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54<h3 id="lack-of-sum-types">Lack of Sum types</h3> 54<h3 id="lack-of-sum-types">Lack of Sum types</h3>
55<p>A “Sum” type is a data type that can hold one of many states at a given time, similar to how a boolean can hold a true or a false, not too different from an <code>enum</code> type in C. Go lacks <code>enum</code> types unfortunately, and you are forced to resort to crafting your own substitute.</p> 55<p>A “Sum” type is a data type that can hold one of many states at a given time, similar to how a boolean can hold a true or a false, not too different from an <code>enum</code> type in C. Go lacks <code>enum</code> types unfortunately, and you are forced to resort to crafting your own substitute.</p>
56<p>A type to represent gender for example:</p> 56<p>A type to represent gender for example:</p>
57<div class="sourceCode" id="cb1"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true"></a><span class="kw">type</span> Gender <span class="dt">int</span></span> 57<div class="sourceCode" id="cb1"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> Gender <span class="dt">int</span></span>
58<span id="cb1-2"><a href="#cb1-2" aria-hidden="true"></a></span> 58<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a></span>
59<span id="cb1-3"><a href="#cb1-3" aria-hidden="true"></a><span class="kw">const</span> (</span> 59<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="kw">const</span> <span class="op">(</span></span>
60<span id="cb1-4"><a href="#cb1-4" aria-hidden="true"></a> Male Gender = <span class="ot">iota</span> <span class="co">// assigns Male to 0</span></span> 60<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a> Male Gender <span class="op">=</span> <span class="ot">iota</span> <span class="co">// assigns Male to 0</span></span>
61<span id="cb1-5"><a href="#cb1-5" aria-hidden="true"></a> Female <span class="co">// assigns Female to 1</span></span> 61<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a> Female <span class="co">// assigns Female to 1</span></span>
62<span id="cb1-6"><a href="#cb1-6" aria-hidden="true"></a> Other <span class="co">// assigns Other to 2</span></span> 62<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a> Other <span class="co">// assigns Other to 2</span></span>
63<span id="cb1-7"><a href="#cb1-7" aria-hidden="true"></a>)</span> 63<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a><span class="op">)</span></span>
64<span id="cb1-8"><a href="#cb1-8" aria-hidden="true"></a></span> 64<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a></span>
65<span id="cb1-9"><a href="#cb1-9" aria-hidden="true"></a>fmt.Println(<span class="st">&quot;My gender is &quot;</span>, Male)</span> 65<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a>fmt<span class="op">.</span>Println<span class="op">(</span><span class="st">&quot;My gender is &quot;</span><span class="op">,</span> Male<span class="op">)</span></span>
66<span id="cb1-10"><a href="#cb1-10" aria-hidden="true"></a><span class="co">// My gender is 0</span></span> 66<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a><span class="co">// My gender is 0</span></span>
67<span id="cb1-11"><a href="#cb1-11" aria-hidden="true"></a><span class="co">// Oops! We have to implement String() for Gender ...</span></span> 67<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a><span class="co">// Oops! We have to implement String() for Gender ...</span></span>
68<span id="cb1-12"><a href="#cb1-12" aria-hidden="true"></a></span> 68<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a></span>
69<span id="cb1-13"><a href="#cb1-13" aria-hidden="true"></a><span class="kw">func</span> (g Gender) String() <span class="dt">string</span> {</span> 69<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a><span class="kw">func</span> <span class="op">(</span>g Gender<span class="op">)</span> String<span class="op">()</span> <span class="dt">string</span> <span class="op">{</span></span>
70<span id="cb1-14"><a href="#cb1-14" aria-hidden="true"></a> <span class="kw">switch</span> (g) {</span> 70<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a> <span class="kw">switch</span> <span class="op">(</span>g<span class="op">)</span> <span class="op">{</span></span>
71<span id="cb1-15"><a href="#cb1-15" aria-hidden="true"></a> <span class="kw">case</span> <span class="dv">0</span>: <span class="kw">return</span> <span class="st">&quot;Male&quot;</span></span> 71<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a> <span class="kw">case</span> <span class="dv">0</span><span class="op">:</span> <span class="kw">return</span> <span class="st">&quot;Male&quot;</span></span>
