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231 lines
14 KiB
HTML
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<html>
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<title>Lists – Wren</title>
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<body id="top">
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<header>
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<div class="page">
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<div class="main-column">
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<h1><a href="./">wren</a></h1>
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<h2>a classy little scripting language</h2>
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</div>
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</div>
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</header>
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<div class="page">
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<nav class="big">
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<a href="./"><img src="./wren.svg" class="logo"></a>
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<ul>
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<li><a href="getting-started.html">Getting Started</a></li>
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<li><a href="contributing.html">Contributing</a></li>
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<li><a href="blog">Blog</a></li>
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</ul>
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<section>
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<h2>guides</h2>
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<ul>
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<li><a href="syntax.html">Syntax</a></li>
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<li><a href="values.html">Values</a></li>
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<li><a href="lists.html">Lists</a></li>
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<li><a href="maps.html">Maps</a></li>
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<li><a href="method-calls.html">Method Calls</a></li>
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<li><a href="control-flow.html">Control Flow</a></li>
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<li><a href="variables.html">Variables</a></li>
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<li><a href="functions.html">Functions</a></li>
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<li><a href="classes.html">Classes</a></li>
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<li><a href="concurrency.html">Concurrency</a></li>
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<li><a href="error-handling.html">Error Handling</a></li>
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<li><a href="modularity.html">Modularity</a></li>
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</ul>
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</section>
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<section>
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<h2>reference</h2>
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<ul>
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<li><a href="modules">Modules</a></li>
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<li><a href="embedding">Embedding</a></li>
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<li><a href="performance.html">Performance</a></li>
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<li><a href="qa.html">Q & A</a></li>
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<div><a href="getting-started.html">Getting Started</a></div>
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<div><a href="contributing.html">Contributing</a></div>
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<div><a href="blog">Blog</a></div>
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</tr>
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<tr>
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<td colspan="2"><h2>guides</h2></td>
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<td><h2>reference</h2></td>
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</tr>
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<tr>
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<td>
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<ul>
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<li><a href="syntax.html">Syntax</a></li>
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<li><a href="values.html">Values</a></li>
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<li><a href="lists.html">Lists</a></li>
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<li><a href="maps.html">Maps</a></li>
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<li><a href="method-calls.html">Method Calls</a></li>
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<li><a href="control-flow.html">Control Flow</a></li>
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</ul>
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</td>
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<td>
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<ul>
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<li><a href="variables.html">Variables</a></li>
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<li><a href="functions.html">Functions</a></li>
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<li><a href="classes.html">Classes</a></li>
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<li><a href="concurrency.html">Concurrency</a></li>
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<li><a href="error-handling.html">Error Handling</a></li>
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<li><a href="modularity.html">Modularity</a></li>
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</ul>
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</td>
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<td>
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<ul>
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<li><a href="modules">Modules</a></li>
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<li><a href="embedding">Embedding</a></li>
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<li><a href="performance.html">Performance</a></li>
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<li><a href="qa.html">Q & A</a></li>
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</ul>
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</td>
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</tr>
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</table>
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</nav>
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<main>
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<h2>Lists</h2>
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<p>A list is a compound object that holds a collection of elements identified by
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integer index. You can create a list by placing a sequence of comma-separated
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expressions inside square brackets: </p>
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<div class="codehilite"><pre><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="s">"banana"</span><span class="p">,</span> <span class="kc">true</span><span class="p">]</span>
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</pre></div>
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<p>Here, we’ve created a list of three elements. Notice that the elements don’t
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have to be the same type. </p>
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<h2>Accessing elements <a href="#accessing-elements" name="accessing-elements" class="header-anchor">#</a></h2>
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<p>You can access an element from a list by calling the <a href="method-calls.html#subscripts">subscript
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operator</a> on it with the index of the
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element you want. Like most languages, indexes start at zero: </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="n">hirsute</span> <span class="o">=</span> <span class="p">[</span><span class="s">"sideburns"</span><span class="p">,</span> <span class="s">"porkchops"</span><span class="p">,</span> <span class="s">"'stache"</span><span class="p">,</span> <span class="s">"goatee"</span><span class="p">]</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="output">sideburns</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span> <span class="output">porkchops</span>
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</pre></div>
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<p>Negative indices counts backwards from the end: </p>
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<div class="codehilite"><pre><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">])</span> <span class="output">goatee</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">[</span><span class="o">-</span><span class="mi">2</span><span class="p">])</span> <span class="output">'stache</span>
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</pre></div>
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<p>It’s a runtime error to pass an index outside of the bounds of the list. If you
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don’t know what those bounds are, you can find out using count: </p>
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<div class="codehilite"><pre><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="o">.</span><span class="n">count</span><span class="p">)</span> <span class="output">4</span>
