You can have the value of a variable depending on some condition.

In other languages you see code like the following which would not work in Elixir due to elixirs scoping rules:

a = 2
if condition then:
    a = 1

if suppose you want to change any variable value inside if block in Elixir. You need to get back and re-assign the value to the same variable.

This is the code you will expect to work. But it won’t.

iex(7)> a = 5
5
iex(8)> is_odd = nil
nil
iex(9)> if rem(a, 2) == 0 do
...(9)>   is_odd = false
...(9)> else 
...(9)>   is_odd = true
...(9)> end
warning: variable "is_odd" is unused (if the variable is not meant to be used, prefix it with an underscore)
  iex:12

warning: variable "is_odd" is unused (if the variable is not meant to be used, prefix it with an underscore)
  iex:10

true
iex(10)> is_odd
nil

So you need to re-assign it back like below:

iex(13)> a = 5
5
iex(14)> 
nil
iex(15)> is_odd = if rem(a, 2) == 0 do
...(15)>   false
...(15)> else 
...(15)>   true
...(15)> end
true
iex(16)> is_odd
true
iex(17)> 

There was a warning about the “imperative assignment” from 1.2 or 1.3 on, and it actually worked until 1.8 or 1.9…