Proposal to expand Enum.split_with/2 with post-process function option
similar to how it implemented in Enum.group_by/3 with third argument.
In my experience it is an often case when you need to split a enum through
a function with a spec like:
@spec foo(term) :: {:ok, result_t} | {:error, error_t}
and receive two enums, where one contains successful results and another
contains errors like: {list(result_t), list(error_t)}.
Enum.map/2 + Enum.split_by/2 seems to be a good choice for this work but
unfortunately split_by it doesn't support post-process function (like third
argument of Enum.group_by/3 does) so result of applying Enum.split_with/2
will be: {list({:ok, result_t}, list({:error, error_t})} instead.
I propose to expand Enum.split_with to this signature:
@spec split_with(t <https://hexdocs.pm/elixir/Enum.html#t:t/0>(), (element
<https://hexdocs.pm/elixir/Enum.html#t:element/0>() -> as_boolean
<https://hexdocs.pm/elixir/typespecs.html#built-in-types>(term
<https://hexdocs.pm/elixir/typespecs.html#built-in-types>())), (element
<https://hexdocs.pm/elixir/Enum.html#t:element/0>() -> any
<https://hexdocs.pm/elixir/typespecs.html#basic-types>())) :: {list
<https://hexdocs.pm/elixir/typespecs.html#built-in-types>(), list
<https://hexdocs.pm/elixir/typespecs.html#built-in-types>()}
split_with(enumerable, split_fun, transform_fun \\ fn x -> x end)
so it can be used like this:
{successful_results, errors} =
mu_enum
|> Enum.map(&foo/1)
|> Enum.split_by(& match?({:ok, _}, &1), fn {_, res} -> res end)
Because of lack of transform_fun in current implementation an additional
step needed:
{Enum.map(successful_results, fn {_, res} -> res end), Enum.map(errors, fn
{_, res} -> res end)}.
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