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Travis CI | 67efe3e Merge pull request #26 from Philiphil/patch-1
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<h1 id="observer-pattern">Observer Pattern</h1>
<p>The <a href="https://en.wikipedia.org/wiki/Observer_pattern" target="_blank">observer pattern</a> allows a type instance to &quot;publish&quot; events to other type instances (&quot;observers&quot;) who wish to be updated when a particular event occurs.</p>
<h2 id="implementation">Implementation</h2>
<p>In long-running applications&#x2014;such as webservers&#x2014;instances can keep a collection of observers that will receive notification of triggered events.</p>
<p>Implementations vary, but interfaces can be used to make standard observers and notifiers:</p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> (
<span class="hljs-comment">// Event defines an indication of a point-in-time occurrence.</span>
Event <span class="hljs-keyword">struct</span> {
<span class="hljs-comment">// Data in this case is a simple int, but the actual</span>
<span class="hljs-comment">// implementation would depend on the application.</span>
Data <span class="hljs-keyword">int64</span>
}
<span class="hljs-comment">// Observer defines a standard interface for instances that wish to list for</span>
<span class="hljs-comment">// the occurrence of a specific event.</span>
Observer <span class="hljs-keyword">interface</span> {
<span class="hljs-comment">// OnNotify allows an event to be &quot;published&quot; to interface implementations.</span>
<span class="hljs-comment">// In the &quot;real world&quot;, error handling would likely be implemented.</span>
OnNotify(Event)
}
<span class="hljs-comment">// Notifier is the instance being observed. Publisher is perhaps another decent</span>
<span class="hljs-comment">// name, but naming things is hard.</span>
Notifier <span class="hljs-keyword">interface</span> {
<span class="hljs-comment">// Register allows an instance to register itself to listen/observe</span>
<span class="hljs-comment">// events.</span>
Register(Observer)
<span class="hljs-comment">// Deregister allows an instance to remove itself from the collection</span>
<span class="hljs-comment">// of observers/listeners.</span>
Deregister(Observer)
<span class="hljs-comment">// Notify publishes new events to listeners. The method is not</span>
<span class="hljs-comment">// absolutely necessary, as each implementation could define this itself</span>
<span class="hljs-comment">// without losing functionality.</span>
Notify(Event)
}
)
</code></pre>
<h2 id="usage">Usage</h2>
<p>For usage, see <a href="observer/main.go">observer/main.go</a> or <a href="https://play.golang.org/p/cr8jEmDmw0" target="_blank">view in the Playground</a>.</p>
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