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diff --git a/public/posts/2024-12-08-01.html b/public/posts/2024-12-08-01.html index a32f539..2631b69 100644 --- a/public/posts/2024-12-08-01.html +++ b/public/posts/2024-12-08-01.html @@ -25,72 +25,70 @@ <ul> - <li><a class="no-decorations" href="/">home</a></li> + <li><a class="no-decorations" href="/">Home</a></li> - <li><a class="no-decorations" href="/posts">posts</a></li> + <li><a class="no-decorations" href="/posts">Posts</a></li> - <li><a class="no-decorations" href="/ethos">ethos</a></li> + <li><a class="no-decorations" href="/ethos">Ethos</a></li> </ul> </nav> </div> + <hr /> <a href="/posts">← Posts</a> <h1>Simplifying Interfaces with Function Types</h1> +<h1 id="table-of-contents">Table of Contents</h1> +<ul> +<li> +<a href="#example">Example</a></li> +<li> +<a href="#how-it-works">How it works</a></li> +<li> +<a href="#application">Application</a></li> +</ul> <p>In Go, you can define methods on type aliases, which means that we can define a type alias of a function, and then define methods on that function.</p> - <h2 id="example">Example</h2> - <p>Given the following interface</p> -<pre tabindex="0" class="chroma"><code><span class="line"><span class="cl"><span class="kd">type</span> <span class="nx">DB</span> <span class="kd">interface</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="nf">Get</span><span class="p">(</span><span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="kt">string</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> -</span></span><span class="line"><span class="cl"><span class="p">}</span> -</span></span></code></pre> -<p>You can fulfill it using a function type like this:</p> -<pre tabindex="0" class="chroma"><code><span class="line"><span class="cl"><span class="kd">type</span> <span class="nx">GetFn</span> <span class="kd">func</span><span class="p">(</span><span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="kt">string</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> -</span></span><span class="line"><span class="cl"> -</span></span><span class="line"><span class="cl"><span class="kd">func</span> <span class="p">(</span><span class="nx">f</span> <span class="nx">GetFn</span><span class="p">)</span> <span class="nf">Get</span><span class="p">(</span><span class="nx">a</span> <span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="kt">string</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="nf">f</span><span class="p">(</span><span class="nx">a</span><span class="p">)</span> -</span></span><span class="line"><span class="cl"><span class="p">}</span> -</span></span></code></pre> -<p>Now you can use GetFn whenever a DB is required:</p> -<pre tabindex="0" class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="kd">var</span> <span class="nx">storeFn</span> <span class="nx">DB</span> <span class="p">=</span> <span class="nf">GetFn</span><span class="p">(</span><span class="kd">func</span><span class="p">(</span><span class="nx">s</span> <span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="kt">string</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="s">"bar"</span><span class="p">,</span> <span class="kc">nil</span> -</span></span><span class="line"><span class="cl"> <span class="p">})</span> -</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">storeFn</span><span class="p">.</span><span class="nf">Get</span><span class="p">(</span><span class="s">"Foo"</span><span class="p">))</span> <span class="c1">// Outputs: bar -</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="p">}</span> -</span></span></code></pre> -<p>You can try this example in this [Go Playground](<a href="https://go.dev/play/p/hyBNIMblafs">https://go.dev/play/p/hyBNIMblafs</a></p> +<pre tabindex="0" style="background-color:#f0f0f0;-moz-tab-size:4;-o-tab-size:4;tab-size:4;white-space:pre-wrap;word-break:break-word;"><code><span style="color:#00a">type</span> DB <span style="color:#00a">interface</span> { + <span style="color:#0a0">Get</span>(<span style="color:#0aa">string</span>) (<span style="color:#0aa">string</span>, <span style="color:#0aa">error</span>) +} +</code></pre><p>You can fulfill it using a function type like this:</p> +<pre tabindex="0" style="background-color:#f0f0f0;-moz-tab-size:4;-o-tab-size:4;tab-size:4;white-space:pre-wrap;word-break:break-word;"><code><span style="color:#00a">type</span> GetFn <span style="color:#00a">func</span>(<span style="color:#0aa">string</span>) (<span style="color:#0aa">string</span>, <span style="color:#0aa">error</span>) +<span style="color:#00a">func</span> (f GetFn) <span style="color:#0a0">Get</span>(a <span style="color:#0aa">string</span>) (<span style="color:#0aa">string</span>, <span style="color:#0aa">error</span>) { + <span style="color:#00a">return</span> <span style="color:#0a0">f</span>(a) +} +</code></pre><p>Now you can use GetFn whenever a DB is required:</p> +<pre tabindex="0" style="background-color:#f0f0f0;-moz-tab-size:4;-o-tab-size:4;tab-size:4;white-space:pre-wrap;word-break:break-word;"><code><span style="color:#00a">func</span> <span style="color:#0a0">main</span>() { + <span style="color:#00a">var</span> storeFn DB = <span style="color:#0a0">GetFn</span>(<span style="color:#00a">func</span>(s <span style="color:#0aa">string</span>) (<span style="color:#0aa">string</span>, <span style="color:#0aa">error</span>) { + <span style="color:#00a">return</span> <span style="color:#a50">"bar"</span>, <span style="color:#00a">nil</span> + }) + fmt.