Re: GEP-16: val keyword for final declarations
MG <mgbiz-yvYIh6MZAuFWk0Htik3J/[email protected]> Tue, 14 Apr 2026 23:49:28 +0200
| Newsgroups | gmane.comp.lang.groovy.devel |
|---|---|
| Message-ID | <[email protected]> |
Hi Paul,
1. Is the plan then for "final" to be the same as "val" with regards to
type inference, because that would mean we can actually ignore
"val", otherwise we at least will be forced to use it in our framework ?
2. Same question for "var": Will it also use the same type inference as
"val", and no longer just be an alias for "def" ?
Cheers,
mg
PS: We use Groovy only in our team, and all of our method return types
are explicit, we only use def in the extremely rare case a method
returns a anonymous class instance.
Am 14.04.2026 um 22:31 schrieb Paul King:
> It is not really about copy-n-paste of Kotlin code. It is about Groovy
> feeling like a comfortable language to use for folks from different
> backgrounds and teams that work in multiple languages.
>
> Usage of "var" and "val" is totally optional.
>
> Some teams might be Groovy to the core and have CodeNarc rules
> forbidding "var" and "val". That's okay.
>
> Other teams that also work a lot with Kotlin or Scala, might always
> use "var" and "val" and always explicitly type their method return
> types (no "def" anywhere). That's okay too.
>
> Cheers, Paul.
>
> On Wed, Apr 15, 2026 at 5:38 AM MG <mgbiz-yvYIh6MZAuFWk0Htik3J/[email protected]> wrote:
>
> Hi Gianluca,
>
> I agree:
>
> 1. I would say people copy & paste from Java, since there is so
> much code out there /and/ since Groovy (I think rightly so)
> has always tried very hard to stay syntax compatible with it.
> 2. Kotlin is imho too different for one keyword to make much of a
> difference - just think e.g. of its JavaScript-style postfix
> type syntax - and JetBrains offers only Groovy-to-Kotlin
> autoconversion in IntelliJ, for obvious reasons.
> 3. Scala uses the same type syntax, is less popular, as well as
> more functional than Groovy, so there is even less argument to
> be made here to have a small copy & paste compatibility.
>
> Cheers,
> mg
>
>
> Am 14.04.2026 um 09:52 schrieb Gianluca Sartori:
>>
>> > It's a convenience to have some more copy/pasting friendliness
>> with languages that adopted val.
>>
>> Is this a real case? Do people copy paste from Java/Scala/Kotlin
>> into a Groovy file/project?
>>
>>
>> Also, raising the topic to a philosophical layer, sometimes
>> adding features dilutes the concepts.
>> I'd rather prefer to have a strong language with few concepts and
>> its own identity.
>>
>> When we want to please anyone, we end up pleasing no one.
>>
>> I also believe we should start thinking about a Groovy version in
>> the future (like version 10 for instance) where we make breaking
>> changes to consolidate the language (like Python has done in
>> version 3).
>> Breaking changes are painful, risky and always too much work, but
>> as with any other software the issue is "when" not "if".
>>
>> Mantra of the day:
>>
>> To add is simple,
>> to remove is complicated.
>>
>> Sorry if this sounds a bit critical, my intention is to be helpful.
>>
>> Gianluca Sartori
>> --
>> https://dueuno.com
>>
>>
>> On Tue, 14 Apr 2026 at 08:32, Guillaume Laforge
>> <[email protected]> wrote:
>>
>> We also have var although we had def.
>> It's a convenience to have some more copy/pasting
>> friendliness with languages that adopted val.
>>
>> On Tue, Apr 14, 2026 at 12:30 AM MG <mgbiz-yvYIh6MZAuFWk0Htik3J/[email protected]> wrote:
>>
>> Hi Caleb,
>>
>> my main argument is that one does not need "val", if
>> already existing "final" would do the same thing, i.e. do
>> RHS type inference (see also "To add to my initial
>> arguments" in my reply to Christopher Smith).
>>
>> Cheers,
>> mg
>>
>> PS: To comment on some of your points:
>>
>> 1. One does not always have the luxury of using an IDE
>> when looking at Groovy code.
>> 2. A simple syntax highlighting editor (if that is
>> available) might struggle with separating "val" the
>> keyword from "val" the variable/field name (one of
>> the many reasons why I think "val" is such a bad choice).
>> 3. @any declaration that takes multiple words: True for
>> most ppl, full agreement, but we can use existing
>> single word "final" keyword (or, if necessary,
>> introduce a better one than "val"), as in final x =
>> new Foo().
>> 4. @value-based semantics never having been a thing in
>> any JVM languages: It is in Groovy, see @Immutable*
>> (which GEP-16 explicitly states of being a non-goal
>> of introducing a "val" keyword).
>>
>> *https://docs.groovy-lang.org/latest/html/gapi/groovy/transform/Immutable.html
>>
>>
>> Am 13.04.2026 um 02:23 schrieb Caleb:
>>> MG,
>>>
>>> A note on "val" looking similar to "var": any good IDE
>>> labels final and non-final variables differently, e.g.
