@hiredman :thumbsup::skin-tone-2:

Hello. Do you know any example about web push using clojure? I found the library ”web push-clojure” but I want to know any example about this.

In this code:

(def a ["a" "b" "c" "d" "e" "f" "g"])
(def b (assoc a 3 42))
(identical? (first a) (first b))
; => true

Does Clojure guarantee they'll be identical? Does Clojure's current impl of vector guarantee they'll be identical?

I guess what I wanted to ask is, does assoc'ing something onto a vector of size n produce something that always shares at least n-1 things with the original vector?

Or are there cases when less things are shared?

the values in the vector will all be identical except the one you replaced

what else could they be?

I'm not questioning whether assoc works. I'm wondering whether each leaf node in the HAMT has only one thing, and will never be copied as part of the path copying required to make the new vector.

If you are asking about the current implementation, it does not make copies of objects like that, that I am aware of. A counter-question for you: When would you care, except for performance?

I am not saying that performance is unimportant -- it definitely is important. It is just that if you are asking because you want to write code that relies upon things being identical? or not, I would advise against doing that, in most cases.

If you would like to explore some low level implementation details of Clojure data structures as they exist in memory, for Clojure on Java, there is this library I wrote that can help visualize the data sharing that occurs. In particular, the 'More example' section of the README has some sample code to color-highlight two HAMT's with different colors for data that is unique to one, or unique to the other, or shared: https://github.com/jafingerhut/cljol

Thanks!

I've made a JSON -> EDN tool and now someone asks about the case when you use key with spaces in JSON and keywordize them in EDN, you get something like this: {"foo bar": 1} -> {:foo bar 1} which is invalid EDN. I bet someone has thought of a solution regarding this before?

there are multiple solutions. one of them is to encode the space somehow, but it might not always that this is what users want

you could use string keys, or even emit (keyword "foo bar")

I guess edn/read would give you a useless list for that, so never mind

but that EDN should also be able to be read back in

right

string keys avoid the problem, at the cost of people not liking it

I outlined these solutions: https://github.com/borkdude/jet/issues/10#issuecomment-518123007

can transit handle a space in a keyword?

yes, it can

I suspect the best answer depends on the context and all of those possible solutions are best in some context

true

Unrepl has a solution to this

that makes me wonder, what do you do with EDN values that have no JSON representation? That is an equally destructive operation right?

Is there an easy way to call the constructor for a class that you have the value for at runtime?

I imagine I need clojure.reflect.

it might be easier to just use eval for something like that

clojure.lang.Reflector/invokeConstructor seems to do the trick, but I believe is internal.

"What are you trying to solve?"

there's no generic way to re-call a constructor for an arbitrary thing @zane

Great question.

I doubt you're working with arbitrary things, though

I'm trying to call the constructor for a class if it's available on the classpath.

I figured I'd use reflect/resolve-class to test for its presence.

so you have an object, then you get its class?

what if there are 5 constructors?

It's not an arbitrary class.

It's a specific class (`javafx.embed.swing.JFXPanel`) that may or may not be on the classpath depending on version of Java being used to run the program.

why not

user=> (if (try (Class/forName "Foo") (catch ClassNotFoundException _)) (eval '(Foo. x y)) :nope)
:nope

eval + delay

Yeah, eval would work for sure. I'm just wondering whether there's a better way.

You'd say that's preferable to Reflector/invokeConstructor?

yeah

Right on.

@zane does this help?

user=> (.newInstance (Class/forName "java.util.Date"))
#inst "2019-08-05T20:55:21.354-00:00"

(def my-thing (delay (eval '(some giant form))))

with conditionals around the argument to eval if you need 'em

only works with nullary constructors

.newInstance is deprecated

don't use it

good to know

(delay (eval (if (>jdk8?) '(jdk11 form) '(jdk8 form...))))

rather than checking a jdk version, it is much better to check for the existence of a class before using it

as that's much less likely to break than version checking

(having debugged my share of buggy java version check conditionals)

Does anyone know if you can type hint an argument of a type created by gen-class?

(gen-class :name model.Message) (defn some-func [^model.Message msg] ...)

Oh nevermind I guess I can, maybe this is better for cursive channel because it’s complaining that the class can’t be found… which makes sense since if it’s not compiled