pattern-matching.md

Pattern Matching

Pattern matching is a powerful part of Elixir, it allows us to match simple values, data structures, and even functions. In this lesson we will begin to see how pattern matching is used.

Table of Contents

• Match operator
• Pin operator

Match operator

Are you ready for a curveball? In Elixir, the = operator is actually our match operator. Through the match operator we can assign and then match values, let's take a look:

iex> x = 1
1

Now let's try some simple matching:

iex> 1 = x
1
iex> 2 = x
** (MatchError) no match of right hand side value: 1

Let's try that with some of the collections we know:

# Lists
iex> list = [1, 2, 3]
iex> [1, 2, 3] = list
[1, 2, 3]
iex> [] = list
** (MatchError) no match of right hand side value: [1, 2, 3]

iex> [1|tail] = list
[1, 2, 3]
iex> tail
[2, 3]
iex> [2|_] = list
** (MatchError) no match of right hand side value: [1, 2, 3]

# Tuples
iex> {:ok, value} = {:ok, "Successful!"}
{:ok, "Successful!"}
iex> value
"Successful!"
iex> {:ok, value} = {:error}
** (MatchError) no match of right hand side value: {:error}

Pin operator

As we just learned, the match operator handles assignment when the left side of the match includes a variable. In some cases this behavior, variable rebinding, is undesirable. For these situations, we have the ^ operator:

This example comes directly from the official Elixir Getting Started guide.

iex> x = 1
1
iex> ^x = 2
** (MatchError) no match of right hand side value: 2
iex> {x, ^x} = {2, 1}
{2, 1}
iex> x
2