre></td>
<td>Checks if value equals optional value or false if empty</td>
</tr>
</tbody>
</table>