module-import declaration

[David Alayachew]

In response to Rémi's point that no one wants this feature, I spent a lot
of time tutoring students who would frequently get tripped up on imports
and keeping track of them. This feature would have been a big help to
plenty of them back then. I understand that it has some pain points
(java.util.Date/java.sql.Date), but that's definitely not reason enough to
forgo this feature.

On Fri, Feb 23, 2024 at 12:41 PM Brian Goetz <brian.goetz at oracle.com> wrote:

> (I think we've had this discussion already?  Seems eerily familiar.)
>
> I realize that some people think star-imports are a bad idea, and some
> style guides recommend against it.  But these are preferences, which make
> sense in certain situations, and not in others.
>
> This argument goes: since star imports are bad, adding even more powerful
> star imports is definitely bad.  But the premise is flawed, so this
> argument does not hold.
>
> _The judge rules that "star imports are bad" arguments are inadmissible in
> this case._
>
> As a thought experiment, if we had modules from Java 1.0, would we have
> stopped at package-star imports and not module-star imports?  This seems
> unlikely.  Packages and modules are tools for grouping related classes,
> which are likely to be used together.  Saying "I want to use facility X" is
> an entirely reasonable thing.  Some facilities are packaged in a single
> package, so existing star-import works for them, but some are spread out
> over several packages that are almost always imported together (look at any
> "how to use Jackson" article, and you'll see that you have to import at
> least from jackson.core and jackson.databind to get much done.)  Arguably
> we should have added module-star imports in 9, but this was impractical
> given the constraints at the time.
>
> Turning to the "does it help beginners / simple programs" question,
> modules are a more sensible granularity of imports for simple programs.
> Such a program would prefer to say "I want to use Jackson", not "I want to
> use these three Jackson packages", or "I want to use these seventeen
> Jackson classes."
>
> As to the "onramp" angle, imports and packages are yet another
> program-structuring tool that benefits larger programs.  Having to learning
> them on day one is counterproductive.
>
> We know that import * has a bad behavior when upgrading dependencies, so hidding many import * behind a new import-module syntax means students will have to unlearn import-module later.
>
>
> (I think I've asked you before to keep away from the cheap
> high-school-debating tricks...)  This is a misuse of "unlearn".  Unlearning
> in this context refers to a dead-end convenience, which hides what is going
> on but can't be used for more than the simplest cases, and therefore has to
> be completely discarded and the user starts over.  (This is an onramp to
> the wrong highway.)  But this most surely isn't that.
>
> Users can progress smoothly from "implicit java.base import" -> "explicit
> java.base import" -> "explicit package import" -> "explicit class import"
> as the more fine-grained tools start to add value.  But I suspect it will
> be a long time for most users before they would ever have to go past module
> imports; seeing a list of module imports at the top is a pretty clear
> statement of what the classes dependencies are.  I don't see anything to
> unlearn here, ever; all I see is a simple form that can naturally be
> expanded to a fussier form as the specificity of the fussy form is needed,
> and which is revealed to be little more than said expansion.
>
> > Simple SQL examples with an "import java.sql.*" and a reference to a
> class "Date" to not compile anymore.
>
> Yes, it is unfortunate that there is this collision in java.base.  But
> this argument is not compelling; I have yet to see a program that imports
> java.sql.* that doesn't also import java.util.*.  So every user has to
> navigate this collision anyway.
>
>
>
>
>
> On 2/23/2024 4:56 AM, Remi Forax wrote:
>
> Hello,
> I've just read the draft of the third version of the implicit class JEP
>   https://openjdk.org/jeps/8323335
>
> There is a funny paragraph about why there is a need for an import module syntax.
>
> """
> One theme of this JEP is the elegant evolution of simple programs to proper declared classes that can reside in larger codebases; there is no beginners' dialect that must be translated away. In other words, it should be simple to evolve an implicitly declared class to an explicitly declared class. As implicitly declared classes automatically import (as needed) all the accessible classes and interfaces of every exported package in the module java.base, there should be a way to specify this in a traditional compilation unit with explicit class declarations.
>
> To this end, we add a new kind of import declaration: the module-import declaration. It imports (as needed) all the accessible classes and interfaces of every exported package in a given module.
> """
>
> So the thought process is: we do not want a dialect for beginners, but we want an import all, so we are introducing a feature nobody ask for, called module-import so look, this is not a dialect, this is an implicit import-module java.base.
>
> That's a funny !
>
>
> Taking a step back, I'm not sure that the idea of an "import all" is even a good idea.
>
> It makes the notion that classes are organized in packages hidden so the notion of package documentation (important for beginners) disappear.
> Simple SQL examples with an "import java.sql.*" and a reference to a class "Date" to not compile anymore.
> We know that import * has a bad behavior when upgrading dependencies, so hidding many import * behind a new import-module syntax means students will have to unlearn import-module later.
>
> regards,
> Rémi
>
>
>
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