Why I get bad argument in arithmetic expression?

Questions / Help
1

I try to delete the last element from a list within a defp in phoenix channel:

passed_params value is ["-0.75", "0.75", "0m", "16.67m", "0m", "0", "16.67m", "0"]

, I tried:

passed_params = List.delete_at(passed_params, length(passed_params)-1)

I get error at that line:

[error] GenServer #PID<0.495.0> terminating
** (ArithmeticError) bad argument in arithmetic expression```

However, if I try the same code in `iex` it works and remove the last element without error
Any idea?
2

You can just do: List.delete_at(passed_params, -1)

3

LostKobrakai already told you how to achieve your goal.

As to why you’re getting the error, it’s likely due to a parsing issue (can’t confirm at the moment): -1 is just a number (negative one). So this would probably work with your original code: List.delete_at(passed_params, length(passed_params) - 1) (note the spaces around the - operator).

4

That’s strange, I tried different ways, including List.delete_at(passed_params, -1) they all work without error in the iex but not in phoenix channel…

5

I’ve doubled checked it, no space…
Why would it fail inside channel?!

6

Does your test for that channel pass? Have you setup socket channel tests?

7

Can you please share full code?

Perhaps the problem is somewhere else?

8

I did not setup socket channel tests, I will try to assemble minimum code that reproduce the issue, thanks