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01/08 — 2020
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<h1>
Gripes With Go
</h1>
<div class="post-text">
<p>You’ve read a lot of posts about the shortcomings of the Go
programming language, so what’s one more.</p>
<ol type="1">
<li><a href="#lack-of-sum-types">Lack of sum types</a></li>
<li><a href="#type-assertions">Type assertions</a></li>
<li><a href="#date-and-time">Date and Time</a></li>
<li><a href="#statements-over-expressions">Statements over
Expressions</a></li>
<li><a href="#erroring-out-on-unused-variables">Erroring out on unused
variables</a></li>
<li><a href="#error-handling">Error handling</a></li>
</ol>
<h3 id="lack-of-sum-types">Lack of Sum types</h3>
<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>
<p>A type to represent gender for example:</p>
<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>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="kw">const</span> <span class="op">(</span></span>
<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>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a> Female <span class="co">// assigns Female to 1</span></span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a> Other <span class="co">// assigns Other to 2</span></span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a><span class="op">)</span></span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a></span>
<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">"My gender is "</span><span class="op">,</span> Male<span class="op">)</span></span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a><span class="co">// My gender is 0</span></span>
<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>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a></span>
<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>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a> <span class="cf">switch</span> <span class="op">(</span>g<span class="op">)</span> <span class="op">{</span></span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a> <span class="cf">case</span> <span class="dv">0</span><span class="op">:</span> <span class="cf">return</span> <span class="st">"Male"</span></span>
<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a> <span class="cf">case</span> <span class="dv">1</span><span class="op">:</span> <span class="cf">return</span> <span class="st">"Female"</span></span>
<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a> <span class="cf">default</span><span class="op">:</span> <span class="cf">return</span> <span class="st">"Other"</span></span>
<span id="cb1-18"><a href="#cb1-18" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span>
<span id="cb1-19"><a href="#cb1-19" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
<span id="cb1-20"><a href="#cb1-20" aria-hidden="true" tabindex="-1"></a></span>
<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>
<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>
<p>The Haskell equivalent of the same:</p>
<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>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a> <span class="op">|</span> <span class="dt">Female</span></span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a> <span class="op">|</span> <span class="dt">Other</span></span>
<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>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a></span>
<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">"My gender is "</span> <span class="op">++</span> (<span class="fu">show</span> <span class="dt">Male</span>)</span></code></pre></div>
<h3 id="type-assertions">Type Assertions</h3>
<p>A downcast with an optional error check? What could go wrong?</p>
<p>Type assertions in Go allow you to do:</p>
<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>
<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>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> goodToGo <span class="op">{</span></span>
<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>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<p>The error check however is optional:</p>
<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>
<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>
<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>
<span id="cb4-4"><a href="#cb4-4" aria-hidden="true" tabindex="-1"></a><span class="co">// results in a runtime error:</span></span>
<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>
<h3 id="date-and-time">Date and Time</h3>
<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>
<pre><code>Mon Jan 2 15:04:05 MST 2006</code></pre>
<p>Which is the date produced when you write the first seven natural
numbers like so:</p>
<pre><code>01/02 03:04:05 '06 -0700</code></pre>
<p>Parsing a string in <code>YYYY-MM-DD</code> format would look
something like:</p>
<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">"2006-01-02"</span></span>
<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">"2020-08-01"</span><span class="op">)</span></span></code></pre></div>
<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>
<h3 id="statements-over-expressions">Statements over Expressions</h3>
<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>
<p>Rust allows you to create local namespaces, and treats blocks
(<code>{}</code>) as expressions:</p>
<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>
<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>
<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>
<span id="cb8-4"><a href="#cb8-4" aria-hidden="true" tabindex="-1"></a> nine <span class="op">*</span> three</span>
<span id="cb8-5"><a href="#cb8-5" aria-hidden="true" tabindex="-1"></a><span class="op">};</span></span></code></pre></div>
<p>The Go equivalent of the same:</p>
<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>
<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a></span>
<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>
<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>
<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>
<h3 id="erroring-out-on-unused-variables">Erroring out on unused
variables</h3>
<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>
<h3 id="error-handling">Error handling</h3>
<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="cf">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>
<p>Need I say more? I will, for good measure:</p>
<ol type="1">
<li>Error handling is optional</li>
<li>Errors are propagated via a clunky <code>if</code> +
<code>return</code> statement</li>
</ol>
<p>I prefer Haskell’s “Monadic” error handling, which is employed by
Rust as well:</p>
<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>
<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>
<span id="cb11-3"><a href="#cb11-3" aria-hidden="true" tabindex="-1"></a><span class="kw">fn</span> foo() <span class="op">-></span> <span class="dt">Result</span><span class="op"><</span><span class="dt">String</span><span class="op">,</span> <span class="pp">io::</span><span class="bu">Error</span><span class="op">></span> <span class="op">{</span></span>
<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">"foo.txt"</span>)<span class="op">?;</span> <span class="co">// return if error</span></span>
<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>
<span id="cb11-6"><a href="#cb11-6" aria-hidden="true" tabindex="-1"></a></span>
<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">&</span><span class="kw">mut</span> s)<span class="op">?;</span> <span class="co">// return if error</span></span>
<span id="cb11-8"><a href="#cb11-8" aria-hidden="true" tabindex="-1"></a></span>
<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>
<span id="cb11-10"><a href="#cb11-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
<span id="cb11-11"><a href="#cb11-11" aria-hidden="true" tabindex="-1"></a></span>
<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>
<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>
<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>
<span id="cb11-15"><a href="#cb11-15" aria-hidden="true" tabindex="-1"></a> <span class="cf">match</span> contents <span class="op">{</span></span>
<span id="cb11-16"><a href="#cb11-16" aria-hidden="true" tabindex="-1"></a> <span class="cn">Ok</span>(c) <span class="op">=></span> <span class="pp">println!</span>(c)<span class="op">,</span></span>
<span id="cb11-17"><a href="#cb11-17" aria-hidden="true" tabindex="-1"></a> <span class="cn">Err</span>(e) <span class="op">=></span> <span class="pp">eprintln!</span>(e)</span>
<span id="cb11-18"><a href="#cb11-18" aria-hidden="true" tabindex="-1"></a> <span class="op">}</span></span>
<span id="cb11-19"><a href="#cb11-19" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<h3 id="conclusion">Conclusion</h3>
<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>
</div>
<div class="intro">
Hi.
<div class="hot-links">
<a href="https://peppe.rs/index.xml" class="feed-button">Subscribe</a>
</div>
<p>I'm Akshay, programmer and pixel-artist.</p>
<p>
I write <a href="https://git.peppe.rs">open-source stuff</a> to pass time.
I also design fonts:
<a href="https://git.peppe.rs/fonts/scientifica/about">scientifica</a>,
<a href="https://git.peppe.rs/fonts/curie/about">curie</a>.
</p>
<p>Send me a mail at [email protected] or a message at [email protected].</p>
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