72<span id="cb1-16"><a href="#cb1-16" aria-hidden="true"></a> <span class="kw">case</span> <span class="dv">1</span>: <span class="kw">return</span> <span class="st">&quot;Female&quot;</span></span> 72<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a> <span class="kw">case</span> <span class="dv">1</span><span class="op">:</span> <span class="kw">return</span> <span class="st">&quot;Female&quot;</span></span>
73<span id="cb1-17"><a href="#cb1-17" aria-hidden="true"></a> <span class="kw">default</span>: <span class="kw">return</span> <span class="st">&quot;Other&quot;</span></span> 73<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a> <span class="kw">default</span><span class="op">:</span> <span class="kw">return</span> <span class="st">&quot;Other&quot;</span></span>
74<span id="cb1-18"><a href="#cb1-18" aria-hidden="true"></a> }</span> 74<span id="cb1-18"><a href="#cb1-18" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span>
75<span id="cb1-19"><a href="#cb1-19" aria-hidden="true"></a>}</span> 75<span id="cb1-19"><a href="#cb1-19" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
76<span id="cb1-20"><a href="#cb1-20" aria-hidden="true"></a></span> 76<span id="cb1-20"><a href="#cb1-20" aria-hidden="true" tabindex="-1"></a></span>
77<span id="cb1-21"><a href="#cb1-21" aria-hidden="true"></a><span class="co">// You can accidentally do stupid stuff like:</span></span> 77<span id="cb1-21"><a href="#cb1-21" aria-hidden="true" tabindex="-1"></a><span class="co">// You can accidentally do stupid stuff like:</span></span>
78<span id="cb1-22"><a href="#cb1-22" aria-hidden="true"></a>gender := Male + <span class="dv">1</span></span></code></pre></div> 78<span id="cb1-22"><a href="#cb1-22" aria-hidden="true" tabindex="-1"></a>gender <span class="op">:=</span> Male <span class="op">+</span> <span class="dv">1</span></span></code></pre></div>
79<p>The Haskell equivalent of the same:</p> 79<p>The Haskell equivalent of the same:</p>
80<div class="sourceCode" id="cb2"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true"></a><span class="kw">data</span> <span class="dt">Gender</span> <span class="ot">=</span> <span class="dt">Male</span></span> 80<div class="sourceCode" id="cb2"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="kw">data</span> <span class="dt">Gender</span> <span class="ot">=</span> <span class="dt">Male</span></span>
81<span id="cb2-2"><a href="#cb2-2" aria-hidden="true"></a> <span class="op">|</span> <span class="dt">Female</span></span> 81<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a> <span class="op">|</span> <span class="dt">Female</span></span>
82<span id="cb2-3"><a href="#cb2-3" aria-hidden="true"></a> <span class="op">|</span> <span class="dt">Other</span></span> 82<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a> <span class="op">|</span> <span class="dt">Other</span></span>
83<span id="cb2-4"><a href="#cb2-4" aria-hidden="true"></a> <span class="kw">deriving</span> (<span class="dt">Show</span>)</span> 83<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">deriving</span> (<span class="dt">Show</span>)</span>
84<span id="cb2-5"><a href="#cb2-5" aria-hidden="true"></a></span> 84<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a></span>
85<span id="cb2-6"><a href="#cb2-6" aria-hidden="true"></a><span class="fu">print</span> <span class="op">$</span> <span class="st">&quot;My gender is &quot;</span> <span class="op">++</span> (<span class="fu">show</span> <span class="dt">Male</span>)</span></code></pre></div> 85<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a><span class="fu">print</span> <span class="op">$</span> <span class="st">&quot;My gender is &quot;</span> <span class="op">++</span> (<span class="fu">show</span> <span class="dt">Male</span>)</span></code></pre></div>
86<h3 id="type-assertions">Type Assertions</h3> 86<h3 id="type-assertions">Type Assertions</h3>
87<p>A downcast with an optional error check? What could go wrong?</p> 87<p>A downcast with an optional error check? What could go wrong?</p>
88<p>Type assertions in Go allow you to do:</p> 88<p>Type assertions in Go allow you to do:</p>
