sihui_io
(["a", "b"] -- ["a"]) ++ ["a"] vs ["a", "b"] -- ["a"] ++ ["a"]
iex(71)> (["a", "b"] -- ["a"]) ++ ["a"]
["b", "a"]
iex(72)> ["a", "b"] -- ["a"] ++ ["a"]
["b"]
Hi team,
Why having the () makes the difference?
Is there a term for this behavior?
Thanks!
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First 6 of 6 Posts!
NobbZ
This is called operator precedence and associativity. You can take a look at the precedence table in the documentation.
The precedence of both operators (
--and++) is the same, so they wil be applied in order of their associativity which is “right to left”.So
a -- b ++ cis equivalent toa -- (b ++ c).sihui_io
Thanks! That makes sense now! Do you know why – and ++ are being applied from right to left instead of left to right?
fmcgeough
Operator precedence is defined at: https://hexdocs.pm/elixir/master/operators.html
sihui_io
Thanks fmcgeough. I do see the table. I guess my question is what’s the reason behind having the associativity for ++ and – to be right to left instead of left to right.
fmcgeough
ah. gotcha. Its a good question. I know the Erlang precedence is the same. But as for why.. sorry. I’m not sure why that choice was made.
sihui_io
I see. It makes sense that elixir gets it from Erlang. Thanks!