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118 lines
4.5 KiB
118 lines
4.5 KiB
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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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<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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<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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<< <a href="/books/things-i-learnt/document-it">Documentation Is a Love Letter To Your Future Self</a> |
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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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