89<div class="sourceCode" id="cb3"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true"></a><span class="kw">var</span> x <span class="kw">interface</span>{} = <span class="dv">7</span></span> 89<div class="sourceCode" id="cb3"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="kw">var</span> x <span class="kw">interface</span><span class="op">{}</span> <span class="op">=</span> <span class="dv">7</span></span>
90<span id="cb3-2"><a href="#cb3-2" aria-hidden="true"></a>y, goodToGo := x.(<span class="dt">int</span>)</span> 90<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a>y<span class="op">,</span> goodToGo <span class="op">:=</span> x<span class="op">.(</span><span class="dt">int</span><span class="op">)</span></span>
91<span id="cb3-3"><a href="#cb3-3" aria-hidden="true"></a><span class="kw">if</span> goodToGo {</span> 91<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="kw">if</span> goodToGo <span class="op">{</span></span>
92<span id="cb3-4"><a href="#cb3-4" aria-hidden="true"></a> fmt.Println(y)</span> 92<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a> fmt<span class="op">.</span>Println<span class="op">(</span>y<span class="op">)</span></span>
93<span id="cb3-5"><a href="#cb3-5" aria-hidden="true"></a>}</span></code></pre></div> 93<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
94<p>The error check however is optional:</p> 94<p>The error check however is optional:</p>
95<div class="sourceCode" id="cb4"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true"></a><span class="kw">var</span> x <span class="kw">interface</span>{} = <span class="dv">7</span></span> 95<div class="sourceCode" id="cb4"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="kw">var</span> x <span class="kw">interface</span><span class="op">{}</span> <span class="op">=</span> <span class="dv">7</span></span>
96<span id="cb4-2"><a href="#cb4-2" aria-hidden="true"></a><span class="kw">var</span> y := x.(<span class="dt">float64</span>)</span> 96<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="kw">var</span> y <span class="op">:=</span> x<span class="op">.(</span><span class="dt">float64</span><span class="op">)</span></span>
97<span id="cb4-3"><a href="#cb4-3" aria-hidden="true"></a>fmt.Println(y)</span> 97<span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a>fmt<span class="op">.</span>Println<span class="op">(</span>y<span class="op">)</span></span>
98<span id="cb4-4"><a href="#cb4-4" aria-hidden="true"></a><span class="co">// results in a runtime error:</span></span> 98<span id="cb4-4"><a href="#cb4-4" aria-hidden="true" tabindex="-1"></a><span class="co">// results in a runtime error:</span></span>
99<span id="cb4-5"><a href="#cb4-5" aria-hidden="true"></a><span class="co">// panic: interface conversion: interface {} is int, not float64</span></span></code></pre></div> 99<span id="cb4-5"><a href="#cb4-5" aria-hidden="true" tabindex="-1"></a><span class="co">// panic: interface conversion: interface {} is int, not float64</span></span></code></pre></div>
100<h3 id="date-and-time">Date and Time</h3> 100<h3 id="date-and-time">Date and Time</h3>
101<p>Anyone that has written Go previously, will probably already know what I am getting at here. For the uninitiated, parsing and formatting dates in Go requires a “layout”. This “layout” is based on magical reference date:</p> 101<p>Anyone that has written Go previously, will probably already know what I am getting at here. For the uninitiated, parsing and formatting dates in Go requires a “layout”. This “layout” is based on magical reference date:</p>
102<pre><code>Mon Jan 2 15:04:05 MST 2006</code></pre> 102<pre><code>Mon Jan 2 15:04:05 MST 2006</code></pre>
103<p>Which is the date produced when you write the first seven natural numbers like so:</p> 103<p>Which is the date produced when you write the first seven natural numbers like so:</p>
104<pre><code>01/02 03:04:05 &#39;06 -0700</code></pre> 104<pre><code>01/02 03:04:05 &#39;06 -0700</code></pre>
105<p>Parsing a string in <code>YYYY-MM-DD</code> format would look something like:</p> 105<p>Parsing a string in <code>YYYY-MM-DD</code> format would look something like:</p>
106<div class="sourceCode" id="cb7"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true"></a><span class="kw">const</span> layout = <span class="st">&quot;2006-01-02&quot;</span></span> 106<div class="sourceCode" id="cb7"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="kw">const</span> layout <span class="op">=</span> <span class="st">&quot;2006-01-02&quot;</span></span>
