scala/scala

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Rob Norris

@tpolecat

Yeah it's IEEE 754 floating point so you get 52 bits of mantissa and 12 bits of exponent. At least in Javascript. I don't know if JSON itself specifies it.

Martijn Hoekstra

@martijnhoekstra

Json specifies arbitrary precision

Rob Norris

@tpolecat

Ok.

nafg

@nafg

@Daenyth parsing it with what?

Gavin Bisesi

@Daenyth

JSON.parse

Martijn Hoekstra

@martijnhoekstra

But stresses that if you want to be interoperable, you probably need to do IEEE or you'll probably have a bad time

Gavin Bisesi

@Daenyth

@tpolecat json doesn't "specify" much

nafg

@nafg

@Daenyth in Javascript? Javascript doesn't have Double or Long

Gavin Bisesi

@Daenyth

the json "spec" is that all json numbers are infinite-length perfect precision

@nafg yes, that's why I said number

The context is that I have a jvm backend that has Long values as ids for certain things, and javascript is awful

Martijn Hoekstra

@martijnhoekstra

With an "but if you do that, you're sort of asking for it" disclaimer

Gavin Bisesi

@Daenyth

I wish there was some consensus on a "reasonable json" spec

nafg

@nafg

@Daenyth JSON.parse is in javascript, not on the JVM

Gavin Bisesi

@Daenyth

Yes.

I'm aware of that

nafg

@nafg

I'm sure you are but there's still a lot that I'm missing

Gavin Bisesi

@Daenyth

JVM backend, js (ts) frontend. JSON between.
An api didn't work right because the frontend was rounding certain identifier values, which were Long on the jvm and serialized as json numbers

that's all there is to it

nafg

@nafg

Ah yes, I had that recently

Mainly in a property test using Nyaya

Now I have

  val genJsSafeLong = Gen.chooseLong(-9007199254740991L, 9007199254740991L)

Rob Norris

@tpolecat

We ran into it with timestamps.

GraphQL has real numeric types, which is nice.

nafg

@nafg

I mean in my case it's only an issue because Circe for scala.js relies on JSON.parse

IIRC upickle doesn't have that issue

i.e. there's nothing stopping you from parsing JSON in a scala-friendly way in scala.js. It will probably be slower, of course

Oh right -- upickle avoids it by representing Longs as a string

it doesn't use json number for longs

You can customize circe to do that also

Rob Norris

@tpolecat

:musical_note: string, string, string, string, everybody loves string

nafg

@nafg

It's better than bytes...

sometimes, anyway

Rob Norris

@tpolecat

could be worse

nafg

@nafg

I mean JSON is a string representation

Li Haoyi

@lihaoyi

you can actually tell uPickle to use numbers to represent longs, nowadays we have our own JSON parser written in scala.js that is competitive with JSON.parse

not necessarily a good idea though; who knows what other non-uPickle JSON libraries you may be interacting with that will truncate your longs to 64bit doubles

M Karthick

@mkartic

I've recently run into a file at work which was just a C struct instance dumped into a file. How would I go about parsing this in scala?

Something like, struct {char a; char b[5];} will have 'ABB$$$' (where $ denotes NUL).

I can probably read the file into a byte array, and convert it by hand. Is there a better way?

nafg

@nafg

Better by what metric?

How much of this do you need to do?

M Karthick

@mkartic

@nafg Better as in, whatever I've come up with sounds like the most naive approach possible. Wondering if there might be a more elegant way to do this.

Fairly often, as we have to parse this byte file on a regular basis.

nafg

@nafg

Right but is it just this one file and this one struct format? And how complex is it?

M Karthick

@mkartic

Its just this one struct format. But there are about 10 fields of varying lengths.

All the fields are primitives. Either strings or ints.

nafg

@nafg

The simplest thing that comes to mind that might make it a bit higher-level is DataInputStream but I'm not sure if it will necessarily do the right thing.

The full-on high level solution would probably be scodec

I'm just not sure if bringing it in would be overkill for your scenario

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