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</pre></div>
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<h2>Slices and ranges <a href="#slices-and-ranges" name="slices-and-ranges" class="header-anchor">#</a></h2>
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<p>Sometimes you want to copy a chunk of elements from a list. You can do that by
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passing a <a href="values.html#ranges">range</a> to the subscript operator, like so: </p>
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<div class="codehilite"><pre><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">[</span><span class="mi">1</span><span class="o">..</span><span class="mi">2</span><span class="p">])</span> <span class="output">[porkchops, 'stache]</span>
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</pre></div>
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<p>This returns a new list containing the elements of the original list whose
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indices are within the given range. Both inclusive and exclusive ranges work
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and do what you expect. </p>
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<p>Negative bounds also work like they do when passing a single number, so to copy
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a list, you can just do: </p>
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<div class="codehilite"><pre><span class="n">hirsute</span><span class="p">[</span><span class="mi">0</span><span class="o">..-</span><span class="mi">1</span><span class="p">]</span>
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</pre></div>
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<h2>Adding elements <a href="#adding-elements" name="adding-elements" class="header-anchor">#</a></h2>
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<p>Lists are <em>mutable</em>, meaning their contents can be changed. You can swap out an
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existing element in the list using the subscript setter: </p>
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<div class="codehilite"><pre><span class="n">hirsute</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="s">"muttonchops"</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span> <span class="output">muttonchops</span>
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</pre></div>
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<p>It’s an error to set an element that’s out of bounds. To grow a list, you can
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use <code>add</code> to append a single item to the end: </p>
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<div class="codehilite"><pre><span class="n">hirsute</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="s">"goatee"</span><span class="p">)</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="o">.</span><span class="n">count</span><span class="p">)</span> <span class="output">5</span>
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</pre></div>
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<p>You can insert a new element at a specific position using <code>insert</code>: </p>
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<div class="codehilite"><pre><span class="n">hirsute</span><span class="o">.</span><span class="n">insert</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="s">"soul patch"</span><span class="p">)</span>
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</pre></div>
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<p>The first argument is the index to insert at, and the second is the value to
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insert. All elements following the inserted one will be pushed down to
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make room for it. </p>
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<p>It’s valid to “insert” after the last element in the list, but only <em>right</em>
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after it. Like other methods, you can use a negative index to count from the
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back. Doing so counts back from the size of the list <em>after</em> it’s grown by one: </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="n">letters</span> <span class="o">=</span> <span class="p">[</span><span class="s">"a"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">,</span> <span class="s">"c"</span><span class="p">]</span>
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<span class="n">letters</span><span class="o">.</span><span class="n">insert</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s">"d"</span><span class="p">)</span> <span class="c1">// OK: inserts at end.</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">letters</span><span class="p">)</span> <span class="output">[a, b, c, d]</span>
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<span class="n">letters</span><span class="o">.</span><span class="n">insert</span><span class="p">(</span><span class="o">-</span><span class="mi">2</span><span class="p">,</span> <span class="s">"e"</span><span class="p">)</span> <span class="c1">// Counts back from size after insert.</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">letters</span><span class="p">)</span> <span class="output">[a, b, c, e, d]</span>
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</pre></div>
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<h2>Adding lists together <a href="#adding-lists-together" name="adding-lists-together" class="header-anchor">#</a></h2>
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<p>Lists have the ability to be added together via the <code>+</code> operator. This is often known as concatenation. </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="n">letters</span> <span class="o">=</span> <span class="p">[</span><span class="s">"a"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">,</span> <span class="s">"c"</span><span class="p">]</span>
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<span class="k">var</span> <span class="n">other</span> <span class="o">=</span> <span class="p">[</span><span class="s">"d"</span><span class="p">,</span> <span class="s">"e"</span><span class="p">,</span> <span class="s">"f"</span><span class="p">]</span>
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<span class="k">var</span> <span class="n">combined</span> <span class="o">=</span> <span class="n">letters</span> <span class="o">+</span> <span class="n">other</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">combined</span><span class="p">)</span> <span class="output">[a, b, c, d, e, f]</span>
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</pre></div>
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<h2>Removing elements <a href="#removing-elements" name="removing-elements" class="header-anchor">#</a></h2>
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<p>The opposite of <code>insert</code> is <code>removeAt</code>. It removes a single element from a
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given position in the list. All following items are shifted up to fill in the
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gap: </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="n">letters</span> <span class="o">=</span> <span class="p">[</span><span class="s">"a"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">,</span> <span class="s">"c"</span><span class="p">,</span> <span class="s">"d"</span><span class="p">]</span>
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<span class="n">letters</span><span class="o">.</span><span class="n">removeAt</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">letters</span><span class="p">)</span> <span class="output">[a, c, d]</span>
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</pre></div>
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<p>The <code>removeAt</code> method returns the removed item: </p>
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<div class="codehilite"><pre><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">letters</span><span class="o">.</span><span class="n">removeAt</span><span class="p">(</span><span class="mi">1</span><span class="p">))</span> <span class="output">c</span>
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</pre></div>
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<p>If you want to remove everything from the list, you can clear it: </p>
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<div class="codehilite"><pre><span class="n">hirsute</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">hirsute</span><span class="p">)</span> <span class="output">[]</span>
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</pre></div>
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<p><br><hr>
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<a class="right" href="maps.html">Maps →</a>
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<a href="values.html">← Values</a> </p>
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<footer>
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<p>Wren lives
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<a href="https://github.com/wren-lang/wren">on GitHub</a>
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— Made with ❤ by
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<a href="http://journal.stuffwithstuff.com/">Bob Nystrom</a> and
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<a href="https://github.com/wren-lang/wren/blob/master/AUTHORS">friends</a>.
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