Today I Learned

A Hashrocket project

Elixir Pattern Matching with Variables

Let’s say you have a variable that you want to pattern match.

By default Elixir won’t use the variable’s value to do the pattern matching and it will do a regular assignment, overriding the original variable’s value:

iex(1)> year = 2020
2020

iex(2)> car = %{year: 2019}
%{year: 2019}

iex(3)> %{year: year} = car
%{year: 2019}

iex(4)> year
2019

Elixir has the pin opertator ^ that does exactly what we need. So in our example we can use the pin operator and if it doesn’t match you get an error:

iex(1)> year = 2020
2020

iex(2)> car = %{year: 2019}
%{year: 2019}

iex(3)> %{year: ^year} = car
** (MatchError) no match of right hand side value: %{year: 2019}
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