107<span id="cb7-2"><a href="#cb7-2" aria-hidden="true"></a>time.Parse(layout, <span class="st">&quot;2020-08-01&quot;</span>)</span></code></pre></div> 107<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a>time<span class="op">.</span>Parse<span class="op">(</span>layout<span class="op">,</span> <span class="st">&quot;2020-08-01&quot;</span><span class="op">)</span></span></code></pre></div>
108<p>This so-called “intuitive” method of formatting dates doesn’t allow you to print <code>0000 hrs</code> as <code>2400 hrs</code>, it doesn’t allow you to omit the leading zero in 24 hour formats. It is rife with inconveniences, if only there were a <a href="https://man7.org/linux/man-pages/man3/strftime.3.html">tried and tested</a> date formatting convention …</p> 108<p>This so-called “intuitive” method of formatting dates doesn’t allow you to print <code>0000 hrs</code> as <code>2400 hrs</code>, it doesn’t allow you to omit the leading zero in 24 hour formats. It is rife with inconveniences, if only there were a <a href="https://man7.org/linux/man-pages/man3/strftime.3.html">tried and tested</a> date formatting convention …</p>
109<h3 id="statements-over-expressions">Statements over Expressions</h3> 109<h3 id="statements-over-expressions">Statements over Expressions</h3>
110<p>Statements have side effects, expressions return values. More often than not, expressions are easier to understand at a glance: evaluate the LHS and assign the same to the RHS.</p> 110<p>Statements have side effects, expressions return values. More often than not, expressions are easier to understand at a glance: evaluate the LHS and assign the same to the RHS.</p>
111<p>Rust allows you to create local namespaces, and treats blocks (<code>{}</code>) as expressions:</p> 111<p>Rust allows you to create local namespaces, and treats blocks (<code>{}</code>) as expressions:</p>
112<div class="sourceCode" id="cb8"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true"></a><span class="kw">let</span> twenty_seven <span class="op">=</span> <span class="op">{</span></span> 112<div class="sourceCode" id="cb8"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a><span class="kw">let</span> twenty_seven <span class="op">=</span> <span class="op">{</span></span>
113<span id="cb8-2"><a href="#cb8-2" aria-hidden="true"></a> <span class="kw">let</span> three <span class="op">=</span> <span class="dv">1</span> <span class="op">+</span> <span class="dv">2</span><span class="op">;</span></span> 113<span id="cb8-2"><a href="#cb8-2" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> three <span class="op">=</span> <span class="dv">1</span> <span class="op">+</span> <span class="dv">2</span><span class="op">;</span></span>
114<span id="cb8-3"><a href="#cb8-3" aria-hidden="true"></a> <span class="kw">let</span> nine <span class="op">=</span> three <span class="op">*</span> three<span class="op">;</span></span> 114<span id="cb8-3"><a href="#cb8-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> nine <span class="op">=</span> three <span class="op">*</span> three<span class="op">;</span></span>
115<span id="cb8-4"><a href="#cb8-4" aria-hidden="true"></a> nine <span class="op">*</span> three</span> 115<span id="cb8-4"><a href="#cb8-4" aria-hidden="true" tabindex="-1"></a> nine <span class="op">*</span> three</span>
116<span id="cb8-5"><a href="#cb8-5" aria-hidden="true"></a><span class="op">};</span></span></code></pre></div> 116<span id="cb8-5"><a href="#cb8-5" aria-hidden="true" tabindex="-1"></a><span class="op">};</span></span></code></pre></div>
117<p>The Go equivalent of the same:</p> 117<p>The Go equivalent of the same:</p>
118<div class="sourceCode" id="cb9"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true"></a>twenty_seven := <span class="ot">nil</span></span> 118<div class="sourceCode" id="cb9"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>twenty_seven <span class="op">:=</span> <span class="ot">nil</span></span>
119<span id="cb9-2"><a href="#cb9-2" aria-hidden="true"></a></span> 119<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a></span>
120<span id="cb9-3"><a href="#cb9-3" aria-hidden="true"></a>three := <span class="dv">1</span> + <span class="dv">2</span></span> 120<span id="cb9-3"><a href="#cb9-3" aria-hidden="true" tabindex="-1"></a>three <span class="op">:=</span> <span class="dv">1</span> <span class="op">+</span> <span class="dv">2</span></span>
121<span id="cb9-4"><a href="#cb9-4" aria-hidden="true"></a>nine := three * three</span> 121<span id="cb9-4"><a href="#cb9-4" aria-hidden="true" tabindex="-1"></a>nine <span class="op">:=</span> three <span class="op">*</span> three</span>
