Reading on the web for clojure polymorphism, there is a statement which says use multimetods when you really need them otherwise you just protocols

Do you agree on this in a general manner? Or what is your experience with this, just for curiosity sake 🍶

multimethods are the devil, they can take your nice functions and smear it across several namespaces and change them on import, but sometimes thats what you want (they are also pretty hard to manipulate in the repl)

in general you want to use the most specific/least general abstraction at hand imo, multimethods are extremely open and protocols are contained

protocols are just as open as multimethods

As much I read, multimetods are less performant then protocols. And they dispatch on a multiples values rather then protocols where you have your type dispatch

that's true, they are less performant than protocols if you're only measuring method call dispatch and not the work done by the body of the multimethod

Don’t fear multimethod perf - the overhead might be 70 ns vs 15 ns for protocol calls. Yes, that’s more, but probably dwarfed by the parts of your program doing actual work, unless it’s in a very hot loop.

There used to be some much bigger perf issues with multimethods. Those were fixed long ago but the fud lingers.

Both are useful. If you are fundamentally doing type based dispatch, then use protocols. If not, use multimethods.

Thx

This is an old repo with some timings (needs an update) https://github.com/puredanger/poly-timing

updated those timings. kind of shocking how much better more recent jdk is on a few of those.

Hey all - perhaps a silly question here... I'm trying to use spec-tools and it seems like the conditional reader macro is being ignored when I import the CLJC file. Reference of the line: https://github.com/metosin/spec-tools/blob/master/src/spec_tools/impl.cljc#L3 Error:

user=> (require '[spec-tools.core])
Syntax error (FileNotFoundException) compiling at (spec_tools/impl.cljc:1:1).
Could not locate cljs/analyzer/api__init.class, cljs/analyzer/api.clj or cljs/analyzer/api.cljc on classpath.

Oops, wrong line: https://github.com/metosin/spec-tools/blob/master/src/spec_tools/impl.cljc#L5

I'm invoking it from Java, using tools.deps (updated add-libs branch as of 3 days ago) - am I missing something obvious here?

That probably won’t work with add-libs

Even if I'm not dynamically loading it? ie. a new clojure process?

Sorry, I misread above, thought you said reader literals

I assume you loaded it as a maven artifact?

add-libs will try to add a lib and it’s transitive deps in a way that meshes with the current full deps you have

are you sure the version of spec-tools you are using matches the code you are looking at on master?

Depending what those are, it may have used an older version of a dep that is incompatible with spec-tools

https://github.com/metosin/spec-tools/commit/b6054583244ff2448a0996402beab0ade0f260b2#diff-5540e5760a51fbb8e46e11f2195a4327 looks like the reader conditionals were added in 0.1.1

Can you try adding it to your deps and restarting your repl to remove the add-lib variable?

And what do you mean by “loading it from Java”?

Hey! Sorry all. Of course I get a call just as I ask...

So, clojure -Stree reports spec-tools as 0.10.0 - so I think we are good there.

Hi all. I’m getting ready to make the case for Clojure for a new work project (to a team who still use select! in ruby). One thing I’m concerned about is the additional deployment and maintenance overhead, particularly since I’ve not provisioned a server to run the JVM before (I come from a LAMP background). What’s the state of the art in deploying clojure apps right now? Are there standard, well-maintained docker images you can point an nginx instance at? And has anybody here worked with applications spread across JVM and non-JVM tech?

Loading it from java, I just mean that it's a Java process (so I expect cljs reader conditional to be ignored)

@jamie962 I don't think you need to worry too much. you can deploy clj apps to heroku if you expect scale, or if you are just running internally, all you need is a JRE installed

Got it working! Ended up deleting .cpcache... Not sure why that fixed it, but 🤷

personally for deploying clj apps internally, i'd use a docker image with java installed and just build and copy the jar file in

in fact,

https://hub.docker.com/_/clojure

@chrisjswanson thanks - good to know. we deploy to a kubernetes cluster anyway so the docker angle sounds like a good bet.

well the above may be your best friend then 🙂

so i can just copy an uberjar in to that container and then run it with java -jar?

yep

that’s easier than I expected

:thumbsup:

since you use k8s you have no worry of watching the process lifecycle, it's already handled

just java -jar and be free 🙂

super! thank you!

glad to help

if I did need to worry about process lifecycle, what sort of concerns would there be?

does the jvm quit after it hits memory limits?

(surely not)

well if you were just running in a vm , for example, then if your app crashed you'd need a nanny script to detect that and re-run it

oh right, yes

but that’s not a jvm/clj specific problem

but k8s will do it for you, just launch a new instance of the image

nope

java will crash if you go over your heap size

so if anticipate high memory usage,

I’m pretty au fait with most of this stuff, it’s where we sidle into jvm territory that I begin to lose confidence

https://stackoverflow.com/questions/3757223/jvm-options-using-leiningen

If you're using an uberjar to deploy, I suggest the adoptopenjdk images

If you need lein at runtime that's a different deal...

