Pattern Matching Basics

Let's dive right in.

Rethink Assignment

In programming, you typically assign a variable with an = sign. In math, = means something else entirely. It means the two terms on either side of the sign are equivalent. That's the way it is with Elixir.

When Elixir sees an = it will try to make both sides equivalent. When you call a function, Elixir will do the same thing with the arguments you pass: pattern matching against the function's argument list.

You've already seen a little of this in the previous chapters. Let's take a look at a few more examples (feel free to open up iex and type these examples in):

<span class="hljs-comment">#a simple assignment</span>
pattern = <span class="hljs-string">&quot;match&quot;</span>

<span class="hljs-string">&quot;pat&quot;</span> &lt;&gt; tern = <span class="hljs-string">&quot;pattern match&quot;</span>
<span class="hljs-comment">#a little weirder, the variable &#x27;tern&#x27; = &quot;tern match&quot;</span>

[<span class="hljs-number">1</span>, x, <span class="hljs-number">5</span>] = [<span class="hljs-number">1</span>, <span class="hljs-number">10</span>, <span class="hljs-number">5</span>]
<span class="hljs-comment">#something straightforward: x = 10</span>

This is, in a sense, destructuring assignment that you would see in JavaScript, Ruby, ES6:

<span class="hljs-keyword">var</span> [x, y, z] = [<span class="hljs-number">1</span>,<span class="hljs-number">2</span>,<span class="hljs-number">3</span>];

But Pattern Matching is a whole lot more than this. While you can indeed use it to assign values, it's much more useful when used with function calls.