Parsing JSON arrays of integers in Elixir

Question

If I have a JSON object where the value of a key is an array of integers, and each integer of the array just happens to correspond with the code point of a printable ASCII character, is there any way that I can have Elixir interpret the array as just a plain list of integers and not as a char list?

I've used three different Elixir JSON parsers in an attempt to get a list of integers returned, but they all return the char representation of the list:

elixir-json:

iex> JSON.decode!(~s({ "foo": [35, 35] }))
%{"foo" => '##'}

exjsx:

iex> JSX.decode!(~s({ "foo": [35, 35] }))
%{"foo" => '##'}

poison:

iex> Poison.decode!(~s({ "foo": [35, 35] }))
%{"foo" => '##'}

What I would like is just %{"foo" => [35, 35]}. Is this possible, or am I missing something? If it's not possible, how should I be decoding this value from JSON into Elixir, and then how would I encode it back into a JSON array should I need to send the JSON on to some other external system?

Edit

Thanks to michalmuskala's answer, I think something clicked, and then with some further investigation, I realised there was really nothing to worry about when it comes to the parsing JSON integer arrays in and out of Elixir:

iex> json = Poison.decode!(~s({ "foo": [35, 35] }))
%{"foo" => '##'}
iex> Poison.encode!(json)
"{\"foo\":[35,35]}"

michalmuskala · Accepted Answer · 2015-11-29 00:45:28Z

2

The returned result is perfectly fine and correct. '##' and [35, 35] is exactly the same thing in Elixir. It's just a different way to represent the same value.

iex> [35, 35] == '##'
true
iex> inspect [35, 35]
"'##'"
iex> inspect [35, 35], char_lists: :as_lists
"[35, 35]"

This is confusing at first, but there is a strong reason behind it. Majority of Erlang libraries use lists of chars (or charlists) as strings and not binaries as Elixir. For the ease of interoperability, if a list contains only printable characters it will be, by default, printed as a single quoted string. But this does not change what data is behind it - it's only a different representation of the same value.

answered Nov 29, 2015 at 0:45

michalmuskala

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1 Comment

Paul Fioravanti Over a year ago

I think the final sentence of your answer got something to finally click in my head, so thanks very much for that!

Zepplock · Accepted Answer · 2015-11-29 00:53:49Z

0

It's a list:

iex(16)> '##' |> is_list
true

And you can do regular List operations on it:

iex(15)> '##' |> List.first
35

answered Nov 29, 2015 at 0:53

Zepplock

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