>>> IJ uses an underline. Even vim does this afaik. The
>>> keywords look similar in isolation, sure, but everywhere
>>> besides the declaration, you're not looking at the
>>> keyword for that info. And with the underline on the
>>> variable, the declarations don't look similar at all
>>> from experience. I've never been confused in Kotlin,
>>> even coming from Java where var was the only similar
>>> keyword.
>>>
>>> Plus, from my experience, any declaration that takes
>>> multiple words to communicate it (even something as
>>> small as "let mut") just feels clunky compared to "val"
>>> and "var". It doesn't feel good to use, as it takes up
>>> more space in your brain trying to read it.
>>>
>>> You're also intuitively dissuaded from using the more
>>> complicated one because it takes an extra word, so if
>>> "final" is the extra word and it's not necessary to
>>> basic operation, very few people will use it. (See:
>>> Java, C, C++, literally every single language where
>>> "final" is the "second word".)
>>>
>>> On the topic of val meaning value-based semantics:
>>> that's never been a thing in any JVM languages, and val
>>> isn't used as a keyword in the major languages where it
>>> does exist. (Namely C, C++, and Rust.)
>>>
>>> Cheers,
>>> Caleb
>>>
>>> On Sun, Apr 12, 2026, 6:35 PM MG <mgbiz-yvYIh6MZAuFWk0Htik3J/[email protected]> wrote:
>>>
>>> Hi Paul,
>>>
>>> I still have the following gripes with using "val"
>>> (and two other languages having imho made a bad
>>> choice here still does not change that :-) ):
>>>
>>> 1. "val" for me indicates value- (as opposed to
>>> reference) based semantics, i.e. copy semantics
>>> / deep immutabilty, which the proposal explictly
>>> states is not the goal here (see Non-goals
>>> @Immutable in the GEP).
>>> 2. "val" looks a lot like "var".
>>> 1. So if looking over code it is harder to spot
>>> an error in this regard
>>> 2. And it might be confusing for ppl new to
>>> Groovy (unless they come from Kotlin or
>>> Scala, which I find unlikely to happen).
>>> 3. "val" is a variable name ppl use (Contrary to
>>> final, def and var).
>>> 1. While this would still work , e.g. "val val"
>>> just looks akward.
>>> 2. As well as making code using "val" as a
>>> variable name generally worse to read.
>>> 4. I see no need for "val", when it seems the same
>>> effect could be reached by changing the
>>> semantics of existing "final" to use RHS type
>>> deduction*.
>>> 1. It seems to me this would not be a breaking
>>> change... (?)
>>> 5. So while having type deduction would help our
>>> framework quite a bit, I would argue for:
>>> 1. "final" to finally be type deducing* G-)
>>> 2. Or at least for a different keyword to be used.
>>> 1. It is late and I need to go to sleep,
>>> but from the top of my head: "fvar" or "fin"
>>> 1. ("fin" would hit two birds with one
>>> stone: shorten the quite long
>>> "final" and supply type deduction).
>>>
>>> Cheers,
>>> mg
>>>
>>> *straightforward & stable, i.e. 99% what the user
>>> expects - make the frequent case easy/fast, make the
>>> rare case correct (i.e. require the developer to
>>> supply an explicit type).
>>>
>>>
>>>
>>> Am 12.04.2026 um 13:59 schrieb Paul King:
>>>> Hi folks,
>>>>
>>>> We have been asked numerous times about the
>>>> possibility of having a "val" keyword to match
>>>> Kotlin and Scala. We also have had a related Jira
>>>> open for more than 6 years. So I created a GEP to
>>>> help frame a discussion about what would be
>>>> involved and help us make a decision:
>>>>
>>>> https://groovy.apache.org/wiki/GEP-16.html
>>>>
>>>> I know we have "final", but many developers I speak
>>>> to from the Kotlin and Scala worlds are big fans of
>>>> "val" and believe it was the right name to use for
>>>> those two languages.
>>>>
>>>> Given that it involves changes to only about 15
>>>> lines of production Groovy code and has
>>>> well-identified impacts (arguably edge cases with
>>>> workarounds), I am largely in favor of this
>>>> proposal, but I am keen to hear other's thoughts.
>>>>
>>>> Cheers, Paul.
>>>>
>>>>
>>>
>>
>>
>>
>> --
>> *Guillaume Laforge*
>> Apache Groovy committer*
>> *
>> Developer Advocate @ Google Cloud <https://cloud.google.com/>
>>
>> * Blog: glaforge.dev <http://glaforge.dev/>
>> * X: @glaforge <http://twitter.com/glaforge>
>> * Bluesky: @glaforge.dev
>> <https://bsky.app/profile/glaforge.dev>
>> * Mastodon: @[email protected] <http://%[email protected]/>
>>
>