Do we really need an implicit "import static java.io.IO.*"?
David Alayachew
davidalayachew at gmail.com
Sun Jun 2 04:05:34 UTC 2024
Well, I definitely see the discrepancy now. Yes, this makes a lot of sense.
Apologies for not recognizing your point earlier, I had assumed that you
were talking about some fundamental execution change that the kid needs to
be aware of. I didn't realize that you were talking about potholes that the
kid might fall into.
Long story short, you and I approach tutoring in WILDLY different ways.
First and foremost, the concept of introducing instance state this early on
is dangerous in my eyes. If you have a kid that can dance at that tempo,
then you truly have a gifted kid. But from my 10+ years of tutoring, EVERY
SINGLE TIME I try to introduce them to the idea of having state ANYWHERE
except for inside of a method, things fall apart. It will be a long time
before I ever try and get this kid to try and manage state at the instance
level.
I approach it very differently.
I start off teaching these kids to approach problems with a functional
mindset. Pure functions everywhere. This usually ends up creating a big,
singular essay of a function, and once they start to feel the strain from
that, I show them how to thread their state in through methods and return
values.
Anyways, back to my example from 2 emails ago.
Their JumboClassA is very big and unwieldy, and they want to use parts of
it for JumboClassB, and maybe other things I've introduced them to at that
point. If I haven't already, I introduce them to the Math class, show them
how it works, let them make a HelloWorld that does something meaningless,
let them call it in their existing class, let them call it in another
project, let them make a Math2, and then from there, they usually feel
comfortable enough to try and extract a method from what they were actually
doing into a pure, static function.
I have only tutored one student using this implicit class feature so far,
and we are nowhere near this point yet. But I expect that the only thing
that will change before I get there is explaining to them how, in order to
use their methods outside of the class, they need to give the class an
explicit name. I foresee no pain points with that. After all, how can you
reference a class that does not have an explicit name? And I expect them to
understand the unidirectionality of that. A class without a name can use
methods from a class WITH a name. But the reverse is false. I'm actually
sorted of excited to spring that onto the kids and see how they react lol.
Really, the only issue I ever run into is when kids ask me, what is static
useful for anyways? They usually feel like they only need static or
instance methods.
I guess what I am saying is that, since I don't really depend on static or
instance level state, I just don't have this problem. And by the time I do,
they have gotten so used to doing functional, that any interaction with
global state stands out as something to watch out for. From there, they
understand how much of an ordeal it is to work with state, and exactly how
dangerous and error-prone that it is that I can usually get them to turn
their alertness up to 11 whenever the need arises.
Let me first get your perspective though before I continue my point. What
are your thoughts on this?
And apologies for not responding to your points individually. Our
assumptions are on opposite ends, so there is very little that I can
directly respond to.
On Sat, Jun 1, 2024 at 11:22 PM Ethan McCue <ethan at mccue.dev> wrote:
> I really should find a better example / adapt something in an existing
> curriculum - but:
>
> Mutation 1: Make b static
>
> int count = 0;
>
> class A {
> static void b() {
> count++;
> c();
> new D();
> }
> }
>
> void c() {
> println("" + count);
> }
>
> class D {}
>
> void main() {
> new A().b();
> }
>
>
> https://run.mccue.dev/?runtime=latest&release=22&preview=enabled&gist=be416fe8e6df84c81c0f5526f0e28aef
>
> Mutation 2: Make c static
>
> int count = 0;
>
> class A {
> void b() {
> count++;
> c();
> new D();
> }
> }
>
> static void c() {
> println("" + count);
> }
>
> class D {}
>
> void main() {
> new A().b();
> }
>
>
> https://run.mccue.dev/?runtime=latest&release=22&preview=enabled&gist=b71e9b94cff6099afb5153abffdbc3e9
>
> Mutation 3: (for fun) Make A a record
>
> int count = 0;
>
> record A() {
> void b() {
> count++;
> c();
> new D();
> }
> }
>
> void c() {
> println("" + count);
> }
>
> class D {}
>
> void main() {
> new A().b();
> }
>
>
> https://run.mccue.dev/?runtime=latest&release=22&preview=enabled&gist=cb5bf4664bf83ffc8ee4e5fe85abadb6
>
> Maybe it's just a failure of imagination, but I don't know how to
> introduce static methods and fields into someone's arsenal without either
> * pulling the veil and explaining the anonymous class. This requires
> static imports. We've looped.
> * leaving them with guidance like "you can't make classes, records work
> though. I'll tell you later why. Just do math type stuff here."
>
> Then there is the confounding factor of *why* they would want a static
> method. In "real code" we use static methods and fields for
>
> * globals
> * "pure" logic
> * factory methods
>
> Before they move to another file, they already have globals and they can
> already put pure logic at the top level. Factory methods only make sense
> once you've introduced large program topics like visibility.
