Re: [elixir-talk:13544] Re: Dealing with complicated nesting in API JSON requests in a functional way

[Peter Hamilton]

This is a fairly straightforward (though a bit long) for comprehension:

for {room_id, room} <- data,
      {date, obj} <- room,
      stuff = obj["important_stuff"],
      {child_id, child} <- stuff,
      child_id != "id" do
  %{
      room_id: room_id,
      date: date,
      ...
   }
end

On Tue, Jul 26, 2016, 9:45 PM Sam Hains <sdha...@gmail.com> wrote:

That should read:  triple nested Enum.each ****

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[Pierre de Lacroix]

In a comprehension like this, what's the difference between pattern
matching with "<-" and "=" ?

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[José Valim]

<- will traverse the collection on the right side matching each element with the pattern on the left side. = is the = we all know and love.

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José Valim

www.plataformatec.com.br

Skype: jv.ptec

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[Pierre de Lacroix]

OK, because it's in a for. I've seen that both could be used in a with construct too, do they have the same meaning in this case ?

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[José Valim]

In with <- matches the value on the right to the pattern on the left, only continuing if they match. The difference is that "for" traverses the collection on the right while "with" takes the value on the right at "face value". = has the same meaning on both expressions which is the same as in any other Elixir code. In other words, <- slightly changes its meaning based on the wrapping construct.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-talk/151BBF7E-59C6-45F4-9DA3-5D7C214FCD80%40gmx.com.