[erlang-questions] No JSON/MAPS interoperability in 17.0?

Thomas Lindgren <>
Fri Mar 14 18:04:43 CET 2014



Hey OTPeople,

Since this comes up every now and then, does Ericsson have any plan to introduce atom garbage collection or suchlike in Erlang/OTP? Some official info would be great.

Best,
Thomas




On Friday, March 14, 2014 4:20 PM, Fred Hebert <> wrote:
 
Hi Joe,
>
>I think the library you have described (does 99% of the work) is the
>equivalent of bait-and-switch at the language/library level:
>
>1) it's not just a question of do floating point numbers survive the
>   roadtrip, but also integers.
>2) json tags are more or less strings and expect utf-8. Currently, we
>   'support' utf8 atoms but we don't. See
>   http://www.erlang.org/erldoc?q=list_to_atom.
>   This doesn't mention what you do in case of trying to encode a map
>   which currently uses keys such as '1.0', 1.0, <<"1.0">>, and "1.0" at
>   the same time. We currently have 4 data types that will possibly need
>   an identical representation while being converted.
>
>   Woops, that doesn't work super well and may in fact cover far less
>   than 99% of the cases. We have to consider all the other cases such
>   as just 1, 1.0, "1.00", "1.000", ..., and so on.
>
>
>3) That can be made to work
>4) No opinion on this one
>5) This can also be read as "best effort not corrupting values read"
>   which scares me a lot if the end result is not "raise an error when you can't
>   figure it out reliably"
>6) Amen to that.
>
>This doesn't even take into account the issue that by using atoms by
>default, you're actively using a source of memory leaks into the
>library. This guarantees that every tutorial out there will recommend
>not using the standard library for your tasks.
>
>What I'm getting at here is that while your scheme might work for 99% of
>possible JSON -> Erlang decodings, it will do so in a risky way that
>cannot be advocated.
>
>If you consider all the possible Erlang -> JSON mappings (and this is
>where the biggest problem always is), then it covers far, far less than
>99% of the cases, because there is not one good way to do it (how do you
>even represent binaries that are not UTF-8 and distinguish them from
>actual strings? You validate the entire thing unless you want to create
>unparseable JSON).
>
>I used the words bait-and-switch and I mean it there. This is one of the
>points where Jose Valim and I disagree the most.
>
>I hate, absolutely hate solutions that bring you 70% of the way (to use
>a number we discussed between ourselves). Why? Because you start by
>learning the 70% solution and then it doesn't work. Suddenly you have to
>go out and look for the 99% and the 100% solutions out there.
>
>Except you now have a crusty code base full of legacy, and you start
>supporting, one, two libraries, which you never envisioned. And you find
>out you're married to encoders and decoders that decided to do things
>differently, but you just don't have the time to fix everything right
>now.
>
>You start seeing node crashes because someone decided atoms is a good
>way to receive unvalidated data without first having implemented a
>scheme to GC them (say EEP-20:
>http://www.erlang.org/eeps/eep-0020.html).
>
>You start being pretty angry that a language so focused on getting
>productions systems live has a standard library that lets you hang dry.
>
>Then you get even angrier when you figure out a crapload of frameworks
>in the wild all use that faulty function because it was in the standard
>library.
>
>Then you get certainly extremely angry and leave for Go or some other
>language when you figure out the community already had solutions to
>these problems in the year 2014 (and before!) but they were just
>overlooked because we wanted an easy JSON implementation in the stdlib.
>
>I can't for the life of me see the benefit of canonizing a bad library
>when tradeoffs are already known and worked around in the wild.
>
>What we should focus on is explaining these tradeoffs and making it easy
>to show the different options. Currently, picking a JSON lib is hard
>because there is such a very poor match between what you can possibly
>encode in Erlang and how you can translate this back and forth with
>JSON. Not just because it's not in the standard library.
>
>Not speaking about the problem doesn't make it go away, it makes it more
>surprising, which is not a desirable property.
>
>Regards,
>Fred.
>
>On 03/14, Joe Armstrong wrote:
>
>> This is what most libraries do - they work 99% of the time.
>> 
>> (( the 99% is horrible - just when I think a library is great I find - *but
>> I can't do X* then
>>     I'm in trouble - but I guess this is in the nature of the beast - only
>> pure mathematical
>>     functions have the kind of "platonic interfaces" that will never change
>> - real
>>     world problems with time and space involved are just plain messy ))
>> 
>> If we freeze the JSON design and say:
>> 
>>     1) floating point number will not survive a round-trip
>>     2) JSON tags will be erlang atoms
>>     3) Terms are not-infinite and rather small (few MB at max)
>>     4) we want a parse tree
>>     5) best effort at sorting out character set encodings
>>     6) Pure erlang
>> 
>> Then the problem becomes "easy" and can be knocked out in a few lies of code
>> using maps:from_list and maps:to_list.
>> 
>> And *because* it's easy nobody writes a library to do this.
>> 
>> The trouble is a beginner probably does not find this easy and would
>> appreciate
>> a library that worked 99% of the time on simple problems.
>> 
>> /Joe
>> 
>
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