The Nineteenth Byte

Ginger

20:00

I have a class that looks like abstract class NodeVisitor<N: Node<N>, R> and has lots of functions that take N and return R

Seggan

why is N recursive

Ginger

I want each function to be able to return a different subclass of N, but currently they can all only return N itself

@Seggan because it made the errors go away :p

/srs that's the type of the child

Unrelated String

ahh

Ginger

a Node<N> can only have children of type N, and I want it to only have its own type as its children

I've made a type that's its own parent and child :b

it's like Time Travel 101 all over again

2

Seggan

why not just N : Node<*>

Ginger

20:03

lemme try it

because that causes errors

Seggan

how

what errors

Ginger

protected fun visit(node: N): R {
    return node.accept(this)
}

that errors with Type mismatch: inferred type is NodeVisitor<N, R> but Nothing was expected

regardless, that's not the problem I want solved

Seggan

@Ginger ah yes because the compiler doesnt know the type it wants accepted

your only solution is to break the recursion i think

Unrelated String

Nothing was expected

sounds like kotlin needs to get some higher standards :P

Ginger

the recursion is a. intentional and b. not the issue I want solved

Rydwolf Programs

20:08

@Ginger Ooh a protected fun visit! Like a field trip!

Seggan

Time Travel 101 has field trips?

Ginger

:D

@Seggan yeah, at the end of every year we go back to the start of class so we can laugh at how stupid our past selves were

it's great

Seggan

@Ginger hrm but according to oop you should be able to return a subclass for a superclass, no?

Ginger

@Seggan yes

but if I hover over the declaration it says that N is being replaced with UntypedNode at compile-time

I want it to be left generic

Unrelated String

presumably what you're really looking for is specializing the generic multiple different ways?

Ginger

20:12

yes, probably

Seggan

@Ginger yes, because type erasure

Ginger

can I keep it from being erased?

Seggan

the jvm does not keep generic type information

@Ginger only by using inline classes

but those are quite limited

Ginger

or do something to signify that the return type can be any subclass of N?

@Seggan tell me more...

Seggan

@Ginger the return type is N, which by oop can also be any subclass

Ginger

20:15

oh yikes you weren't kidding about them being limited

Seggan

actually reified generics dont even work with inline classes

only inline functions

Ginger

is there any way to make this work???

because I will be much sad if I have to put casts everywhere

Seggan

2 mins ago, by Seggan

@Ginger the return type is N, which by oop can also be any subclass

Ginger

but it no worky

Seggan

well, ig its a good thing Time Travel 101 warns you about the fact that the universe hates time travel

(did it? mine did)

Ginger

20:19

it did

Seggan

@Ginger kotlinlang.org/docs/inline-classes.html

DLosc

20:39

@Seggan Indeed

user

@Seggan wdym

We time travel all the time

Can't control where you travel but you travel ;P

Seggan

20:53

@user i meant to the past

Time Travel 101

51 mins ago, 51 minutes total – 51 messages, 6 users, 1 star

Bookmarked 5 secs ago by Seggan

user

A message a minute, nice

Jacob

im still in pre-time travel

we do simulations in cardboard boxes

Bbrk24

For some reason I found myself attempting to implement the fixed-point combinator using C++ templates. ~~Knowing how C++ templates are abused, that probably already exists...~~

Seggan

6

Q: Fixed point combinator in C++1x

This has been tested and compiled under Visual Studio 2010. Are there any serious problems with this implementation? PS. This implementation is fully lambda expression based. If I can make fixpoint::fix a real member function it will be simpler than this. //As decltype(variable)::member_name is...

Bbrk24

21:08

No, that uses operator(), I meant something like

template<class T>
struct y {
   using type = T<y<T>::type>;
};

But I imagine that's not legal as written

Ginger

ಠ_ಠ

Bbrk24

The motivation I had for this isn't even a good one

template<class T>
class foo : public T {};

foo<foo> // Wait, you can't do that...

template<class T>
struct y {
   using type = T<y<T>::type>;
};

y<foo>::type // infinite recursion much?

To be clear, that first class declaration is legal C++

Ginger

21:51

okay, in theory Rabbit should be functional now

in theory

oh wait nvm I forgot a bit

ATaco

Woot, I fixed my memory leak and now have a scrolling bitmap!

C really will just let you footgun yourself on every turn, huh?

Bbrk24

Why does my binary size change by ~500 bytes when I reorder some enum cases

ATaco

Compilers are magic

Ginger

well

I did it

let's see if it runs

Bbrk24

Like, if it made a little difference because it figured out some bitwise magic, I would understand that. But 500B is more than I expected

Ginger

22:05

me when build failed

nice, we got a successful compile

time for run

history is about to made

Bbrk24

Oh! I figured it out! When I reordered my cases, it reduced one function from a long switch statement to arg ^ 1 and another to arg & 2 ? arg : arg ^ 4.

Ginger

you'll never guess what happened

it crashed

oh, I named my main function main (a keyword) :/

crashed again because I tried to cast an UntypedFunctionDeclaration to an UntypedStatements somehow

I forgot to remove a test cast :|

> Exception in thread "main" java.lang.IllegalStateException: ?!

thanks past Ginger, very cool

Bbrk24

~~I told you, it's TRUE, not true.~~

Seggan

@ATaco C is glorified assembly language

ATaco

Haha no overhead go BRRRRRRR

DLosc

22:20

@ATaco Sometimes you really need to get your shoe off and a gun is the only tool you have

If you aim very carefully, you won't hurt yourself :P

(This sounds like a scene from a cheesy action movie, TBH--one of the kind where someone loses a limb and attaches a gun as a prosthesis)

ATaco

Guns Akimbo, staring Daniel Radcliff

He gets kidnapped and guns affixed to his hands.

