Why is x = x +1 valid in Elixir?

Question

Everything I\'ve read about Elixir says that assignment should be thought of as pattern matching. If so then why does x = x + 1 work in Elixir? There is no value of x for wh

Answer 1

During the pattern matching, the values on the right of the match are assigned to their matched variables on the left:

iex(1)> {x, y} = {1, 2}
{1, 2}
iex(2)> x
1
iex(3)> y
2

On the right hand side, the values of the variables prior to the match are used. On the left, the variables are set.

You can force the left side to use a variable's value too, with the ^ pin operator:

iex(4)> x = 1
1
iex(5)> ^x = x + 1
** (MatchError) no match of right hand side value: 2

This fails because it's equivalent to 1 = 1 + 1, which is the failure condition you were expecting.