<span style="color:#0a0">Println</span>(storeFn.<span style="color:#0a0">Get</span>(<span style="color:#a50">"Foo"</span>)) <span style="color:#aaa;font-style:italic">// Outputs: bar +</span><span style="color:#aaa;font-style:italic"></span>} +</code></pre><p>You can try this example in this [Go Playground](<a href="https://go.dev/play/p/hyBNIMblafs">https://go.dev/play/p/hyBNIMblafs</a></p> <h2 id="how-it-works">How it works</h2> - <p>In Go, interfaces are implicitly through method sets, which means any type (including a function type) that defines the required methods satisfies the interface. By defining the <code>Get</code> method on the <code>GetFn</code> type, the compiler treats <code>GetFn</code> as a valid implementation of the DB interface.</p> - <p>This flexibility allows you to use function types as lightweight, dynamic implementations of interfaces, without the need for full struct definitions.</p> - <h2 id="application">Application</h2> - <p>One common use case for this pattern is testing. Instead of implementing a full mock, you can use an inline function to provide test specific behavior.</p> -<pre tabindex="0" class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">TestHandler</span><span class="p">()</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="nx">mockDB</span> <span class="o">:=</span> <span class="nf">GetFn</span><span class="p">(</span><span class="kd">func</span><span class="p">(</span><span class="nx">key</span> <span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="kt">string</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="k">if</span> <span class="nx">key</span> <span class="o">==</span> <span class="s">"foo"</span> <span class="p">{</span> -</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="s">"bar"</span><span class="p">,</span> <span class="kc">nil</span> -</span></span><span class="line"><span class="cl"> <span class="p">}</span> -</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="s">""</span><span class="p">,</span> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Errorf</span><span class="p">(</span><span class="s">"not found"</span><span class="p">)</span> -</span></span><span class="line"><span class="cl"> <span class="p">})</span> -</span></span><span class="line"><span class="cl"> -</span></span><span class="line"><span class="cl"> <span class="nx">result</span><span class="p">,</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">mockDB</span><span class="p">.</span><span class="nf">Get</span><span class="p">(</span><span class="s">"foo"</span><span class="p">)</span> -</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">result</span><span class="p">,</span> <span class="nx">err</span><span class="p">)</span> <span class="c1">// Outputs: bar, <nil> -</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="p">}</span> -</span></span></code></pre> -<p>This approach is not limited to testing. It’s also useful for dependency injection, where you can pass in lightweight or context specific implementations of an interface.</p> +<pre tabindex="0" style="background-color:#f0f0f0;-moz-tab-size:4;-o-tab-size:4;tab-size:4;white-space:pre-wrap;word-break:break-word;"><code><span style="color:#00a">func</span> <span style="color:#0a0">TestHandler</span>() { + mockDB := <span style="color:#0a0">GetFn</span>(<span style="color:#00a">func</span>(key <span style="color:#0aa">string</span>) (<span style="color:#0aa">string</span>, <span style="color:#0aa">error</span>) { + <span style="color:#00a">if</span> key == <span style="color:#a50">"foo"</span> { + <span style="color:#00a">return</span> <span style="color:#a50">"bar"</span>, <span style="color:#00a">nil</span> + } + <span style="color:#00a">return</span> <span style="color:#a50">""</span>, fmt.<span style="color:#0a0">Errorf</span>(<span style="color:#a50">"not found"</span>) + }) + result, err := mockDB.<span style="color:#0a0">Get</span>(<span style="color:#a50">"foo"</span>) + fmt.<span style="color:#0a0">Println</span>(result, err) <span style="color:#aaa;font-style:italic">// Outputs: bar, <nil> +</span><span style="color:#aaa;font-style:italic"></span>} +</code></pre><p>This approach is not limited to testing. It’s also useful for dependency injection, where you can pass in lightweight or context specific implementations of an interface.</p> <p>This pattern is similar to how <code>http.HandleFunc</code> works. In the HTTP package, <code>http.HandlerFunc</code> is a function type that fulfills the <code>http.Handler</code> interface by implementing its <code>ServeHTTP</code> method. This allows functions to act as handlers, providing great flexibility in designing web servers.</p> |