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12 | <language>en-us</language> | 12 | <language>en-us</language> |
13 | <copyright>Creative Commons BY-NC-SA 4.0</copyright> | 13 | <copyright>Creative Commons BY-NC-SA 4.0</copyright> |
14 | <item> | 14 | <item> |
15 | <title>Gripes With Go</title> | ||
16 | <description><p>You’ve read a lot of posts about the shortcomings of the Go programming language, so what’s one more.</p> | ||
17 | <ol type="1"> | ||
18 | <li><a href="#lack-of-sum-types">Lack of sum types</a></li> | ||
19 | <li><a href="#type-assertions">Type assertions</a></li> | ||
20 | <li><a href="#date-and-time">Date and Time</a></li> | ||
21 | <li><a href="#statements-over-expressions">Statements over Expressions</a></li> | ||
22 | <li><a href="#erroring-out-on-unused-variables">Erroring out on unused variables</a></li> | ||
23 | <li><a href="#error-handling">Error handling</a></li> | ||
24 | </ol> | ||
25 | <h3 id="lack-of-sum-types">Lack of Sum types</h3> | ||
26 | <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> | ||
27 | <p>A type to represent gender for example:</p> | ||
28 | <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> | ||
29 | <span id="cb1-2"><a href="#cb1-2" aria-hidden="true"></a></span> | ||
30 | <span id="cb1-3"><a href="#cb1-3" aria-hidden="true"></a><span class="kw">const</span> (</span> | ||
31 | <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> | ||
32 | <span id="cb1-5"><a href="#cb1-5" aria-hidden="true"></a> Female <span class="co">// assigns Female to 1</span></span> | ||
33 | <span id="cb1-6"><a href="#cb1-6" aria-hidden="true"></a> Other <span class="co">// assigns Other to 2</span></span> | ||
34 | <span id="cb1-7"><a href="#cb1-7" aria-hidden="true"></a>)</span> | ||
35 | <span id="cb1-8"><a href="#cb1-8" aria-hidden="true"></a></span> | ||
36 | <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> | ||
37 | <span id="cb1-10"><a href="#cb1-10" aria-hidden="true"></a><span class="co">// My gender is 0</span></span> | ||
38 | <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> | ||
39 | <span id="cb1-12"><a href="#cb1-12" aria-hidden="true"></a></span> | ||
40 | <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> | ||
41 | <span id="cb1-14"><a href="#cb1-14" aria-hidden="true"></a> <span class="kw">switch</span> (g) {</span> | ||
42 | <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> | ||
43 | <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> | ||
44 | <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> | ||
45 | <span id="cb1-18"><a href="#cb1-18" aria-hidden="true"></a> }</span> | ||
46 | <span id="cb1-19"><a href="#cb1-19" aria-hidden="true"></a>}</span> | ||
47 | <span id="cb1-20"><a href="#cb1-20" aria-hidden="true"></a></span> | ||
48 | <span id="cb1-21"><a href="#cb1-21" aria-hidden="true"></a><span class="co">// You can accidentally do stupid stuff like:</span></span> | ||
49 | <span id="cb1-22"><a href="#cb1-22" aria-hidden="true"></a>gender := Male + <span class="dv">1</span></span></code></pre></div> | ||
50 | <p>The Haskell equivalent of the same:</p> | ||
51 | <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> | ||
52 | <span id="cb2-2"><a href="#cb2-2" aria-hidden="true"></a> <span class="op">|</span> <span class="dt">Female</span></span> | ||
53 | <span id="cb2-3"><a href="#cb2-3" aria-hidden="true"></a> <span class="op">|</span> <span class="dt">Other</span></span> | ||
54 | <span id="cb2-4"><a href="#cb2-4" aria-hidden="true"></a> <span class="kw">deriving</span> (<span class="dt">Show</span>)</span> | ||
55 | <span id="cb2-5"><a href="#cb2-5" aria-hidden="true"></a></span> | ||
56 | <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> | ||
57 | <h3 id="type-assertions">Type Assertions</h3> | ||
58 | <p>A downcast with an optional error check? What could go wrong?</p> | ||
59 | <p>Type assertions in Go allow you to do:</p> | ||
60 | <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> | ||
61 | <span id="cb3-2"><a href="#cb3-2" aria-hidden="true"></a>y, goodToGo := x.(<span class="dt">int</span>)</span> | ||
62 | <span id="cb3-3"><a href="#cb3-3" aria-hidden="true"></a><span class="kw">if</span> goodToGo {</span> | ||
63 | <span id="cb3-4"><a href="#cb3-4" aria-hidden="true"></a> fmt.Println(y)</span> | ||
64 | <span id="cb3-5"><a href="#cb3-5" aria-hidden="true"></a>}</span></code></pre></div> | ||
65 | <p>The error check however is optional:</p> | ||
66 | <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> | ||
67 | <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> | ||
68 | <span id="cb4-3"><a href="#cb4-3" aria-hidden="true"></a>fmt.Println(y)</span> | ||
69 | <span id="cb4-4"><a href="#cb4-4" aria-hidden="true"></a><span class="co">// results in a runtime error:</span></span> | ||
70 | <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> | ||
