One composes; one doesn't.
On Mon, Oct 12, 2020 at 7:25 AM José Valim <[email protected]> wrote:
> Hi everyone,
>
> I thought I had commented on this thread but apparently I have not, so
> apologies for the delay.
>
> I am not convinced about this functionality because I honestly do not find
> this:
>
> new_map =
> post
> |> Map.rename_key(:user_id, :author_id)
> |> Map.rename_key(:body, :content)
>
> clearer than this:
>
> new_map = %{
> user_id: post.author_id,
> content: post.body,
> ...
> }
>
> Maybe if you want to keep the other keys as is, then "rename_key" can be
> handy, but even then, what happens if you add a new key to post? Does it
> automatically appear in the new_map? Or should it not?
>
> Even if we say that "clearer" is personal, there are practical reasons for
> preferring the latter, such as the runtime can optimize it better (as all
> keys are literals and the map is not built dynamically), and it is easier
> to typecheck maps with known keys.
>
> So my $.02 here is that this is not something I would necessarily endorse
> and, if you really want to rename only certain keys inside a map, you can
> do it with a helper function or by using put+drop on the desired keys.
>
> Thanks!
>
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