Best Elixir Programming Books to Buy in September 2025
Learn Functional Programming with Elixir: New Foundations for a New World (The Pragmatic Programmers)
Elixir in Action, Third Edition
Programming Elixir ≥ 1.6: Functional |> Concurrent |> Pragmatic |> Fun
Elixir Patterns: The essential BEAM handbook for the busy developer
Elixir Programming Mastery: An In-Depth Exploration for Developers
The Art of Elixir: elegant, functional programming
Engineering Elixir Applications: Navigate Each Stage of Software Delivery with Confidence
Designing Elixir Systems With OTP: Write Highly Scalable, Self-healing Software with Layers
To define new guards in Elixir, you can use the defguard macro in a module. This allows you to create custom guards that can be used in pattern matching or guards in functions. Guards are expressions that can be used to filter out function clauses based on conditions.
When defining a new guard, you can specify the guard name along with the conditions that need to be met. For example, you could define a guard called is_even that checks if a number is even by using the % operator to check if the remainder is zero when dividing by 2.
Once you have defined your guard, you can use it in pattern matching or guards in functions just like you would with built-in guards such as is_integer or is_atom. This allows you to create more expressive and readable code by encapsulating complex conditions in custom guards.
Overall, defining new guards in Elixir can help you modularize your code and make it easier to understand and maintain.
How to combine multiple guards in Elixir?
To combine multiple guards in Elixir, you can use the and or or operators.
For example, to have a function with multiple guards using and, you can do the following:
def my_function(argument) when is_integer(argument) and argument > 0 do IO.puts "Argument is a positive integer" end
And to have a function with multiple guards using or, you can do the following:
def my_function(argument) when is_binary(argument) or is_list(argument) do IO.puts "Argument is a binary or a list" end
You can combine multiple guards using these operators as needed to create more complex guard clauses for your functions.
How to define guards for structs in Elixir?
In Elixir, guards are used to restrict the values that can be bound to variables. To define guards for structs, you can use pattern matching combined with guards in function clauses.
Here is an example of defining a guard for a struct in Elixir:
defmodule User do defstruct name: nil, age: nil
def is_adult(%User{age: age}) when age >= 18 do true end
def is_adult(_), do: false end
user = %User{name: "Alice", age: 25}
User.is_adult(user) # true
In this example, we define a User struct with two fields name and age. We then define a function is_adult/1 that takes a %User{} struct as an argument and checks if the age field is greater than or equal to 18 using a guard clause. If the condition is met, the function returns true, otherwise it returns false.
You can use guards with patterns to define more complex constraints for your structs in Elixir. It is important to note that guards are limited in their capabilities and should be used for simple checks only.
How to test guards in Elixir with ExUnit?
To test guards in Elixir with ExUnit, you can use the assert_match function to check if a specific error message is raised when a guard fails. Here's an example of how you can write a test for a function that uses guards:
defmodule ExampleTest do use ExUnit.Case
defmodule Example do defmodule Error do defexception message: "GuardError" end
def some\_function(arg) when is\_integer(arg) do
arg \* 2
end
def some\_function(\_) do
raise Error
end
end
test "should raise error for non-integer argument" do assert_raise Example.Error, fn -> Example.some_function("not_an_integer") end end end
In this test, we're asserting that calling Example.some_function("not_an_integer") will raise an error with the message "GuardError" when a non-integer argument is passed to the function. This way, you can test that the guard is working as expected.
How to override built-in guards in Elixir?
Unfortunately, it is not possible to directly override built-in guards in Elixir. Guards are a restricted subset of Elixir's syntax that are evaluated at compile-time and are used to constrain pattern matching and conditional clauses.
If you need custom behavior that cannot be achieved with the existing guards, you can use regular conditional expressions (if and case) within a function definition to achieve the desired behavior. You can also define your own custom guards using macros or functions.
For example, instead of using a built-in guard like is_integer/1, you can define a custom guard function like my_is_integer/1 that implements the desired behavior.
defmodule MyGuard do def my_is_integer(value) when is_integer(value) do true end
def my_is_integer(_), do: false end
defmodule MyModule do import MyGuard
def my_function(value) when my_is_integer(value) do IO.puts "#{value} is an integer" end end
By using custom guard functions or regular conditional expressions, you can achieve the same result as overriding built-in guards in Elixir.
How to use operators in Elixir guards?
In Elixir, guards are used in function clauses to add conditions that must be met in order for the function to be evaluated. Operators can be used in guards to compare values and specify conditions.
Here is an example of how to use operators in Elixir guards:
defmodule Math do def is_positive(num) when num > 0 do IO.puts("#{num} is positive") end
def is_negative(num) when num < 0 do IO.puts("#{num} is negative") end
def is_zero(num) when num == 0 do IO.puts("#{num} is zero") end end
Math.is_positive(5) # Output: 5 is positive Math.is_negative(-2) # Output: -2 is negative Math.is_zero(0) # Output: 0 is zero
In this example, we define a module Math with three functions that use operators in guards to check the sign of a number. The > and < operators are used to check if a number is positive or negative, while the == operator is used to check if a number is zero.
By using operators in guards, we can create more specific and flexible function clauses that only get evaluated when certain conditions are met.
What is the error message for failing guards in Elixir?
The error message for failing guards in Elixir is "GuardClauseError".