>
> I.E. you only need factory methods if
>
> 1. You want to hide a constructor
>
> class Point {
> private Point(int x, int y) {}
>
> static Point of(int x, int y) {
> return new Point(x, y);
> }
> }
>
> But this is a nuanced api topic and isn't even relevant when everything is
> a nestmate. Really a "large program" sort of choice.
>
> 2. You want to create through an interface
>
> interface LinkedList {
> int size();
>
> static LinkedList empty() {
> return new EmptyList();
> }
>
> static LinkedList notEmpty(int head, LinkedList tail) {
>
> }
> }
>
> class EmptyList implements LinkedList {
> @Override
> public int size() {
> return 0;
> }
> }
>
> But as you see from the code you need to have public to teach interfaces.
> You can gloss over it (my school did) but it's there. Even then "why not
> just new EmptyList()" has an answer really rooted in (again) large program
> concerns. You make code for potentially an external audience and need to
> give a "good" API.
>
> 3. You want otherwise incompatible overloads
>
> class Point {
> Point(int x, int y) {}
>
> static Point ofX(int x) {
> return new Point(x, 0);
> }
>
> static Point ofY(int y) {
> return new Point(0, y);
> }
> }
>
> Which does work a little. But it doesn't really give a good opener for
> static imports. The method names you'd give here are like ofX, fromX. You
> would want to use those qualified every time. You also activate the
> footguns I showed above.
>
> int pointsMade = 0;
>
> class Point {
> Point(int x, int y) {}
>
> static Point ofX(int x) {
> pointsMade++;
> return new Point(x, 0);
> }
>
> static Point ofY(int y) {
> pointsMade++;
> return new Point(0, y);
> }
> }
>
> --
>
> > I would always start by taking one of their projects, ask them to tweak
> in a subtle, but difficult way, then let them run headfirst into the
> problem. Once they start to feel the strain, I would introduce them to the
> concepts of classes.
>
> I think this is what I am missing. Without going into large or multi-file
> program design there isn't much reason to use static anything. *In
> addition* to that there are mechanical difficulties that can only be
> explained properly once you reach a 2nd file.
>
> I.E. - "you were actually using a class until now. For true globals use
> static fields", "For methods you can call anywhere use static" are the
> explanations I want to give. Both of those explanations need multiple files
> already in place to make sense.
>
> Does that track?
>
>
>
> On Sat, Jun 1, 2024 at 10:47 PM David Alayachew <davidalayachew at gmail.com>
> wrote:
>
>>
>> Heh, we're both unpaid :P I tutor folks from my university and church, as
>> well as a couple of friends and family. Slowing down now though because of
>> workload at work.
>>
>> But back to the point.
>>
>> > I think the problem is that without static "global"
>> > fields are always accessible and all the nested classes
>> > in their program are instansable from anywhere.
>> >
>> > Once you have a static method, a method on a record, a
>> > method on an enum, or a static inner class this is no
>> > longer the case.
>>
>> Apologies, maybe I missed the memo. I have been out of touch with this
>> (and all other JEP's) because of my insane workload for the past couple of
>> months.
>>
>> Why would adding a static method change any of the logic?
>>
>> I took your example in Java 22, added a static method, and everything
>> worked dandy.
>>
>> Am I missing something?
>>
>> On Sat, Jun 1, 2024 at 9:28 PM Ethan McCue <ethan at mccue.dev> wrote:
>>
>>> I am also basically just a tutor, just unpaid.
>>>
>>> I think the problem is that without static "global" fields are always
>>> accessible and all the nested classes in their program are instansable from
>>> anywhere.
>>>
>>> Once you have a static method, a method on a record, a method on an
>>> enum, or a static inner class this is no longer the case.
>>>
>>> Trite example of the mechanics I'm referencing:
>>>
>>> int count = 0;
>>>
>>> class A {
>>> void b() {
>>> count++;
>>> c();
>>> new D();
>>> }
>>> }
>>>
>>> void c() {
>>> println("" + count);
>>> }
>>>
>>> class D {}
>>>
>>> void main() {
>>> new A().b();
>>> }
>>>
>>> So when you show static methods, I think you need to understand why
>>> count++; and c(); and new D(); would not function.
>>>
>>> That requires knowing that you are actually in an anonymous class. That
>>> requires we get past import static java.io.IO. That's the loop.
>>>
>>>
>>>
>>> On Sat, Jun 1, 2024, 8:59 PM David Alayachew <davidalayachew at gmail.com>
>>> wrote:
>>>
>>>> Maybe I am missing something, but a static import seems like the
>>>> natural next step to teaching a student who made it that far.
>>>>
>>>> If a student feels the need to break out of the bounds of an implicitly
>>>> declared class, they must first understand what a class is going to save
>>>> them from. In this case, it is allowing code they right to be reused else
>>>> where.