122<span id="cb9-5"><a href="#cb9-5" aria-hidden="true"></a>twenty_seven = nine * three</span></code></pre></div> 122<span id="cb9-5"><a href="#cb9-5" aria-hidden="true" tabindex="-1"></a>twenty_seven <span class="op">=</span> nine <span class="op">*</span> three</span></code></pre></div>
123<h3 id="erroring-out-on-unused-variables">Erroring out on unused variables</h3> 123<h3 id="erroring-out-on-unused-variables">Erroring out on unused variables</h3>
124<p>Want to quickly prototype something? Go says no! In all seriousness, a warning would suffice, I don’t want to have to go back and comment each unused import out, only to come back and uncomment them a few seconds later.</p> 124<p>Want to quickly prototype something? Go says no! In all seriousness, a warning would suffice, I don’t want to have to go back and comment each unused import out, only to come back and uncomment them a few seconds later.</p>
125<h3 id="error-handling">Error handling</h3> 125<h3 id="error-handling">Error handling</h3>
126<div class="sourceCode" id="cb10"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true"></a><span class="kw">if</span> err != <span class="ot">nil</span> { ... }</span></code></pre></div> 126<div class="sourceCode" id="cb10"><pre class="sourceCode go"><code class="sourceCode go"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="kw">if</span> err <span class="op">!=</span> <span class="ot">nil</span> <span class="op">{</span> <span class="op">...</span> <span class="op">}</span></span></code></pre></div>
127<p>Need I say more? I will, for good measure:</p> 127<p>Need I say more? I will, for good measure:</p>
128<ol type="1"> 128<ol type="1">
129<li>Error handling is optional</li> 129<li>Error handling is optional</li>
130<li>Errors are propagated via a clunky <code>if</code> + <code>return</code> statement</li> 130<li>Errors are propagated via a clunky <code>if</code> + <code>return</code> statement</li>
131</ol> 131</ol>
132<p>I prefer Haskell’s “Monadic” error handling, which is employed by Rust as well:</p> 132<p>I prefer Haskell’s “Monadic” error handling, which is employed by Rust as well:</p>
133<div class="sourceCode" id="cb11"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true"></a><span class="co">// 1. error handling is compulsory</span></span> 133<div class="sourceCode" id="cb11"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a><span class="co">// 1. error handling is compulsory</span></span>
134<span id="cb11-2"><a href="#cb11-2" aria-hidden="true"></a><span class="co">// 2. errors are propagated with the `?` operator</span></span> 134<span id="cb11-2"><a href="#cb11-2" aria-hidden="true" tabindex="-1"></a><span class="co">// 2. errors are propagated with the `?` operator</span></span>
135<span id="cb11-3"><a href="#cb11-3" aria-hidden="true"></a><span class="kw">fn</span> foo() <span class="op">-&gt;</span> <span class="dt">Result</span><span class="op">&lt;</span><span class="dt">String</span><span class="op">,</span> <span class="pp">io::</span><span class="bu">Error</span><span class="op">&gt;</span> <span class="op">{</span></span> 135<span id="cb11-3"><a href="#cb11-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> foo() <span class="op">-&gt;</span> <span class="dt">Result</span><span class="op">&lt;</span><span class="dt">String</span><span class="op">,</span> <span class="pp">io::</span><span class="bu">Error</span><span class="op">&gt;</span> <span class="op">{</span></span>
136<span id="cb11-4"><a href="#cb11-4" aria-hidden="true"></a> <span class="kw">let</span> <span class="kw">mut</span> f <span class="op">=</span> <span class="pp">File::</span>open(<span class="st">&quot;foo.txt&quot;</span>)<span class="op">?;</span> <span class="co">// return if error</span></span> 136<span id="cb11-4"><a href="#cb11-4" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> <span class="kw">mut</span> f <span class="op">=</span> <span class="pp">File::</span>open(<span class="st">&quot;foo.txt&quot;</span>)<span class="op">?;</span> <span class="co">// return if error</span></span>
137<span id="cb11-5"><a href="#cb11-5" aria-hidden="true"></a> <span class="kw">let</span> <span class="kw">mut</span> s <span class="op">=</span> <span class="dt">String</span><span class="pp">::</span>new()<span class="op">;</span></span> 137<span id="cb11-5"><a href="#cb11-5" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> <span class="kw">mut</span> s <span class="op">=</span> <span class="dt">String</span><span class="pp">::</span>new()<span class="op">;</span></span>
