Ever wanted to just build a nice json in kotlin, but found raw string templates hard to keep pretty?...

Big Chungus

10/14/2021, 10:53 AM

Ever wanted to just build a nice json in kotlin, but found raw string templates hard to keep pretty? Well turns out you can make full json DSL with just a few lines of code.

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mind blown 3

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Big Chungus

10/14/2021, 11:00 AM

Serializes to this

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{
  "boolean": true,
  "number": 1,
  "string": "str",
  "null": null,
  "array": [
    1,
    "str",
    null,
    {},
    [
      1,
      "2",
      null,
      3
    ]
  ],
  "object": {
    "boolean": true,
    "number": 1,
    "string": "str",
    "null": null,
    "array": [
      1,
      "str",
      null
    ]
  }
}

Robert Jaros

10/14/2021, 11:05 AM

Serializes with what? kotlinx.serialization?

Big Chungus

10/14/2021, 11:06 AM

With whatever you choose. This just builds a map representation of json.

Big Chungus

10/14/2021, 11:06 AM

i.e. It doesn't depend on any serialization voodoo to work.

Big Chungus

10/14/2021, 11:07 AM

But for transparency, I ran the generated map through Jackson to get that json output.

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arekolek

10/14/2021, 12:17 PM

You can also use the "inject language" feature in the IDE

Screen Recording 2021-10-14 at 14.14.59.mov

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Big Chungus

10/14/2021, 12:26 PM

I'm aware, but I found that hard to maintain in terms of formatting. Plus it adds lots of

that just feels unnatural. I found the DSL much more comfortable to work with as it closer matches json structure and allows direct references to variables (no

required)

Javier

10/14/2021, 2:07 PM

kotlin serialization had something similar to this no? but they changed to

build...

functions

Big Chungus

10/14/2021, 2:09 PM

Did they? I'm not aware of that. Got a link?

Javier

10/14/2021, 2:10 PM

I can't found one, it was removed a lot of months ago

Javier

10/14/2021, 2:13 PM

by

can't be replaced by

operator fun equals

Big Chungus

10/14/2021, 2:20 PM

Hmm, good idea! Or +=

Big Chungus

10/14/2021, 2:20 PM

Not sure which is better

Javier

10/14/2021, 2:35 PM

personally when I create manually a Json I always fail and I use = instead of :

Javier

10/14/2021, 2:36 PM

that is the reason I thought in = hahah

Javier

10/14/2021, 2:37 PM

any way, are you going to publish it as KMP library? not a lot of code, but it can be used in a lot of projects so avoid copypasting can be great

Tobias Berger

10/14/2021, 2:41 PM

something interesting I saw in a DSL for JSON objects once: instead of the

by

infix function, you could implement a

rangeTo

operator function, so

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{
    "number" by 1
}

becomes

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{
    "number"..1
}

which looks a bit like the

just fell over 😄

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Tobias Berger

10/14/2021, 2:45 PM

@Javier

equals

already exists on every type and extension functions can't override member functions. Also, it would result in the usage of

==

, not

and wouldn't work properly with null values (if I remember the behaviour correctly)

jimn

10/14/2021, 3:04 PM

i like operator %, it has two dots also https://gist.github.com/jnorthrup/51f2b23bde522bb03d74aa552c295f6b it feels like there are some wicked delegation opportunities

Javier

10/14/2021, 3:06 PM

ah, not sure if

can be used or only

==

Tobias Berger

10/14/2021, 3:08 PM

assigns a value, the equality check is always

==

Javier

10/14/2021, 3:09 PM

yeah, but there is no another operator for it no?

Javier

10/14/2021, 3:11 PM

maybe

to

to keep consistence with languages features if

cant be used

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jimn

10/14/2021, 3:39 PM

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infix operator fun String.rem(value: Any?) = this `⁚` value //two escaped dots if inlined
    
    @JSSetterDsl
    /**
     * set primitive
     */
    infix fun String.`⁚`(t: Any?) { map[this] = t }  
...
val `{}` by lazy { JSObj().apply(fun JSObj.() = Unit) }

some options. alternatives to backticks would be great in kotlin.