71 | <h3 id="date-and-time">Date and Time</h3> | ||
72 | <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> | ||
73 | <pre><code>Mon Jan 2 15:04:05 MST 2006</code></pre> | ||
74 | <p>Which is the date produced when you write the first seven natural numbers like so:</p> | ||
75 | <pre><code>01/02 03:04:05 &#39;06 -0700</code></pre> | ||
76 | <p>Parsing a string in <code>YYYY-MM-DD</code> format would look something like:</p> | ||
77 | <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> | ||
78 | <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> | ||
79 | <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> | ||
80 | <h3 id="statements-over-expressions">Statements over Expressions</h3> | ||
81 | <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> | ||
82 | <p>Rust allows you to create local namespaces, and treats blocks (<code>{}</code>) as expressions:</p> | ||
83 | <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> | ||
84 | <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> | ||
85 | <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> | ||
86 | <span id="cb8-4"><a href="#cb8-4" aria-hidden="true"></a> nine <span class="op">*</span> three</span> | ||
87 | <span id="cb8-5"><a href="#cb8-5" aria-hidden="true"></a><span class="op">};</span></span></code></pre></div> | ||
88 | <p>The Go equivalent of the same:</p> | ||
89 | <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> | ||
90 | <span id="cb9-2"><a href="#cb9-2" aria-hidden="true"></a></span> | ||
91 | <span id="cb9-3"><a href="#cb9-3" aria-hidden="true"></a>three := <span class="dv">1</span> + <span class="dv">2</span></span> | ||
92 | <span id="cb9-4"><a href="#cb9-4" aria-hidden="true"></a>nine := three * three</span> | ||
93 | <span id="cb9-5"><a href="#cb9-5" aria-hidden="true"></a>twenty_seven = nine * three</span></code></pre></div> | ||
94 | <h3 id="erroring-out-on-unused-variables">Erroring out on unused variables</h3> | ||
95 | <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> | ||
96 | <h3 id="error-handling">Error handling</h3> | ||
97 | <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> | ||
98 | <p>Need I say more? I will, for good measure:</p> | ||
99 | <ol type="1"> | ||
100 | <li>Error handling is optional</li> | ||
101 | <li>Errors are propagated via a clunky <code>if</code> + <code>return</code> statement</li> | ||
102 | </ol> | ||
103 | <p>I prefer Haskell’s “Monadic” error handling, which is employed by Rust as well:</p> | ||
104 | <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> | ||
105 | <span id="cb11-2"><a href="#cb11-2" aria-hidden="true"></a><span class="co">// 2. errors are propagated with the `?` operator</span></span> | ||
106 | <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> | ||
107 | <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> | ||
108 | <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> | ||
109 | <span id="cb11-6"><a href="#cb11-6" aria-hidden="true"></a></span> | ||
110 | <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> | ||
111 | <span id="cb11-8"><a href="#cb11-8" aria-hidden="true"></a></span> | ||
112 | <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> | ||
113 | <span id="cb11-10"><a href="#cb11-10" aria-hidden="true"></a><span class="op">}</span></span> | ||
114 | <span id="cb11-11"><a href="#cb11-11" aria-hidden="true"></a></span> | ||
115 | <span id="cb11-12"><a href="#cb11-12" aria-hidden="true"></a><span class="kw">fn</span> main() <span class="op">{</span></span> | ||
116 | <span id="cb11-13"><a href="#cb11-13" aria-hidden="true"></a> <span class="co">// `contents` is an enum known as Result:</span></span> | ||
117 | <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> | ||
118 | <span id="cb11-15"><a href="#cb11-15" aria-hidden="true"></a> <span class="kw">match</span> contents <span class="op">{</span></span> | ||
119 | <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> | ||
120 | <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> | ||
121 | <span id="cb11-18"><a href="#cb11-18" aria-hidden="true"></a> <span class="op">}</span></span> | ||
122 | <span id="cb11-19"><a href="#cb11-19" aria-hidden="true"></a><span class="op">}</span></span></code></pre></div> | ||
123 | <h3 id="conclusion">Conclusion</h3> | ||
124 | <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></description> | ||
125 | <link>https://peppe.rs/posts/gripes_with_go/</link> | ||
126 | <pubDate>Sat, 01 Aug 2020 11:55:00 +0000</pubDate> | ||
127 | <guid>https://peppe.rs/posts/gripes_with_go/</guid> | ||
128 | </item> | ||
129 | <item> | ||
15 | <title>Turing Complete Type Systems</title> | 130 | <title>Turing Complete Type Systems</title> |
16 | <description><p>Rust’s type system is Turing complete:</p> | 131 | <description><p>Rust’s type system is Turing complete:</p> |
17 | <ul> | 132 | <ul> |