crisefd
With statement with arrow or match operator. Wha'ts the difference?
I’ve been working wit Elixir for a few weeks. Quick question:
In the next code, What’s the difference between the first two
left = right
and the last
left <- right
I only’ve used with with the <- before.
with {:ok, item} = Item.createl(%{ name: "Sample Item", item_id: id }),
{:ok, option} = Option.create_option(%{ title: "Sample Choice", item_id: item.id }),
option <- Repo.preload(option, :item)
do
...
end
Marked As Solved
NobbZ
From the documentation:
The behaviour of any expression in a clause is the same as outside. For example,
=will raise aMatchErrorinstead of returning the non-matched value:with :foo = :bar, do: :ok #=> ** (MatchError) no match of right hand side value: :bar
An example that is a bit more obvious:
iex(1)> with :a = :b do :ok else _ -> :error end
warning: "else" clauses will never match because all patterns in "with" will always match
iex:1
** (MatchError) no match of right hand side value: :b
(stdlib) erl_eval.erl:453: :erl_eval.expr/5
(stdlib) erl_eval.erl:126: :erl_eval.exprs/5
(iex) lib/iex/evaluator.ex:257: IEx.Evaluator.handle_eval/5
(iex) lib/iex/evaluator.ex:237: IEx.Evaluator.do_eval/3
(iex) lib/iex/evaluator.ex:215: IEx.Evaluator.eval/3
(iex) lib/iex/evaluator.ex:103: IEx.Evaluator.loop/1
iex(1)> with :a <- :b do :ok else _ -> :error end
:error
4
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