proposal: Map.replace/3

[Kensei N]

Hi !

I propose Map.replace/3.

Map.replace!/3 already exists.

However, it is difficult to use pattern match with Map.replace!/3  because it raise error when key is not present in map.

So, I think it is a good idea make Map.replace/3  and it return

:error

when key is not present in map, and it return

{:ok, %{hoge: "hoge"}}

when key is present and work correctly.

Example:

 iex> ex_map = %{a: 1, b: 2}
%{a: 1, b: 2}

 iex>Map.replace(ex_map, :a, 3)
{:ok, %{a: 3, b: 2}}

 iex>Map.replace(ex_map, :hoge, 3)
:error

[Fernando Tapia Rico]

Hi Kensei,

Here is a bit of context :)

There was a Map.replace/3 (with a different behavior) that was deprecated in favor of Map.fetch/2 + Map.put/3. Here is a link to the code: 

https://github.com/elixir-lang/elixir/blob/master/lib/elixir/lib/map.ex#L304

Here is the rationale behind the deprecation: 

https://github.com/elixir-lang/elixir/commit/a81a17b3b09b267883383bdb8a00fe00ab2724a8

Hope this helps :)

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