Late to the discussion, just facing the same issues and wanted to update with the documentation. Maybe things have changed since the posting of this!
https://hexdocs.pm/elixir/1.10.3/patterns-and-guards.html#custom-patterns-and-guards-expressions
Such a guard would look like this:
def my_function(number) when is_integer(number) and rem(number, 2) == 0 do
# do stuff
end
It would be repetitive to write every time we need this check. Instead you can use defguard/1 and defguardp/1 to create guard macros. Here’s an example how:
defmodule MyInteger do
defguard is_even(term) when is_integer(term) and rem(term, 2) == 0
end
and then:
import MyInteger, only: [is_even: 1]
def my_function(number) when is_even(number) do
# do stuff
end
While it’s possible to create custom guards with macros, it’s recommended to define them using defguard/1 and defguardp/1 which perform additional compile-time checks.
