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141 lines
6.3 KiB
141 lines
6.3 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 - If Your Data Has a Schema, Use a Structure</h1> |
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<span class="post-date"> |
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2019-06-25 |
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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/data-classes/">#data classes</a> |
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<a href="https://blog.juliobiason.me/tags/structs/">#structs</a> |
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<p>You may be tempted to use a list (or tuple, if your language allows) to keep |
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your data if it has, say, only 2 fields. Don't.</p> |
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<span id="continue-reading"></span> |
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<p>Some languages allow unstructured data to be kept in the format of tuples: |
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They act like lists, but you can use to store heterogeneous data (which is a |
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cute way of "it stores fields of different types").</p> |
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<p>This languages also allow you to "destructurize" them, so you can extract |
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elements from them without directly accessing them by index.</p> |
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<p>For example, in Python, you can have a tuple with:</p> |
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span>a_tuple = ('</span><span style="color:#a3be8c;">A String</span><span>', </span><span style="color:#d08770;">1</span><span>, </span><span style="color:#d08770;">7.5</span><span>) |
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</span></code></pre> |
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<p>And you can destructure it with</p> |
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span>some_string, an_integer, a_float = a_tuple |
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</span></code></pre> |
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<p>See? It's simple! You don't need to create a whole structure if you're just |
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passing a string, an integer and a float around.</p> |
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<p>Except, you do need a structure 'cause your data has a <em>schema</em>.</p> |
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<p>Tuples and destructuring should be used only when you need to pass data from |
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one function to another -- and barely that. When you have this tuple being |
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passed around, being destructured and created again -- say, you are adding one |
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value of the tuple to another value and producing a new tuple in the same |
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format -- then you have a structured -- and <em>schemaed</em> data.</p> |
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<p>And when you have a structured data, you must use a data class or a struct (or |
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even |
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<a href="https://docs.python.org/3/library/collections.html?highlight=namedtuple#collections.namedtuple">NamedTuples</a>, |
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if you're using Python).</p> |
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<p>Although it may look way more simpler to keep destructuring and building the |
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tuple over and over, in the long run you'll end up with a mess: a simple |
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change -- like adding a new field -- will require checking every destructuring |
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and every creation of the tuple to make sure if will stay in the same shape |
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every time.</p> |
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<p>So: You data has a schema? Use a Data Class or Class or Struct. Only if it is |
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schemaless, then you can use a tuple.</p> |
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<p>I've seen this used at least once. At the very start of the project, it |
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may seem easier to just store the data as a tuple and destructure it and build |
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it again when needed. There was even a whole module designed to receiving |
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tuples, destructure them and rebuild new ones (for example, a function that |
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would receive two tuples and compute the sum of the "value" field of each, |
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building a new tuple as a result). But because of this design, to add just a |
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new field, I had to change 14 files and do 168 changes around -- 'cause there |
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was a function to add two tuples, but there were points where you need just |
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one field, and there wasn't a function for it.</p> |
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<p>It would be easier to use if there were functions to extract each field, and |
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add two tuples, and what else was needed for managing the tuples, but then you |
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have to ask yourself: Why not use a class for that?</p> |
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<div style="float:left"> |
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<< <a href="/books/things-i-learnt/data-types">Types Say What Your Data Is</a> |
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<div style="float:right"> |
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<a href="/books/things-i-learnt/outside-project">Don't Mess With Things Outside Your Project</a> >> |
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