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<!doctype html><html lang=en><head><title>Item Patterns And Struct Else :: nilstriebs blog</title>
<meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=description content="Bringing more expressiveness to our items"><meta name=keywords content="design"><meta name=robots content="noodp"><link rel=canonical href=/posts/item-patterns-and-struct-else/><link rel=stylesheet href=/assets/style.css><link rel=apple-touch-icon href=/img/apple-touch-icon-192x192.png><link rel="shortcut icon" href=/img/favicon/orange.png><meta name=twitter:card content="summary"><meta property="og:locale" content="en"><meta property="og:type" content="article"><meta property="og:title" content="Item Patterns And Struct Else"><meta property="og:description" content="Bringing more expressiveness to our items"><meta property="og:url" content="/posts/item-patterns-and-struct-else/"><meta property="og:site_name" content="nilstriebs blog"><meta property="og:image" content="/img/favicon/orange.png"><meta property="og:image:width" content="2048"><meta property="og:image:height" content="1024"><meta property="article:published_time" content="2023-03-17 00:00:00 +0000 UTC"></head><body class=orange><div class="container center headings--one-size"><header class=header><div class=header__inner><div class=header__logo><a href=/><div class=logo>nilstriebs blog</div></a></div></div></header><div class=content><div class=post><h1 class=post-title><a href=/posts/item-patterns-and-struct-else/>Item Patterns And Struct Else</a></h1><div class=post-meta><span class=post-date>2023-03-17
</span><span class=post-author>:: Nilstrieb</span>
<!doctype html><html lang=en><head><title>Item Patterns And Struct Else :: Noratrieb's blog</title>
<meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=description content="Bringing more expressiveness to our items"><meta name=keywords content="design"><meta name=robots content="noodp"><link rel=canonical href=/posts/item-patterns-and-struct-else/><link rel=stylesheet href=/assets/style.css><link rel=apple-touch-icon href=/img/apple-touch-icon-192x192.png><link rel="shortcut icon" href=/img/favicon/orange.png><meta name=twitter:card content="summary"><meta property="og:locale" content="en"><meta property="og:type" content="article"><meta property="og:title" content="Item Patterns And Struct Else"><meta property="og:description" content="Bringing more expressiveness to our items"><meta property="og:url" content="/posts/item-patterns-and-struct-else/"><meta property="og:site_name" content="Noratrieb's blog"><meta property="og:image" content="/img/favicon/orange.png"><meta property="og:image:width" content="2048"><meta property="og:image:height" content="1024"><meta property="article:published_time" content="2023-03-17 00:00:00 +0000 UTC"></head><body class=orange><div class="container center headings--one-size"><header class=header><div class=header__inner><div class=header__logo><a href=/><div class=logo>noratrieb's blog</div></a></div></div></header><div class=content><div class=post><h1 class=post-title><a href=/posts/item-patterns-and-struct-else/>Item Patterns And Struct Else</a></h1><div class=post-meta><span class=post-date>2023-03-17
</span><span class=post-author>:: Noratrieb</span>
<span class=post-reading-time>:: 7 min read (1351 words)</span></div><span class=post-tags>#<a href=/tags/rust/>rust</a>&nbsp;
#<a href=/tags/language-design/>language-design</a>&nbsp;</span><div class=post-content><div><h1 id=pattern-matching>Pattern matching<a href=#pattern-matching class=hanchor arialabel=Anchor>&#8983;</a></h1><p>One of my favourite features of Rust is pattern matching. It&rsquo;s a simple and elegant way to deal with not just structs, but also enums!</p><div class=highlight><pre tabindex=0 style=color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-rust data-lang=rust><span style=display:flex><span><span style=color:#66d9ef>enum</span> <span style=color:#a6e22e>ItemKind</span> {
</span></span><span style=display:flex><span> Struct(String, Vec<span style=color:#f92672>&lt;</span>Field<span style=color:#f92672>&gt;</span>),
@ -45,7 +45,7 @@ Hashing something incorrectly <a href=https://github.com/rust-lang/rust/issues/8
</span></span><span style=display:flex><span>}
</span></span></code></pre></div><p>And with this, adding the visibility will cause a compiler error and alert us that we need to handle it in hashing.
(The decision whether we actually do want to handle it is still up to us. We could also just turn off the computer and make new friends outside.)</p><p>We can conclude that pattern matching is a great feature.</p><h1 id=limitations-of-pattern-matching>Limitations of pattern matching<a href=#limitations-of-pattern-matching class=hanchor arialabel=Anchor>&#8983;</a></h1><p>But there is one big limitation of pattern matching - all of its occurrences (<code>match</code>, <code>if let</code>, <code>if let</code> chains, <code>while let</code>, <code>while let</code> chains, <code>for</code>, <code>let</code>, <code>let else</code>, and function parameters
(we do have a lot of pattern matching)) are inside of bodies, mostly as part of expressions or statements.</p><p>This doesn&rsquo;t sound too bad. This is where the executed code resides. But it comes at a cost of consistency. We often add many syntactical niceties to expressions and statements, but forget about items.</p><h1 id=items-and-sadness>Items and sadness<a href=#items-and-sadness class=hanchor arialabel=Anchor>&#8983;</a></h1><p>Items have a hard life. They are the parents of everything important. <code>struct</code>, <code>enum</code>, <code>const</code>, <code>mod</code>, <code>fn</code>, <code>union</code>, <code>global_asm</code> are all things we use daily, yet their grammar is very limited. (&ldquo;free the items&rdquo; was an alternative blog post title, although &ldquo;freeing&rdquo; generally remains a concern of <a href=https://nilstrieb.github.io/nilstrieb-c-style-guide-edition-2/>my C style guide</a>).</p><p>For example, see the following code where we declare a few constants.</p><pre tabindex=0><code>const ONE: u8 = 1;
(we do have a lot of pattern matching)) are inside of bodies, mostly as part of expressions or statements.</p><p>This doesn&rsquo;t sound too bad. This is where the executed code resides. But it comes at a cost of consistency. We often add many syntactical niceties to expressions and statements, but forget about items.</p><h1 id=items-and-sadness>Items and sadness<a href=#items-and-sadness class=hanchor arialabel=Anchor>&#8983;</a></h1><p>Items have a hard life. They are the parents of everything important. <code>struct</code>, <code>enum</code>, <code>const</code>, <code>mod</code>, <code>fn</code>, <code>union</code>, <code>global_asm</code> are all things we use daily, yet their grammar is very limited. (&ldquo;free the items&rdquo; was an alternative blog post title, although &ldquo;freeing&rdquo; generally remains a concern of <a href=https://noratrieb.github.io/nilstrieb-c-style-guide-edition-2/>my C style guide</a>).</p><p>For example, see the following code where we declare a few constants.</p><pre tabindex=0><code>const ONE: u8 = 1;
const TWO: u8 = 1;
const THREE: u8 = 3;
</code></pre><p>There is nothing obviously wrong with this code. You understand it, I understand it, an ALGOL 68 developer from 1970 would probably understand it