https://nalar.dev/tags/software-design/ Recent content in Software Design on Nalar Hugo en-us Tue, 01 Sep 2026 00:00:00 +0700 https://nalar.dev/design-value-objects-with-python-dataclasses/ Tue, 01 Sep 2026 00:00:00 +0700 https://nalar.dev/design-value-objects-with-python-dataclasses/ <p>Python dictionaries are convenient for passing a few values around, but they become fragile when a value has invariants or behavior that deserves a name. <code>dataclasses</code> can express small domain value objects without repetitive constructors and representation methods.</p> <h2 id="start-with-domain-meaning">Start with domain meaning</h2> <p>A price represented as a dictionary is easy to misuse:</p> <div x-data="{ code: $el.querySelector('code').innerText }" class="relative my-4 rounded-lg group" > <button @click="navigator.clipboard.writeText(code); $el.innerText = 'Copied!'; setTimeout(() => $el.innerText = 'Copy', 2000)" class="absolute top-2 right-2 bg-neutral-700 text-white text-xs px-2 py-1 rounded opacity-0 group-hover:opacity-100 transition-opacity" > Copy </button> <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-python" data-lang="python"><span style="display:flex;"><span>price <span style="color:#f92672">=</span> {<span style="color:#e6db74">&#34;amount&#34;</span>: <span style="color:#ae81ff">1299</span>, <span style="color:#e6db74">&#34;currency&#34;</span>: <span style="color:#e6db74">&#34;USD&#34;</span>}</span></span></code></pre></div> </div> <p>Any caller can omit a key or accidentally mix cents and dollars. A value object makes the contract explicit:</p> https://nalar.dev/python-protocols-and-structural-subtyping/ Tue, 01 Sep 2026 00:00:00 +0700 https://nalar.dev/python-protocols-and-structural-subtyping/ <p>Python code often depends on behavior rather than a specific class hierarchy. A function may only need an object with a <code>send()</code> method, a <code>read()</code> method, or a pair of repository operations.</p> <p><code>typing.Protocol</code> lets type checkers describe those behavioral requirements directly. A class satisfies a protocol by having compatible members; it does not need to inherit from the protocol.</p> <p>This is structural subtyping: &ldquo;if it has the required shape, it can be used here.&rdquo;</p>