Testing for Decimal Data Type in Elixir?

Question

Is there an equivalent of is_string, is_number, is_integer, is_binary for the Elixir Decimal package?

If not, what are some of the ways to pattern match for a Decimal?

Answer 1

Decimal is an Elixir struct. So, you can match on it with %Decimal{}. This can be added to your function clause or in case statements. Here are couple examples:

def add(%Decimal{} = x, %Decimal{} = y), do: Decimal.add(x, y)

case num do
  %Decimal{} = x -> # ...
  num when is_integer(num) -> # ...
  _ -> # default case
end

The same approach applies for matching any Elixir struct. The matching rules are similar to maps. However, a struct contains only the fields they are defined with and all those fields are present in the struct.

This means that you cannot matching on presence of a file must be done on the default value. For example:

# to match a struct that contains the `:mode` key you can do this:

def my_fun(%{mode: _}), do: # matches if the :mode key is present
def my_fun(%{}), do: # default case when map does not contain the :mode key

# to do the same with a struct

def MyStruct do
  defstruct mode: nil, other: true
end

def my_fun(%MyStruct{mode: mode}) when not is_nil(mode), do: # do something with mode
def my_fun(%MyStruct{}), do: # default case when mode is nil