It's functionality that is very specific to a particular use case to be
added to a standard library module. Plus, it either needs to create new
atoms (which standard library will never do) or fail for some inputs (which
is again not generally useful):
iex(1)> m = %{key_1: :val_1, key_2: :val_2}
iex(4)> m |> Map.take([:key_1, :key_2]) |> Map.new(fn {key, val} ->
{String.to_existing_atom("prefix_#{key}"), val} end)
** (ArgumentError) argument error
:erlang.binary_to_existing_atom("prefix_key_1", :utf8)
(stdlib) erl_eval.erl:680: :erl_eval.do_apply/6
(stdlib) erl_eval.erl:888: :erl_eval.expr_list/6
(stdlib) erl_eval.erl:240: :erl_eval.expr/5
(elixir) lib/map.ex:216: Map.new_transform/3
iex(4)> :prefix_key_1
:prefix_key_1
iex(5)> :prefix_key_2
:prefix_key_2
iex(6)> m |> Map.take([:key_1, :key_2]) |> Map.new(fn {key, val} ->
{String.to_existing_atom("prefix_#{key}"), val} end)
%{prefix_key_1: :val_1, prefix_key_2: :val_2}
On Fri, Sep 20, 2019 at 4:07 PM Tiago Botelho <tiagonbote...@gmail.com>
wrote:
> A common pattern that I've found myself using is having to prefix a few
> keys (namely `ids`) which I do with following approach:
>
> ```
> %{}
> |> Map.put(:prefix_key_1, map.key_1)
> |> Map.put(:prefix_key_2, map.key_2)
>
> => %{prefix_key_1: :val_1, prefix_key_2: :val_2}
> ```
>
> or
>
> ```
> %{prefix_key_1: map.key_1, prefix_key_2: map.key_2}
>
> => %{prefix_key_1: :val_1, prefix_key_2: :val_2}
> ```
>
> It seems to me that we already have good functionality for taking specific
> keys out of a map by using Map.take/2
> (which is effectively the same thing we are doing in the examples above)
> but no good way of bulk updating specific key names.
>
> My proposal would be to be able to pass a `prefix` as an option to
> `Map.take` which would look roughly like the following:
>
> ```
> Map.take(map, [:key_1, :key_2, :key_3], prefix: :prefix)
>
> => %{prefix_key_1: :val_1, prefix_key_2: :val_2, prefix_key_3: :val_3}
> ```
>
> Pros:
>
> * A simpler interface to take keys from a map and "rename" them according
> to the context they will be used for
>
> Cons:
>
> * Using the `prefix` option would mean that all the keys would get
> prefixed, a mixed approach would still require the examples showed above.
> * Might make Map.take do too much at once
>
> Since the Cons might be might seem to discourage this approach, another
> proposal would be to introduce Map.prefix/2 and Map.suffix/2 which would
> only
> update the chosen keys in a map like so:
>
>
> ```
> map
> |> Map.take([:key_1, :key_2, :key_3, :key_4])
> |> Map.prefix([:key_3, :key_4], :prefix)
>
> => %{key_1: :val_1, key_2: val_2, prefix_key_3: :val_3, prefix_key_4:
> :val_4}
> ```
>
> Interested in hearing your thoughts 😊
>
> Thank you,
> Tiago
>
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