>>>>
>>>> I am only a tutor, not a full-blown teacher, but when tutoring folks in
>>>> this exact subject, I would always start by taking one of their projects,
>>>> ask them to tweak in a subtle, but difficult way, then let them run
>>>> headfirst into the problem. Once they start to feel the strain, I would
>>>> introduce them to the concepts of classes.
>>>>
>>>> I would start by showing them how to create a simple pure function,
>>>> similar to java.lang.Math. From there, we would make a few pure functions
>>>> that are unrelated to their current task, and then have them get
>>>> comfortable with that concept.
>>>>
>>>> Then, we would make another pure function that is being done repeatedly
>>>> in their "JumboClass1" and "JumboClass2", and then have them get
>>>> comfortable using this helper method in both versions.
>>>>
>>>> In my mind, this is naturally where the student would discover that
>>>> they need to do a static import. In which case, they are in the middle of
>>>> understanding a class, they understand imports, and they understand static
>>>> methods fairly well. So, a static import has been well prepared for them.
>>>>
>>>> For me, this is a neat and clean introduction. Maybe I am missing
>>>> something?
>>>>
>>>> On Sat, Jun 1, 2024 at 6:43 PM Ron Pressler <ron.pressler at oracle.com>
>>>> wrote:
>>>>
>>>>> Hi.
>>>>>
>>>>> Without getting into the merits of not implicitly importing anything,
>>>>> let me just point out that the following is a valid program under the
>>>>> current JEP:
>>>>>
>>>>> void main() {
>>>>> IO.println(“Hello, world!”);
>>>>> }
>>>>>
>>>>> As is this one:
>>>>>
>>>>> import module java.base;
>>>>>
>>>>> void main() {
>>>>> IO.println(“Hello, world!”);
>>>>> }
>>>>>
>>>>> In other words, the fact that there are implicit imports doesn’t mean
>>>>> that you can’t ignore them or add them explicitly. if you find teaching
>>>>> this to be easier, you can. So even if you don’t find implicit imports
>>>>> helpful, they may be helpful to other teachers, who may not want to start
>>>>> with some import incantation that necessarily implies some
>>>>> programming-in-the-large concept.
>>>>>
>>>>> But I think that your unease mostly stems from the extra magic that
>>>>> implicit classes enjoy, and which isn’t strictly necessitated by their
>>>>> primary quality of being implicitly declared classes, and that extra magic
>>>>> differentiates them from regular compilation units along some other axis;
>>>>> is that right?
>>>>>
>>>>> — Ron
>>>>>
>>>>>
>>>>>
>>>>> > On 1 Jun 2024, at 23:14, Ethan McCue <ethan.mccue at lumanu.com> wrote:
>>>>> >
>>>>> > Hi all,
>>>>> >
>>>>> > I'm following the development of JEP 477[1] and I feel the need to
>>>>> question the impetus for the implicit static imports.
>>>>> >
>>>>> > As of now[2] any program like this
>>>>> >
>>>>> > void main() {
>>>>> > println("Hello, world");
>>>>> > }
>>>>> >
>>>>> > Is equivalent to
>>>>> >
>>>>> > import static java.io.IO.print;
>>>>> > import static java.io.IO.println;
>>>>> > import static java.io.IO.writeln;
>>>>> >
>>>>> > import module java.base;
>>>>> >
>>>>> > final class Main {
>>>>> > void main() {
>>>>> > println("Hello, world");
>>>>> > }
>>>>> > }
>>>>> >
>>>>> > Where all the methods in java.io.IO delegate to newly added
>>>>> equivalent methods in java.io.Console.[3]
>>>>> >
>>>>> > Aside from muddying that API up (now there is readln and readLine +
>>>>> println and printLine which...what) I'm still concerned on how those
>>>>> implicit imports will affect the transition to named classes.
>>>>> >
>>>>> > Assume we start a student out here
>>>>> >
>>>>> > void main() {
>>>>> > println("Hello, world");
>>>>> > }
>>>>> >
>>>>> > You can get through conditionals, loops, variables, methods, and
>>>>> return types before touching classes or access specifiers.
>>>>> >
>>>>> > int compute() {
>>>>> > int total = 0;
>>>>> > for (int i = 0; i < 10; i++) {
>>>>> > total += i;
>>>>> > }
>>>>> > return total;
>>>>> > }
>>>>> >
>>>>> > void main() {
>>>>> > println("Hello: " + compute());
>>>>> > }
>>>>> >
>>>>> > You can even talk about records and enums in a hand wavey way. Enums
>>>>> are "one of these options", Records are "if you want to return two things."
