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119 lines
4.5 KiB
119 lines
4.5 KiB
11 months ago
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<!DOCTYPE html>
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<html lang="en">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta http-equiv="content-type" content="text/html; charset=utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1, viewport-fit=cover">
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<title>Julio Biason .Me 4.3</title>
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<!-- CSS -->
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<link rel="stylesheet" href="https://blog.juliobiason.me/print.css" media="print">
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</head>
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<body class=" ">
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<div class="sidebar">
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<div class="container sidebar-sticky">
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<div class="sidebar-about">
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<a href="https://blog.juliobiason.me"><h1>Julio Biason .Me 4.3</h1></a>
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<p class="lead">Old school dev living in a 2.0 dev world</p>
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</div>
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<ul class="sidebar-nav">
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<li class="sidebar-nav-item"><a href="/">English</a></li>
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<li class="sidebar-nav-item"><a href="/pt">Português</a></li>
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<li class="sidebar-nav-item"><a href="/tags">Tags (EN)</a></li>
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<li class="sidebar-nav-item"><a href="/pt/tags">Tags (PT)</a></li>
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</ul>
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<div class="content container">
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<div class="post">
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<h1 class="post-title">Things I Learnt The Hard Way - The Function Documentation Is Its Contract</h1>
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<span class="post-date">
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2019-06-21
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<a href="https://blog.juliobiason.me/tags/books/">#books</a>
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<a href="https://blog.juliobiason.me/tags/things-i-learnt/">#things i learnt</a>
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<a href="https://blog.juliobiason.me/tags/documentation/">#documentation</a>
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<a href="https://blog.juliobiason.me/tags/contracts/">#contracts</a>
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</span>
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<p>When you start the code by <a href="/books/things-i-learnt/steps-as-comments">writing the general flow as
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steps</a> and making each step a
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function, you're actually making a contract (probably with your future self):
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I'm saying this function does <em>this</em> and <em>this</em> is what it does.</p>
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<span id="continue-reading"></span>
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<p>Remember that the documentation must be a clear explanation of what your code
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<em>is</em> doing and <em>why</em> it exists; remember that good messages will make <a href="/books/things-i-learnt/document-id">reading
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the code only by the function documentation</a>
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should be clear.</p>
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<p>A function called <code>mult</code>, documented as "Get the value and multiply by 2" but,
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when you look at the code, it does multiply by 2, but also sends the result
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through the network or even just asks a remote service to multiply the
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incoming result by 2, is clearly breaking its contract. It's not just
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multiplying by 2, it's doing more than just that, or it's asking someone else
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to manipulate the value.</p>
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<p>Now, what happens when this kind of thing happens?</p>
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<p>The easy solution is to change the documentation. But do you know if people
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who called the function expecting it to be "multiply value by 2" will be happy
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for it to call an external service? There is a clear breach of "contract" --
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whatever you initially said your function would do -- so the correct solution
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would be to add a new function with a proper contract -- and probably a better
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name.</p>
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<div>
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<div style="float:left">
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<< <a href="/books/things-i-learnt/document-it">Documentation Is a Love Letter To Your Future Self</a>
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</div>
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<div style="float:right">
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<a href="/books/things-i-learnt/document-and">If A Function Description Includes An And, It's Wrong</a> >>
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</div>
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</div>
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</div>
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</body>
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</html>
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