Exit in Elixir

Here’s an idiomatic Elixir example that demonstrates the concept of exiting a program:

defmodule ExitExample do
  def run do
    # This will not be executed due to the early exit
    Process.flag(:trap_exit, true)

    # Exit with status 3
    System.halt(3)

    # This line will never be reached
    IO.puts("This will not be printed")
  end
end

ExitExample.run()

This Elixir code demonstrates how to exit a program immediately with a specific status code. Let’s break it down:

1. We define a module called ExitExample with a run function.

2. Inside run, we set up a trap for exit signals using Process.flag(:trap_exit, true). This is analogous to the defer statement in the Go example, but it won’t prevent the program from exiting.

3. We use System.halt(3) to immediately exit the program with status code 3. This is equivalent to os.Exit(3) in Go.

4. The IO.puts statement after System.halt(3) will never be executed, similar to the deferred print statement in the Go example.

To run this Elixir script:

1. Save the code in a file named exit_example.exs.
2. Open a terminal and navigate to the directory containing the file.
3. Run the script using the elixir command:

$ elixir exit_example.exs

You won’t see any output because the program exits immediately. To check the exit status:

$ echo $?
3

This will print 3, confirming that the program exited with status code 3.

In Elixir, unlike languages like C or Go, the return value of the main function doesn’t determine the exit status. Instead, you use System.halt/1 to exit with a specific status code.

It’s worth noting that in Elixir, it’s generally preferred to let processes crash and be supervised rather than explicitly exiting the entire application. However, System.halt/1 is available when you need to forcibly terminate the entire Erlang VM with a specific exit code.

This example demonstrates how Elixir handles program termination, which is conceptually similar to the Go example but uses Elixir-specific constructs and best practices.