module-import declaration

[Brian Goetz]

(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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