138<span id="cb11-6"><a href="#cb11-6" aria-hidden="true"></a></span> 138<span id="cb11-6"><a href="#cb11-6" aria-hidden="true" tabindex="-1"></a></span>
139<span id="cb11-7"><a href="#cb11-7" aria-hidden="true"></a> f<span class="op">.</span>read_to_string(<span class="op">&amp;</span><span class="kw">mut</span> s)<span class="op">?;</span> <span class="co">// return if error</span></span> 139<span id="cb11-7"><a href="#cb11-7" aria-hidden="true" tabindex="-1"></a> f<span class="op">.</span>read_to_string(<span class="op">&amp;</span><span class="kw">mut</span> s)<span class="op">?;</span> <span class="co">// return if error</span></span>
140<span id="cb11-8"><a href="#cb11-8" aria-hidden="true"></a></span> 140<span id="cb11-8"><a href="#cb11-8" aria-hidden="true" tabindex="-1"></a></span>
141<span id="cb11-9"><a href="#cb11-9" aria-hidden="true"></a> <span class="cn">Ok</span>(s) <span class="co">// all good, return a string inside a `Result` context</span></span> 141<span id="cb11-9"><a href="#cb11-9" aria-hidden="true" tabindex="-1"></a> <span class="cn">Ok</span>(s) <span class="co">// all good, return a string inside a `Result` context</span></span>
142<span id="cb11-10"><a href="#cb11-10" aria-hidden="true"></a><span class="op">}</span></span> 142<span id="cb11-10"><a href="#cb11-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
143<span id="cb11-11"><a href="#cb11-11" aria-hidden="true"></a></span> 143<span id="cb11-11"><a href="#cb11-11" aria-hidden="true" tabindex="-1"></a></span>
144<span id="cb11-12"><a href="#cb11-12" aria-hidden="true"></a><span class="kw">fn</span> main() <span class="op">{</span></span> 144<span id="cb11-12"><a href="#cb11-12" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> main() <span class="op">{</span></span>
145<span id="cb11-13"><a href="#cb11-13" aria-hidden="true"></a> <span class="co">// `contents` is an enum known as Result:</span></span> 145<span id="cb11-13"><a href="#cb11-13" aria-hidden="true" tabindex="-1"></a> <span class="co">// `contents` is an enum known as Result:</span></span>
146<span id="cb11-14"><a href="#cb11-14" aria-hidden="true"></a> <span class="kw">let</span> contents <span class="op">=</span> foo()<span class="op">;</span></span> 146<span id="cb11-14"><a href="#cb11-14" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> contents <span class="op">=</span> foo()<span class="op">;</span></span>
147<span id="cb11-15"><a href="#cb11-15" aria-hidden="true"></a> <span class="kw">match</span> contents <span class="op">{</span></span> 147<span id="cb11-15"><a href="#cb11-15" aria-hidden="true" tabindex="-1"></a> <span class="kw">match</span> contents <span class="op">{</span></span>
148<span id="cb11-16"><a href="#cb11-16" aria-hidden="true"></a> <span class="cn">Ok</span>(c) <span class="op">=&gt;</span> <span class="pp">println!</span>(c)<span class="op">,</span></span> 148<span id="cb11-16"><a href="#cb11-16" aria-hidden="true" tabindex="-1"></a> <span class="cn">Ok</span>(c) <span class="op">=&gt;</span> <span class="pp">println!</span>(c)<span class="op">,</span></span>
149<span id="cb11-17"><a href="#cb11-17" aria-hidden="true"></a> <span class="cn">Err</span>(e) <span class="op">=&gt;</span> <span class="pp">eprintln!</span>(e)</span> 149<span id="cb11-17"><a href="#cb11-17" aria-hidden="true" tabindex="-1"></a> <span class="cn">Err</span>(e) <span class="op">=&gt;</span> <span class="pp">eprintln!</span>(e)</span>
150<span id="cb11-18"><a href="#cb11-18" aria-hidden="true"></a> <span class="op">}</span></span> 150<span id="cb11-18"><a href="#cb11-18" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span>
151<span id="cb11-19"><a href="#cb11-19" aria-hidden="true"></a><span class="op">}</span></span></code></pre></div> 151<span id="cb11-19"><a href="#cb11-19" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
152<h3 id="conclusion">Conclusion</h3> 152<h3 id="conclusion">Conclusion</h3>
153<p>I did not want to conclude without talking about stylistic choices, lack of metaprogramming, bizzare export rules, but, I am too busy converting my <code>interface{}</code> types into actual generic code for Go v2.</p> 153<p>I did not want to conclude without talking about stylistic choices, lack of metaprogramming, bizzare export rules, but, I am too busy converting my <code>interface{}</code> types into actual generic code for Go v2.</p>
154 154
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