Enhancements to dbg in Elixir 1.18
- Daniel Kukula
- Development , Tutorial
- December 22, 2024
Table of Contents
Elixir 1.18 added some interesting features, but one that went under the radar was extended support for dbg. In 1.17 when you had this code:
a = 1
b = 2
if a + b == 3 do
:equal
else
:non_equal
end
|> dbg
It evaluated to:
if a + b == 3 do
:equal
else
:non_equal
end #=> :equal
In 1.18 this was aligned with what case and cond does:
Case argument:
1 + 2 #=> 3
Case expression (clause #1 matched):
case 1 + 2 do
3 -> :equal
_ -> :non_equal
end #=> :equal
if result in 1.18:
If condition:
a + b == 3 #=> true
If expression:
if a + b == 3 do
:equal
else
:non_equal
end #=> :equal
If this is not enough you can wrap your code in brackets and pass it to dbg:
(
input = %{a: 1, b: 2}
c = Map.get(input, :c, 20)
if input[:a] + c == 3 do
:equal
else
:non_equal
end
)
|> dbg
Results in displaying results for every expression:
Code block:
(
input = %{a: 1, b: 2} #=> %{a: 1, b: 2}
c = Map.get(input, :c, 20) #=> 20
if input[:a] + c == 3 do
:equal
else
:non_equal
end #=> :non_equal
)
Last missing piece is the with macro which is sometimes a nightmare to debug, in Elixir 1.18 we have support for that:
with input = %{a: 1, b: 2},
{:ok, c} <- Map.fetch(input, :c),
3 <- input[:a] + c do
:equal
else
_ -> :non_equal
end
|> dbg
The result here is:
With clauses:
%{a: 1, b: 2} #=> %{a: 1, b: 2}
Map.fetch(input, :c) #=> :error
With expression:
with input = %{a: 1, b: 2},
{:ok, c} <- Map.fetch(input, :c),
3 <- input[:a] + c do
:equal
else
_ -> :non_equal
end #=> :non_equal
This should make your debugging journey easier. If you are stuck in older Elixir versions you can install a package that backports this functionality dbg_mate. Thanks for your attention.