Seggan

@ATaco thats why c++ is bad. it tries to add GP stuff to glorified assembly language

and it fails at that mixture horribly

DLosc

@ATaco That, or I think the Quentin Tarantino movie Grindhouse has a woman with an automatic rifle for a leg. (Not that I've watched either movie.)

ATaco

I do not like C++, too many librarys :(

Ginger

@Seggan how do I check if a Kotlin object is a subclass of a type? is doesn't seem to work

DLosc

22:26

@Seggan That's... a really succinct and coherent argument, actually. I'll have to remember that one.

Seggan

GP as in general purpose

@Ginger a is WhateverClass?

i dont see why it wouldnt work

Ginger

oh wait nvm lol

I am square brain

AAAAGH it almost worked!

Seggan

@DLosc i wonder how rust managed to do it though

i think its bc they started with simple GP features and added the low level stuff, rather than the other way around

Ginger

@Seggan how do I get a HashMap to return the same value for two different instances of an inline class?

(their values are the same ofc)

← 2 messages moved from Vyxal

lyxal

(for context, I approved the above)

Ginger

22:38

cool

Seggan

@Ginger why are you using inline classes?

Ginger

because it is what it is

user

@Ginger Make two copy or box it

Ginger

~~don't ask questions just provide answers~~

user

m[k1] = v; m[k2] = v

Exactly the same as you would do in other languages

Seggan

22:40

also i think you can just override equals if i understand ur q

Ginger

@Seggan yeah probably, how do I do that?

Seggan

@Ginger those are for extraordinary use cases

@Ginger ...

Ginger

I'm an extraordinary kinda person

Seggan

im quite sure you know how to override a method

Ginger

ohhh right lol

was confused

@Seggan doesn't work

@Seggan I think I can fix it by overriding hashCode(), but the problem is that that also differs between strings (I think)

okay what in the frick

it doesn't, so why isn't this working?!

Seggan

22:48

@Ginger no it doesnt

and yes you have to override hashcode too

Ginger

wait, I have to do both???

Seggan

yes

hashmaps search by hashcodes first

Ginger

still doesn't work

Seggan

code?

Ginger

my logs indicate that equals isn't called either

class Identifier(val name: String) {
    override fun toString(): String {
        return name
    }
    override operator fun equals(other: Any?): Boolean {
        return name.equals(other)
    }
    override fun hashCode(): Int {
        return name.hashCode()
    }
}

@Seggan ^

Seggan

22:52

first, thats not an inline class

second, equals is not implemented improperly

think about it

Ginger

@Seggan I know, Kotlin doesn't let inline classes override hashCode or equals

Seggan

mhm

Ginger

@Seggan I may be stupid

Seggan

*not

what does identA == identB eventually turn into?

Ginger

wait, if I add a println to equals it doesn't get called

Seggan

22:54

identA.equals(identB) -> identA.name.equals(identB) see the error?

Ginger

ohhhhhhhhhhhhhhhhhhh

regardless, equals isn't called at any point

Seggan

thats abnormal

can i see the map code?

Ginger

could you be more specific? I've got lots of map code :p

Seggan

as in the code you need help with

Ginger

fun get(key: Identifier): RabbitObject {
    return this.variables.getOrDefault(key, this.parent?.get(key) ?: error("No such key $key"))
}

DLosc

22:57

@Ginger I feel like this live debugging chat is getting to be a bit too much. Would you mind creating a Kotlin room and moving it there?

Ginger

@DLosc I would, because it's very much on-topic here

it's "general discussion", so I think programming talk counts as on-topic discussion

also, nobody's discussing anything else

regardless: @Seggan that's the code causing the error

lyxal

@DLosc be glad you weren't around for the two hours of explaining linear interpolation yesterday then :p

Seggan

@Ginger have you checked the contents of the maps?

use a debugger, for codes sake

Ginger

@Seggan my debugger is crap and doesn't work properly

but I know for a fact that the map (at the point where it errors) contains an Identifier containing the string print

I also know for a fact that that's what's being passed to the get function

uh, I just checked and the hash codes are exactly the same

something else must be going on

DLosc

@lyxal I wouldn't have minded that because it's a topic I find interesting, but if someone had suggested moving it to a different room I would 100% have agreed

Seggan

23:15

@Ginger try manually invoking equals

@Ginger print them

Ginger

@Seggan {print=community.rto.ginger.rabbit.interpreter.WrappedFunctionDeclaration@52f759d7}

@Seggan it says they're equal

DLosc

@lyxal I'm reading the transcript now and it's a wild ride X^D

lyxal

@DLosc as I said, be glad :p

Seggan

@Ginger i found whats wrong

Ginger

oh boy

Seggan

23:22

getOrDefault has to evaluate both args before getting

you follow?

Ginger

I KNEW IT

I was sure it was an issue with that

Seggan

i think kotlin has one with a lambda that is evaluated only on null

ig you can turn it back into an inline class now :P

or you can use elvis

Ginger

I am using elvis

Seggan

this.variables[key] ?: (this.parent?.get(key) ?: error("No such key $key"))

Ginger

ohhhhhhhhh

Seggan

23:31

works?

Ginger

having tech issues

Time Travel 101

Transcript for