How to get the class of a generic at runtime?

[chilly vault]

<@&1004656351647117403> please have a look, thanks.

[reef narwhal]

Title really should be "How do I use hibernate with generics"

not interested in rewriting this dao and repo pattern for every class I have

[rotund sierra]

short answer: you can't

[reef narwhal]

D:

why?

[reef narwhal]

Is there a way to do this with generics?

Or am I going to have to copy and paste for all of my entities

it's 4 files for every one entity

it'd be really nice if I could just have one file that implements the only thing that's different between all of them

[pine sage]

yeah

gimmie a sec i'll write you a demo

[rotund sierra]

because generics only exist at compile time
there is an exception tho

[pine sage]

import java.lang.reflect.ParameterizedType;

abstract class BaseClass<T> {
    final Class<T> param;
    BaseClass() {
        param = (Class<T>) ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }
}

class Apple extends BaseClass<String> {

}

void main() {
    var a = new Apple();
    IO.println(a.param);
}

param = (Class<T>) ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments()[0];

lots of assumptions baked into this line

but as you see, we do preserve generic info with extension

[reef narwhal]

I found that solution online

and ow

[pine sage]

i know, i am talking to you online

[reef narwhal]

I meant stack overflow :p

It's just...nasty

what is that

[pine sage]

there are multiple answers to that

[reef narwhal]

what assumptions?

[reef narwhal]

yeah, exactly, so it can get the class type, right?

i don't understand how classes are handled in java

[pine sage]

would you prefer

• The historical answer, where we blame it on compatibility
• The "measured" answer where we go through the alternatives to erasure
• Something else

[reef narwhal]

I'd prefer java to not need classes up my ass and out my eyes D:

(I am coming from C++ primarily)

[pine sage]

• that the class is only being extended once - otherwise this.getClass().getGenericSuperclass() might not be BaseClass
• That the type arguments are supplied
• That the type argument is a class and not itself another generic

[reef narwhal]

those are true for this case

so I think it will work

[pine sage]

which means the assumptions hold

you can make checks to ensure they do - which might be helpful since you can provide better errors

[pine sage]

there is good and bad news

the bad news is that the JVM deals in classfiles. You gonna have classes.

the good news is that if you write this

public final class Fruits {
    private Fruits() {}
}

then the class is essentially just a namespace for functions

public final class Fruits {
    private Fruits() {}

    public static void eat(/* ... */) {
        // ...
    }
}

Fruits.eat(...);

[reef narwhal]

this is just for a class assignment, i'm not worried about it after this class

the ship just needs to get to shore 🫡

[pine sage]

and a lot of stuff - like public everywhere - are borne out of monkey see monkey do more often than legitimate need

[reef narwhal]

yeah, that's the part that is really really wack coming from C

C/C++ have plenty of issues, but I've stepped on enough of their piles of glass that I know where not to step lol

gotta go through the same process with Java

[pine sage]

there are languages based on the JVM which genuinely just have functions

[reef narwhal]

I've heard good things about Kotlin

[pine sage]

so the fact that its classfiles under the hood isn't that important

[reef narwhal]

No, I mean, it's turing complete and it's not super obnoxious, it's just one of those things that is more annoying to deal with in Java than C++ which is rare

you can make spaghetti monsters of six different function calls that all resolve at compile time in C++

I've fucked myself way harder with templates in C++

[pine sage]

my opinion on kotlin is that when it came out it was much better than Java. It had many things Java didn't have. Nowadays Java has 80% caught up and kotlin hasn't really kept up + some of the things unique to kotlin actually are net negatives

so i sorta don't care - but yeah they do have package level functions

[reef narwhal]

As Stroustrup said, "There are the languages that people complain about and the languages people don't use"

[pine sage]

yeah you'll have a simpler life in java

it can certainly get insane, but in a different way than c++

and you're in the same ballpark speedwise for most things

the original target audience for Java was legitimately C++ developers - you can see it in documentation, marketing, etc.

[reef narwhal]

Alright well I gave up on generics

going to be easier to copy and paste 36 files than deal with Java generics

[pine sage]

yeah life advice - just write the code

not related to java generics even, just a thing

[reef narwhal]

not really sure what that means

i'm writing the code? I just was trying to make life easier

it was worth a shot

just calling it quits because the investment is no longer worth the outcome

[reef narwhal]

please elaborate

I'm also not really writing code, just refactoring by hand

and copy pasting

[pine sage]

there are a lot of ways to "be smart" in programming

[reef narwhal]

that's why i reached for generics

[pine sage]

some of these work out

some don't

but the dumbest possible solution will often work - like just copy pasting the code

and you know how long it will take

[reef narwhal]

I don't midn doing it a few times, but I am not kidding when I say I have to copy past 36 different files

I always say at work, "sometimes you gotta earn your check"

chores suck 😩

[pine sage]

a key insight is that, no matter what, writing code takes up a lot less of your time than reading code

which isn't true for an assignment but is true for real code and real software

[reef narwhal]

oh yeah, i worked in dolphin (open source game cube emulator) and writing code was such a minimal part of that project lol

you can just fuck yourself by making it hard to read

so hope you don't ever have to extend it

[pine sage]

so if you do something that makes it easier to write the code (like what you were thinking with the generics) but makes it more complicated/harder to read/spreads out logic - that is often a net negative

[reef narwhal]

oh i see what you're saying

that's a good point

huh

hadn't thought of it like that before

sometimes a 300 line switch statement is the way to handle all of the dialogue in a game

(sorry, that's how undertale did his dialogue. I realize that might not be common knowledge)

[pine sage]

its actually a common thing for "popular video game DESTROYED" for people to look at code that is like a 10,000 line function and go "eww bad"

but you know what? pretty simple and you aren't looking at all 10,000 lines at once

[reef narwhal]

true, but unless you know what you're looking for, you have to scroll through all of it

[pine sage]

correct. and that matters more on larger teams than smaller ones

[reef narwhal]

idk, the more things i do and make professionally (in manufacturing and software) the more I realize the answer to "what's the best way to do this?" is rarely a relevant question

"what will get this done by the due date?" is a much more relevant question

[pine sage]

but you can never escape needing to write code for other people to read

since you of a month from now is meaningfully different than the you of today

[reef narwhal]

a month?

try an hour

lol

[pine sage]

okay dumbass

most of us ship of theseus slower

but you get what I mean

there is a cost that you pay later for abstraction and indirection

[pine sage]

this where "tech debt" comes from

you make a choice that helps you today but gets in the way of what you want to do tomorrow. It is unavoidable to end up with some in the presence of any deadlines

its not intrinsically good or bad

[reef narwhal]

oh 🙁

i was just making a self-deprecating joke

my memory is pretty bad

and it gets worse the more i use it in a day

[pine sage]

i know