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<section class="normal markdown-section">
<h1 id="decorator-pattern">Decorator Pattern</h1>
<p>Decorator structural pattern allows extending the function of an existing object dynamically without altering its internals.</p>
<p>Decorators provide a flexible method to extend functionality of objects.</p>
<h2 id="implementation">Implementation</h2>
<p><code>LogDecorate</code> decorates a function with the signature <code>func(int) int</code> that
manipulates integers and adds input/output logging capabilities.</p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Object <span class="hljs-keyword">func</span>(<span class="hljs-keyword">int</span>) <span class="hljs-keyword">int</span>
<span class="hljs-keyword">func</span> LogDecorate(fn Object) Object {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">func</span>(n <span class="hljs-keyword">int</span>) <span class="hljs-keyword">int</span> {
log.Println(<span class="hljs-string">&quot;Starting the execution with the integer&quot;</span>, n)
result := fn(n)
log.Println(<span class="hljs-string">&quot;Execution is completed with the result&quot;</span>, result)
<span class="hljs-keyword">return</span> result
}
}
</code></pre>
<h2 id="usage">Usage</h2>
<pre><code class="lang-go"><span class="hljs-keyword">func</span> Double(n <span class="hljs-keyword">int</span>) <span class="hljs-keyword">int</span> {
<span class="hljs-keyword">return</span> n * <span class="hljs-number">2</span>
}
f := LogDecorate(Double)
f(<span class="hljs-number">5</span>)
<span class="hljs-comment">// Starting execution with the integer 5</span>
<span class="hljs-comment">// Execution is completed with the result 10</span>
</code></pre>
<h2 id="rules-of-thumb">Rules of Thumb</h2>
<ul>
<li>Unlike Adapter pattern, the object to be decorated is obtained by <strong>injection</strong>.</li>
<li>Decorators should not alter the interface of an object.</li>
</ul>
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