Big Chungus

10/14/2021, 3:53 PM

Backticks are a big nono for mpp projects thanks to js 😀

Javier

10/14/2021, 4:01 PM

and they are hard to write, sadly

Big Chungus

10/14/2021, 5:05 PM

Ok well, I went ahead and published that as an MPP lib 😄 It even builds json strings for you! kon@1.0.0 is out! All proposed setters are supported with the exception of

==

and backticks.

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🆒 1

Javier

10/14/2021, 6:44 PM

Copy code

Modules
kon - wrapper module

Javier

10/14/2021, 6:44 PM

this link is broken

Big Chungus

10/14/2021, 6:45 PM

What do you mean?

Big Chungus

10/14/2021, 8:02 PM

Nvm, figured it out and fixed it

Oliver.O

10/14/2021, 9:01 PM

I like the idea but I'm worried about the operator overkill: Code written by multiple persons can become hard to read if one person would use

by

, the second adds stuff with

, and so on. I'd stick with the usual

to

as this aligns with Kotlin map notation, and avoid synonymous operators.

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Big Chungus

10/14/2021, 10:38 PM

I had same thoughts. I'll use it in my own projects for the next week and will decide on what feels most natural. The rest will be removed. Also I'm a bit iffy about using to as there's an infix function like that in stdlib already used to build pairs. Shadowing might be an issue

Javier

10/14/2021, 10:47 PM

I think

to

is enough and it is used to build maps, I like += too.

Big Chungus

10/14/2021, 11:49 PM

How about just +? It's the same hey on the keyboard

Big Chungus

10/14/2021, 11:49 PM

Although it doesn't convey the intent as well...

Javier

10/15/2021, 2:01 AM

+ for standalone values is fine, but in json there are not standalone values, semantically looks strange

ephemient

10/15/2021, 9:20 AM

did anybody bring up the json builders in kotlinx.serialization? they're a bit more verbose but they do exist (buildJsonObject, buildJsonArray, etc.)

Untitled.kt

Big Chungus

10/15/2021, 9:22 AM

@Javier did but couldn't get a link 😄 Also to get them you have to bring in entire serialization lib (heavy), which might not always be what you want.

Javier

10/15/2021, 9:24 AM

Maybe you can find the commit where they moved to

build...

Javier

10/15/2021, 9:24 AM

Another cool thing you can add to your lib, is compatibility with Kotlin Serialization

Javier

10/15/2021, 9:25 AM

so you generate a

JsonElement

with your syntax

Big Chungus

10/15/2021, 9:25 AM

I'm thinking of adding that as a new module. So ppl could still use it without serialization

ephemient

10/15/2021, 9:27 AM

https://github.com/Kotlin/kotlinx.serialization/pull/881 - before kotlinx.serialization-1.0.0

Oliver.O

10/15/2021, 11:09 AM

@ephemient Thanks for bringing that up. Some thoughts: The

kotlinx.serialization

API seems to ease onboarding (with IDE support, you'd just type

put

and use completion). I am undecided whether its verbosity might increase reading/scanning time when compared to a map-like

to

notation. Probably not much, if at all. In the end, I tend to think it is like using different indentation styles: While I do prefer certain styles over others, what really matters most is consistency.

Big Chungus

10/15/2021, 1:33 PM

Apologies for the spam, but kon@1.1.0 is out with standardised setters and optional kontinx-serialization-json support for two-way conversions between

KON

and

JsonObject

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Matteo Mirk

10/15/2021, 3:10 PM

yeah this is better! When I saw all those different operators to perform the same action i was very confused

ephemient

10/15/2021, 8:30 PM

"array"[1]

in KObject may be an issue… what if you changed the DSL to

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kobj {
  "scalar" to 1
  "object".to { ... }
  "array".to[ ... ]
}

instead? seems more consistent to me

Big Chungus

10/15/2021, 9:37 PM

Why is String[] an issue? That extension is only available in kobject scope and hooks onto string class

Big Chungus

10/15/2021, 9:37 PM

Or do you mean string char accessor overlap?

Big Chungus

10/15/2021, 9:38 PM

I'll do some testing to see how relevant it actually is

ephemient

10/15/2021, 10:36 PM

yes, it'll resolve to String.get over your extension

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