https://duan.ca/tag/oop/ <p>Python's standard library includes a very handy <code>defaultdict</code>. It behaves almost exactly like the standard dictionary except it'll supply a pre-defined value for any non-existence keys. It is, unsurpringly, a subclass of <code>dict</code>.</p> <p>I find my self missing this handy container in Swift. Especially when I use a normal <code>Dictionary</code> to accumulate/coalesce values under distinct keys. So I wrote my own:</p> <script src="https://gist.github.com/dduan/31ed39c4c98ecb88290f0743cb394c20.js"></script> <p>There are a few noticable things about this implementation:</p> <ul> <li>It does not conform to the <code>DictionaryLiteralConvertible</code> protocol, for no good reasons, really. The initializer in this protocol takes a varadic argument. There's no conevient way to forward this array to a normal dictionary's initializer (incidentally, this is a Swift feature I really want). Plus, I don't need <code>DefaultDictionary</code> to be a literal convertible.</li> <li>Most of the code, including the imaginary <code>init</code> mentioned in previous point, simply reuses stuff from <code>Dictionary</code>: asscociated type, indexes, generator, subscript, etc.</li> </ul> <p>In comparison, Python implements <code>defaultdict</code> in a more intuitive way -- via inheritance.</p> <p>But do we want inheritance for <code>struct</code>s and <code>enum</code>s in Swift? What does that even mean? Is it simply a case that will go away when protocols become more powerful?</p> Thu, 19 May 2016 12:03:02 -0700 https://duan.ca/2016/05/19/a-case-for-oop/ https://duan.ca/2016/05/19/a-case-for-oop/