Epxir - Typespecs

Epxir is a dynamically typed language, so all types in Epxir are inferred by the runtime. Nonetheless, Epxir comes with typespecs, which are a notation used for declaring custom data types and declaring typed function signatures (specifications).

Function Specifications(specs)

By default, Epxir provides some basic types, such as integer or pid, and also complex types: for example, the round function, which rounds a float to its nearest integer, takes a number as an argument (an integer or a float) and returns an integer. In the related documentation, the round typed signature is written as −

round(number) :: integer

The above description imppes that the function on the left takes as argument what is specified in parenthesis and returns what is on the right of ::, i.e., Integer. Function specs are written with the @spec directive, placed right before the function definition. The round function can be written as −

@spec round(number) :: integer
def round(number), do: # Function implementation
...

Typespecs support complex types as well, for example, if you want to return a pst of integers, then you can use [Integer]

Custom Types

While Epxir provides a lot of useful inbuilt types, it is convenient to define custom types when appropriate. This can be done when defining modules through the @type directive. Let us consider an example to understand the same −

defmodule FunnyCalculator do
   @type number_with_joke :: {number, String.t}

   @spec add(number, number) :: number_with_joke
   def add(x, y), do: {x + y, "You need a calculator to do that?"}

   @spec multiply(number, number) :: number_with_joke
   def multiply(x, y), do: {x * y, "It is pke addition on steroids."}
end

{result, comment} = FunnyCalculator.add(10, 20)
IO.puts(result)
IO.puts(comment)

30
You need a calculator to do that?