I have wrote a version for this in our project. It behaves exactly like
Map.merge/2 but concating lists and merging inner maps:
```
# @spec merge_cat(map, map) :: map
def merge_cat(e, acc), do: Map.merge(acc, e, &combiner/3)
defp combiner(_, l1, l2) when is_list(l1) and is_list(l2), do: l1 ++ l2
defp combiner(_, m1, m2) when is_map(m1) and is_map(m2), do:
merge_cat(m1, m2)
defp combiner(_, _, v2), do: v2
```
On Wed, Sep 7, 2016 at 6:02 AM, Brian Cardarella <br...@dockyard.com> wrote:
> This is assuming that all nested values are maps all the way down. What
> happens in the event of a Keyword list for example? Or a tuple? If the
> use-case is limiting itself to just maps of maps this works. But if the
> wider use-case should be supported it may make sense to consider a
> Kernel.deep_merge that has indifferent access support for the values to be
> merged.
>
>
> On Tuesday, September 6, 2016 at 2:41:22 PM UTC-4, OvermindDL1 wrote:
>>
>> I had made my own a few times, though rare, it could be useful. Unsure
>> about it in core but in a library definitely.
>>
>> On Tuesday, September 6, 2016 at 9:20:23 AM UTC-6, Tobias Pfeiffer wrote:
>>>
>>> Hi everyone,
>>>
>>> in Elixir we work a lot with maps (or at least I do :D). And we know and
>>> love Map.merge. However given a map like %{a: %{b: 1}} and we want to
>>> merge it with a map like %{a: %{c: 2}} then the :a key will be totally
>>> overridden with whatever is supplied in the other map.
>>>
>>> However, for instance for configuration, what we might want is the
>>> result to be %{a: %{b: 1, c: 2}} - e.g. if the value is a map on both
>>> sides recursively merge that as well.
>>>
>>> It is rather simple to implement in elixir with Map.merge/3 [1] but I
>>> think it'd still be helpful to have it in elixir core (otherwise I'll
>>> make a mini hex package :D). E.g. it is useful and it'll keep people
>>> from wondering about it or writing their own a little flawed
>>> implementations.
>>>
>>> So, what do you think - Map.deep_merge in elixir-core - yay/nay? I'm
>>> happy to draft a PR if it gets the sign of approval.
>>>
>>> Tobi
>>>
>>>
>>> [1] http://stackoverflow.com/a/38865647/1810896
>>> --
>>> http://www.pragtob.info/
>>>
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