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Bob Nystrom
2018-07-13 09:03:56 -07:00
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maps.html
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@ -100,12 +100,13 @@ maps a <em>key</em> to a <em>value</em>. The same data structure has a variety o
other languages: hash table, dictionary, association, table, etc. </p>
<p>You can create a map by placing a series of comma-separated entries inside
curly braces. Each entry is a key and a value separated by a colon: </p>
<pre class="codehilite"><code class="language-wren">{
<div class="codehilite"><pre><span></span>{
&quot;George&quot;: &quot;Harrison&quot;,
&quot;John&quot;: &quot;Lennon&quot;,
&quot;Paul&quot;: &quot;McCartney&quot;,
&quot;Ringo&quot;: &quot;Starr&quot;
}</code></pre>
}
</pre></div>
<p>This creates a map that associates the first name of each Beatle with his last
@ -123,10 +124,11 @@ time, even in very large maps. Since Wren only knows how to hash certain
built-in types, only those can be used as keys. </p>
<h2>Adding entries <a href="#adding-entries" name="adding-entries" class="header-anchor">#</a></h2>
<p>You add new key-value pairs to the map using the <a href="method-calls.html#subscripts">subscript operator</a>: </p>
<pre class="codehilite"><code class="language-wren">var capitals = {}
<div class="codehilite"><pre><span></span>var capitals = {}
capitals[&quot;Georgia&quot;] = &quot;Atlanta&quot;
capitals[&quot;Idaho&quot;] = &quot;Boise&quot;
capitals[&quot;Maine&quot;] = &quot;Augusta&quot;</code></pre>
capitals[&quot;Maine&quot;] = &quot;Augusta&quot;
</pre></div>
<p>If the key isn&rsquo;t already present, this adds it and associates it with the given
@ -134,41 +136,47 @@ value. If the key is already there, this just replaces its value. </p>
<h2>Looking up values <a href="#looking-up-values" name="looking-up-values" class="header-anchor">#</a></h2>
<p>To find the value associated with some key, again you use your friend the
subscript operator: </p>
<pre class="codehilite"><code class="language-wren">System.print(capitals[&quot;Idaho&quot;]) //&gt; Boise</code></pre>
<div class="codehilite"><pre><span></span>System.print(capitals[&quot;Idaho&quot;]) //&gt; Boise
</pre></div>
<p>If the key is present, this returns its value. Otherwise, it returns <code>null</code>. Of
course, <code>null</code> itself can also be used as a value, so seeing <code>null</code> here
doesn&rsquo;t necessarily mean the key wasn&rsquo;t found. </p>
<p>To tell definitively if a key exists, you can call <code>containsKey()</code>: </p>
<pre class="codehilite"><code class="language-wren">var belief = {&quot;nihilism&quot;: null}
<div class="codehilite"><pre><span></span>var belief = {&quot;nihilism&quot;: null}
System.print(belief[&quot;nihilism&quot;]) //&gt; null (though key exists)
System.print(belief[&quot;solipsism&quot;]) //&gt; null
System.print(belief.containsKey(&quot;nihilism&quot;)) //&gt; true
System.print(belief.containsKey(&quot;solipsism&quot;)) //&gt; false</code></pre>
System.print(belief.containsKey(&quot;solipsism&quot;)) //&gt; false
</pre></div>
<p>You can see how many entries a map contains using <code>count</code>: </p>
<pre class="codehilite"><code class="language-wren">System.print(capitals.count) //&gt; 3</code></pre>
<div class="codehilite"><pre><span></span>System.print(capitals.count) //&gt; 3
</pre></div>
<h2>Removing entries <a href="#removing-entries" name="removing-entries" class="header-anchor">#</a></h2>
<p>To remove an entry from a map, call <code>remove()</code> and pass in the key for the
entry you want to delete: </p>
<pre class="codehilite"><code class="language-wren">capitals.remove(&quot;Maine&quot;)
System.print(capitals.containsKey(&quot;Maine&quot;)) //&gt; false</code></pre>
<div class="codehilite"><pre><span></span>capitals.remove(&quot;Maine&quot;)
System.print(capitals.containsKey(&quot;Maine&quot;)) //&gt; false
</pre></div>
<p>If the key was found, this returns the value that was associated with it: </p>
<pre class="codehilite"><code class="language-wren">System.print(capitals.remove(&quot;Georgia&quot;)) //&gt; Atlanta</code></pre>
<div class="codehilite"><pre><span></span>System.print(capitals.remove(&quot;Georgia&quot;)) //&gt; Atlanta
</pre></div>
<p>If the key wasn&rsquo;t in the map to begin with, <code>remove()</code> just returns <code>null</code>. </p>
<p>If you want to remove <em>everything</em> from the map, like with <a href="lists.html">lists</a>, you call
<code>clear()</code>: </p>
<pre class="codehilite"><code class="language-wren">capitals.clear()
System.print(capitals.count) //&gt; 0</code></pre>
<div class="codehilite"><pre><span></span>capitals.clear()
System.print(capitals.count) //&gt; 0
</pre></div>
<h2>Iterating over the contents <a href="#iterating-over-the-contents" name="iterating-over-the-contents" class="header-anchor">#</a></h2>
@ -179,7 +187,7 @@ For that, map exposes two methods: <code>keys</code> and <code>values</code>. </
map, and the second returns one that iterates over the values. </p>
<p>If you want to see all of the key-value pairs in a map, the easiest way is to
iterate over the keys and use each to look up its value: </p>
<pre class="codehilite"><code class="language-wren">var birds = {
<div class="codehilite"><pre><span></span>var birds = {
&quot;Arizona&quot;: &quot;Cactus wren&quot;,
&quot;Hawaii&quot;: &quot;Nēnē&quot;,
&quot;Ohio&quot;: &quot;Northern Cardinal&quot;
@ -187,7 +195,8 @@ iterate over the keys and use each to look up its value: </p>
for (state in birds.keys) {
System.print(&quot;The state bird of &quot; + state + &quot; is &quot; + birds[state])
}</code></pre>
}
</pre></div>
<p>This program prints the three states and their birds. However, the <em>order</em>