[erlang-questions] Wanted additions to the maps module?

[Robert Virding]

I missed this thread, but Björn-Egil you know what I want. :-)

maps:first(Map) -> {Key,Value} | error.
maps:next(Key, Map) -> {Key,Value} | error.

Robert


On 13 April 2016 at 15:40, Björn-Egil Dahlberg XB <
bjorn-egil.xb.dahlberg@REDACTED> wrote:

> There is currently no (good) way to get out of C-context to execute some
> erlang snippet and then get back into c-context. Traps does this but only
> in a controlled manner. I think it is doable though.
>
> Your proposal of maps_apply/3 is the maps equivalent of dict:update/3 and
> sadly that name is already occupied in maps (it's the equivalent of
> gb_trees).
>
> I think we should add it to the API without thinking about the performance
> too much. Performance can always be improved later on.
>
> Is maps:apply/3 the best name we can think of? I don't really trust you
> and naming things. =) update/3,4 would probably have been best but c'est la
> vie.
>
> // Björn-Egil
>
>
> On 2016-04-13 13:09, Jesper Louis Andersen wrote:
>
>
> On Fri, Apr 8, 2016 at 8:31 PM, Björn-Egil Dahlberg <
> <wallentin.dahlberg@REDACTED>wallentin.dahlberg@REDACTED> wrote:
>
>> Have you repeated some code or built your own private lib to handle
>> certain maps specific tasks and thought "why isn't this in the maps module?"
>
>
> One function I like to have is "apply update via function", and I
> implement it somewhat often:
>
> maps_apply(F, K, Map) ->
>     V = maps:get(K, Map),
>     maps:put(K, F(V), Map).
>
> But it can be made much faster in a direct implementation since I don't
> have to first pick up the value: I can apply F when I sit with the value at
> hand and thus avoid the "put" lookup path. It might, however, be nasty to
> implement because F is in Erlang-context, whereas the maps operations are
> in BIF-context.
>
>
> --
> J.
>
>
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