Elixir 1.14’s dbg/2 function

Elixir 1.14 introduced the dbg/2 function, which inspects and prints a passed value. It also adds the curent location to the log output, which is useful for finding the debug statement later.

dbg(~N[2000-01-01 23:00:07.123])

[lib/phoenix_example_web/controllers/page_controller.ex:10: PhoenixExampleWeb.PageController.home/2]
~N[2000-01-01 23:00:07.123] #=> ~N[2000-01-01 23:00:07.123]

The dbg/2 function prints the code passed to it, which is especially useful when adding it to a pipeline, where it will show the return values of each item:

~N[2000-01-01 23:00:07.123]
|> NaiveDateTime.truncate(:second)
|> NaiveDateTime.to_iso8601()
|> dbg()

[lib/phoenix_example_web/controllers/page_controller.ex:10: PhoenixExampleWeb.PageController.home/2]
~N[2000-01-01 23:00:07.123] #=> ~N[2000-01-01 23:00:07.123]
|> NaiveDateTime.truncate(:second) #=> ~N[2000-01-01 23:00:07]
|> NaiveDateTime.to_iso8601() #=> "2000-01-01T23:00:07"

Printing the location already makes it a good replacement for IO.inspect/2, but the dbg/2 function also starts the debugger when in an IEx shell:¹

Request to pry #PID<0.625.0> at PhoenixExampleWeb.PageController.home/2 (lib/phoenix_example_web/controllers/page_controller.ex:7)

    4:   def home(conn, _params) do
    5: 
    6: 
    7:     ~N[2000-01-01 23:00:07.123]
    8:     |> NaiveDateTime.truncate(:second)
    9:     |> NaiveDateTime.to_iso8601()
   10:     |> dbg()

Allow? [Yn]

1. This works with Phoenix applications as well, if they’re started with an attached IEx shell:

   iex -S mix phx.server
   

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