>>>>> >
>>>>> > enum Pirate {
>>>>> > BLACKBEARD,
>>>>> > OTHER
>>>>> > }
>>>>> >
>>>>> > record Pos(int x, int y) {}
>>>>> >
>>>>> > Pos treasure(Pirate pirate) {
>>>>> > switch (pirate) {
>>>>> > case BLACKBEARD ->
>>>>> > return new Pos(5, 5);
>>>>> > case OTHER ->
>>>>> > return new Pos(0, 0);
>>>>> > }
>>>>> > }
>>>>> >
>>>>> > void main() {
>>>>> > println(treasure(Pirate.OTHER));
>>>>> > }
>>>>> >
>>>>> > So it is reasonable for a student to have made a relatively complex
>>>>> program before having to get to that point, but I think you do need to
>>>>> explain what exactly is going on with the anonymous main class when you
>>>>> introduce multi file programs.
>>>>> >
>>>>> > As originally pitched, this transition would have just meant
>>>>> wrapping the whole program in class Main {}, but now to make the transition
>>>>> from
>>>>> >
>>>>> > void main() {
>>>>> > // Arbitrary code
>>>>> > }
>>>>> >
>>>>> > to
>>>>> >
>>>>> > class Main {
>>>>> > void main() {
>>>>> > // Arbitrary code
>>>>> > }
>>>>> > }
>>>>> >
>>>>> > In a robust way, you need to add those imports to the top. You can
>>>>> skip the final since the semantics of extension haven't been relevant yet.
>>>>> >
>>>>> > import static java.io.IO.*;
>>>>> >
>>>>> > import module java.base;
>>>>> >
>>>>> > class Main {
>>>>> > void main() {
>>>>> > // Arbitrary code
>>>>> > }
>>>>> > }
>>>>> >
>>>>> > My gripe is that the concepts introduced here - static, module, and
>>>>> * imports - would have had no place to be introduced earlier.
>>>>> >
>>>>> > If you have folks write static methods on inner classes, the
>>>>> metaphor of a "global field" that otherwise exists in the simple-main world
>>>>> goes away.
>>>>> >
>>>>> > // For every program up until this, they could freely access this
>>>>> from anywhere
>>>>> > int count = 0;
>>>>> >
>>>>> > // And they could freely make an instance of any inner class
>>>>> > class Other {}
>>>>> >
>>>>> > class Pos {
>>>>> > static Pos of(int x, int y) {
>>>>> > // So the rules they are used to don't apply anymore
>>>>> > // and the explanation as to why really lies *after* they
>>>>> understand
>>>>> > // what an anonymous main class is and does
>>>>> > // ...
>>>>> > }
>>>>> > }
>>>>> >
>>>>> > void main() {
>>>>> > // ...
>>>>> > }
>>>>> >
>>>>> > If you have folks *use* static methods that is fine - the
>>>>> hand-waving of Math.max doesn't seem to trip anyone up - but I can't figure
>>>>> out how to topologically sort topics such that import static makes any
>>>>> sense before going through multi-file programs.
>>>>> >
>>>>> > I have a similar concern with import module, but that can be hand
>>>>> waved as "gets you everything from this library" so I am less concerned.
>>>>> Still don't fully understand the desire to have it be implicit, but less
>>>>> concerned.
>>>>> >
>>>>> > Just as a hypothetical, say java.io.IO was java.lang.IO. No new
>>>>> import rules needed and now IO is available to all programs.
>>>>> >
>>>>> > void main() {
>>>>> > IO.printLine("Hello, world");
>>>>> > }
>>>>> >
>>>>> > While this does introduce something not explained - static method
>>>>> access - it feels easier to hand-wave away than import static java.io.IO.*;
>>>>> would be. It calls the printLine method, it comes from IO. IO means
>>>>> "Input/Output". That's a workable metaphor and can be glanced over in the
>>>>> same way as Math.max
>>>>> >
>>>>> > The transition from here to classes can again be "it's the same as
>>>>> if you had class Main {} around it" instead of "it's the same as if you had
>>>>> class Main {} around it and these imports. A static import imports a static
>>>>> method. A static method is a method attached to the class itself instead of
>>>>> the instance.... etc."
>>>>> >
>>>>> > Also, IO. feels like a different kind of unexplained boilerplate
>>>>> than public static void main(String[] args) {}. There is a lot of ground
>>>>> you need to cover before access modifiers, static methods, or command line
>>>>> arguments make any sort of sense. When you have someone write IO they are
>>>>> in that moment producing output and will soon take input.
>>>>> >
>>>>> > What am I overlooking?
>>>>> >
>>>>> >
>>>>> > [1]: https://openjdk.org/jeps/477
>>>>> > [2]:
>>>>> https://download.java.net/java/early_access/jdk23/docs/api/java.base/java/io/IO.html
>>>>> > [3]
>>>>> https://download.java.net/java/early_access/jdk23/docs/api/java.base/java/io/Console.html#print(java.lang.Object)
>>>>>
>>>>>
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