[External] : Re: Feedback about LazyConstants API (JEP526)
Maurizio Cimadamore
maurizio.cimadamore at oracle.com
Tue Dec 9 15:18:33 UTC 2025
Hi David,
I think what you suggest is outside the scope of the LazyConstant API
(as Per has already said).
The goal of LazyConstant is to provide an easy to use abstraction for
lazy initialization that addresses the 90% use case (e.g. deferred
initialization using a lambda).
There will be another, more imperative API that can be used to build
what you want.
But what we have learned when working on this project, is that if we
increase the scope/reach of LazyConstant to include more imperative
aspects, it ends up with confusion pretty quickly.
The design you proposed was considered -- and rejected. While it holds
together, the fact that the initialization action provided at creation
acts now as a "fallback" initialization action, and can be overridden by
use sites calling computeIfAbsent was deemed surprising and/or confusing.
Regards
Maurizio
On 09/12/2025 14:46, david Grajales wrote:
> I am glad my feedback was helpful and sparkled such a great
> discussion. I would like to put 2 cents more, looking for these to be
> helpful.
>
> My main concern with "orElse" is that most of the time (at least for
> my how I would use this API in my job) most of the time I need a
> reliable way to set the constant and use that particular constant
> along the life cycle of the class, **not** declaring an alternative
> local variable in replacement because most of the time there is no
> good "burned in the code" alternatives that I could use . The use
> cases I have for this API are usually about deferred initialization of
> values that often require some time costly operation, some of those
> may involve calls to external services (IO operations) thus having a
> "burned" constant in these cases is not useful. Instead I propose a
> "computeIfAbsent" (I am not against orElse naming) method that allows
> for alternative downstream conditional initialization of the Lazy
> constant.
>
> private class Bar{
> LazyCosntan<Weather>weatherUrl = LazyCosntant.of(this::checkAndGetWeatherUrl);
>
> public Bar(){}
>
> private String checkAndGetWeatherUrl(){
> return Executors.newVirtualThreadPerTaskExecutor()
> .submit(() ->/*Some query to check if the weather server is up*/);
> }
>
> private String checkAndGetAltWeatherUrl(){
> return Executors.newVirtualThreadPerTaskExecutor()
> .submit(() ->/*Some query to check if the alt weather server is up*/);
> }
>
> public WeathergetWeather(){
>
> var url =weatherUrl.computeIfAbsent(this::checkAndGetAltWeatherUrl).get();
> // logic to get the weather here using the lazy constants// }
> public voidsendWeather(){
> var url =weatherUrl.computeIfAbsent(this::checkAndGetAltWeatherUrl).get();
> Executors.newVirtualThreadPerTaskExecutor()
> .submit(() ->/*Send the weather url to somewhere else* using weatherUrl*/);
> }
> }
>
> This pattern is very common, either for a trivial weather or to check
> or a conf and alternatives in case the regular one is not available
> (for example a conf file that may be missing and one may set a method
> that downloads it from a remote server first in case it is absent)
>
> So for me the issue is not the concept of "orElse" but how the current
> implementation returns me an alternative value instead of SETTING an
> alternative value in case the regular attempt fails or hasn't been
> called still because the program followed an alternative path before
> the obvious regular initialization path. If the orElse (or any other
> name that fits) changes the behaviour to set a value instead of
> returning something it would be the best approach IMHO.
>
>
>
>
> El mar, 9 dic 2025 a la(s) 9:13 a.m., Anatoly Kupriyanov
> (kan.izh at gmail.com) escribió:
>
> My idea is not an optional /interface/, but an interface for
> something which is convertible to the Optional /type/. In other
> words, neither the LazyConstant nor to ScopedVariable *is not* an
> optional itself, but could be converted to it uniformly.
> Something like this:
>
> interface Optionable<T> {// need to think about the better naming!
> T orElse(T other);
>
> // and maybe even:
> default Optional<T> asOptional() {
> return Optional.ofNullable(this.orElse(null));
> };
> }
>
> and then LazyConstant, ScopedVariable, etc could just implement
> the interface to unify on the notion of "return a user-provided value
> if some condition isn't met". Sounds like a decent path to abolish
> nulls.
>
> But I feel I am overthinking this...
>
>
> On Tue, 9 Dec 2025 at 13:35, Red IO <redio.development at gmail.com>
> wrote:
>
> I initially thought I agree with your statement that orElse is
> a common pattern in the jdk. But then I failed to come up with
> a second example. I then searched the jdk github repo for the
> method. And I only found Optional and it's specializations and
> ClassHierarchyResolver.
> So I would suggest yes, it's an often used method ... of the
> Optional class. Not many apis seem to expose it. The case of
> exposing an accessor that returns an Optional on the other
> hand is incredibly common across the jdk. This is exactly the
> case Optional was designed for. In this sense Optional is the
> "Interface" you are suggesting.
>
> My main argument against reusing orElse here is that the
> context is a completely different one.
> An Optional orElse method is a pure function that always
> returns the same value. It signals that the value is not there.
> LazyConstant is different in this regard. The LazyConstant
> orElse is not pure at all. It depends on rather someone else
> already initialized the value or not. It signals that the
> value is not there YET.
>
> Great regards
> RedIODev
>
>
>
> On Tue, Dec 9, 2025, 13:51 Anatoly Kupriyanov
> <kan.izh at gmail.com> wrote:
>
> Right, the ScopedValue is another good example I've
> forgotten. In that case I am even more inclined to keep
> the `orElse` as it looks like a repeating pattern across
> JDK libraries. Consistency is the way to go!
> And maybe even consider having a new interface for the
> method to make this pattern explicit?..
>
> I am glad that `orElseSet` is removed, the side-effecting
> is bad; also in other parts of JDK we already have
> `computeIfAbsent` for the same idea. I did not hear about
> it, and yeah, sounds like the source of this confusion.
>
>
> On Tue, 9 Dec 2025 at 12:05, Maurizio Cimadamore
> <maurizio.cimadamore at oracle.com> wrote:
>
>
> On 09/12/2025 11:59, Anatoly Kupriyanov wrote:
> > To be honest, I don't really see why this method
> causes such confusion.
>
> In part I agree. E.g. when we added this, what we had
> in mind was just
>
> https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/ScopedValue.html#orElse(T)
>
> E.g. other APIs have `orElse` method that return a
> user-provided value
> if some condition isn't met.
>
> I believe the problem we're discussing here is likely
> also related to
> the fact that the API used to have a side-effecting
> `orElseSet`, which
> is now removed, and I wonder if, because of that,
> folks are reading too
> much into what orElse does?
>
> Maurizio
>
>
>
> --
> WBR, Anatoly.
>
>
>
> --
> WBR, Anatoly.
>
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