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Merge pull request #1277 from ashawley/cheatsheet-options
Add Option to cheatsheet
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‎_overviews/cheatsheets/index.md

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@@ -294,27 +294,27 @@ yield x * y</code></pre>
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<tr>
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<td><span class="label important">Bad</span><br>
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<pre class="highlight"><code>val v42 = 42
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Some(3) match {
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case Some(v42) =&gt; println("42")
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case _ =&gt; println("Not 42")
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3 match {
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case v42 =&gt; println("42")
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case _ =&gt; println("Not 42")
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}</code></pre></td>
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<td>“v42” is interpreted as a name matching any Int value, and “42” is printed.</td>
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</tr>
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<tr>
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<td><span class="label success">Good</span><br>
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<pre class="highlight"><code>val v42 = 42
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Some(3) match {
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case Some(`v42`) =&gt; println("42")
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case _ =&gt; println("Not 42")
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3 match {
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case `v42` =&gt; println("42")
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case _ =&gt; println("Not 42")
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}</code></pre></td>
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<td>”`v42`” with backticks is interpreted as the existing val <pre class="highlight"><code>v42</code></pre>, and “Not 42” is printed.</td>
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<td><span class="label success">Good</span><br>
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<pre class="highlight"><code>val UppercaseVal = 42
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Some(3) match {
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case Some(UppercaseVal) =&gt; println("42")
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case _ =&gt; println("Not 42")
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3 match {
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case UppercaseVal =&gt; println("42")
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case _ =&gt; println("Not 42")
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}</code></pre></td>
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<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>
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@@ -397,6 +397,231 @@ Some(3) match {
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<tr>
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<td><pre class="highlight"><code>x: String</code></pre></td>
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<td>ascription (compile time)</td>
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<td> </td>
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</tr>
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<tr>
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<td><span id="options" class="h2">options</span></td>
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<td> </td>
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</tr>
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<td><pre class="highlight"><code>Some(42)</code></pre></td>
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<td>Construct a non empty optional value</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>None</code></pre></td>
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<td>The singleton empty optional value</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>Option(null) == None
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Option(obj.unsafeMethod)</code></pre></td>
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<td>Null-safe optional value factory</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>val optStr: Option[String] = None</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>val optStr = Option.empty[String]</code></pre></td>
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<td>Explicit type for empty optional value.<br /> Factory for empty optional value.</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>val name: Option[String] =
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request.getParameter("name")
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val upper = name.map {
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_.trim
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}
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.filter {
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_.length != 0
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}
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.map {
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_.toUpperCase
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}
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println(upper.getOrElse(""))
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</code></pre></td>
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<td>Pipeline style</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>val upper = for {
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name <- request.getParameter("name")
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trimmed <- Some(name.trim)
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if trimmed.length != 0
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upper <- Some(trimmed.toUpperCase)
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} yield upper
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println(upper.getOrElse(""))</code></pre></td>
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<td>for-comprehension syntax</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.map(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; Some(f(x))
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case None =&gt; None
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}</code></pre></td>
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<td>Apply a function on the optional value</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.flatMap(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; f(x)
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case None =&gt; None
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}</code></pre></td>
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<td>Same as map but function must return an optional value</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>optionOfOption.flatten</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>optionOfOption match {
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case Some(Some(x)) =&gt; Some(x)
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case _ =&gt; None
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}</code></pre></td>
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<td>Extract nested option</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.foreach(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; f(x)
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case None =&gt; ()
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}</code></pre></td>
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<td>Apply a procedure on optional value</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.fold(y)(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; f(x)
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case None =&gt; y
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}</code></pre></td>
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<td>Apply function on optional value, return default if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.collect {
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case x =&gt; ...
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}</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x)
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if f.isDefinedAt(x) =&gt; ...
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case Some(_) =&gt; None
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case None =&gt; None
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}</code></pre></td>
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<td>Apply partial pattern match on optional value</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.isDefined</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(_) =&gt; true
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case None =&gt; false
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}</code></pre></td>
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<td>True if not empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.isEmpty</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(_) =&gt; false
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case None =&gt; true
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}</code></pre></td>
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<td>True if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.nonEmpty</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(_) =&gt; true
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case None =&gt; false
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}</code></pre></td>
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<td>True if not empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.size</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(_) =&gt; 1
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case None =&gt; 0
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}</code></pre></td>
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<td>Zero if empty, otherwise one</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.orElse(Some(y))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; Some(x)
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case None =&gt; Some(y)
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}</code></pre></td>
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<td>Evaluate and return alternate optional value if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.getOrElse(y)</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; x
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case None =&gt; y
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}</code></pre></td>
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<td>Evaluate and return default value if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.get</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; x
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case None =&gt; throw new Exception
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}</code></pre></td>
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<td>Return value, throw exception if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.orNull</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; x
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case None =&gt; null
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}</code></pre></td>
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<td>Return value, null if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.filter(f)</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) if f(x) =&gt; Some(x)
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case _ =&gt; None
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}</code></pre></td>
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<td>Optional value satisfies predicate</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.filterNot(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) if !f(x) =&gt; Some(x)
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case _ =&gt; None
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}</code></pre></td>
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<td>Optional value doesn't satisfy predicate</td>
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</tr>
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<td><pre class="highlight"><code>option.exists(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) if f(x) =&gt; true
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case _ =&gt; false
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}</code></pre></td>
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<td>Apply predicate on optional value or false if empty</td>
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</tr>
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<tr>
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<td><pre class="highlight"><code>option.forall(f(_))</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) if f(x) =&gt; true
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case None =&gt; false
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}</code></pre></td>
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<td>Apply predicate on optional value or true if empty</td>
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</tr>
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<td><pre class="highlight"><code>option.contains(y)</code></pre>
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<em><strong>same as</strong></em>
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<pre class="highlight"><code>option match {
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case Some(x) =&gt; x == y
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case None =&gt; false
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}</code></pre></td>
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<td>Checks if value equals optional value or false if empty</td>
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</tbody>
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</table>

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