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 <[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.