We use lein to build an uberjar, then run it in a standard Java container with java -jar

good point

clojure image maybe more intended for dev, and then just deploy with adoptopenjdk image. same pattern applies

you don't have to worry too much about JVM , I've found the metrics it exposes to actually be quite helpful. do look into key jvm metrics to track though, they can let you know if your app leaks memory, etc

Not coming from jvm world. What is the meaning for snapshot at the end of the release numbers? Can be removed?

E.g https://github.com/clj-commons/useful/blob/master/project.clj#L1

https://stackoverflow.com/questions/5901378/what-exactly-is-a-maven-snapshot-and-why-do-we-need-it#5901460

Is this applicable for clojure too?

it generally means "code that will eventually become the given version"

so 0.11.7-SNAPSHOT means, this is some code that exists somewhere between the release of 0.11.7 and the version before 0.11.7

OK so one should remember to remove it when realising 😁

...between 0.11.6 and...

so if you were cutting a release of some project you might switch from the snapshot version to the release version, cut the release, and then switch it to the next snapshot version

in general using snapshots is bad, it is using unreleased software

Another important thing to remember is that 0.11.7-SNAPSHOT can be a different artifact at different times so you don't want to depend on an artifact by name that could change out from under you.

a lot of projects don't publish snapshot artifacts anyway

For example, Clojure has daily builds and they are all named 1.11.0-master-SNAPSHOT every day -- and each of them could be different builds.

OK thx I got it

I might remove it

Since I don't plan to do so often releases.'😁

Currently I'm trying to do a o.o.1:grin:

Does this exception make sense to folks?

java.lang.ClassCastException: com.badlogic.gdx.physics.bullet.collision.SWIGTYPE_p_p_btCollisionObject cannot be cast to com.badlogic.gdx.physics.bullet.collision.btCollisionObject

So it seems im back to my original problem with clojurescript. I have a script I import into my nodejs project using a <script> tag in the public html file. now im trying to do unit testing and this workaround isnt working anymore. Any ideas of how to import a compiled clojurescript into a nodejs app?

you have a node.js server that is showing an HTML file with a ClojureScript app added via a script tag?

yeah

but now i cant even get my cljs file to build and im not sure what happened…

it doesnt give me a file name

java.lang.ClassCastException: clojure.lang.PersistentVector cannot be cast to clojure.lang.IPersistentMap at clojure.lang.RT.dissoc (RT.java:887) clojure.core$dissoc.invokeStatic (core.clj:1511) clojure.core$dissoc.invoke (core.clj:1504) leiningen.cljsbuild.config$backwards_compat_crossovers$fn__854.invoke (config.clj:70) clojure.core$map$fn__5851.invoke (core.clj:2753) clojure.lang.LazySeq.sval (LazySeq.java:42) clojure.lang.LazySeq.seq (LazySeq.java:51) clojure.lang.RT.seq (RT.java:531) clojure.lang.LazilyPersistentVector.create (LazilyPersistentVector.java:44) clojure.core$vec.invokeStatic (core.clj:377) clojure.core$vec.invoke (core.clj:367) leiningen.cljsbuild.config$backwards_compat_crossovers.invokeStatic (config.clj:70) leiningen.cljsbuild.config$backwards_compat_crossovers.invoke (config.clj:63) leiningen.cljsbuild.config$backwards_compat.invokeStatic (config.clj:77) leiningen.cljsbuild.config$backwards_compat.invoke (config.clj:76) leiningen.cljsbuild.config$normalize_options.invokeStatic (config.clj:152) leiningen.cljsbuild.config$normalize_options.invoke (config.clj:148) leiningen.cljsbuild.config$extract_options.invokeStatic (config.clj:185) leiningen.cljsbuild.config$extract_options.invoke (config.clj:179) leiningen.cljsbuild$cljsbuild.invokeStatic (cljsbuild.clj:258) leiningen.cljsbuild$cljsbuild.doInvoke (cljsbuild.clj:249) clojure.lang.RestFn.applyTo (RestFn.java:142) clojure.lang.Var.applyTo (Var.java:705) clojure.core$apply.invokeStatic (core.clj:667) clojure.core$apply.invoke (core.clj:660) leiningen.core.main$partial_task$fn__6592.doInvoke (main.clj:284) clojure.lang.RestFn.applyTo (RestFn.java:139) clojure.lang.AFunction$1.doInvoke (AFunction.java:31) clojure.lang.RestFn.applyTo (RestFn.java:137) clojure.core$apply.invokeStatic (core.clj:667) clojure.core$apply.invoke (core.clj:660) leiningen.core.main$apply_task.invokeStatic (main.clj:334) leiningen.core.main$apply_task.invoke (main.clj:320) leiningen.core.main$resolve_and_apply.invokeStatic (main.clj:343) leiningen.core.main$resolve_and_apply.invoke (main.clj:336) http://leiningen.do$do.invokeStatic (do.clj:40) http://leiningen.do$do.doInvoke (do.clj:32) clojure.lang.RestFn.applyTo (RestFn.java:139) clojure.lang.Var.applyTo (Var.java:705) clojure.core$apply.invokeStatic (core.clj:667) clojure.core$apply.invoke (core.clj:660) leiningen.core.main$partial_task$fn__6592.doInvoke (main.clj:284) clojure.lang.RestFn.applyTo (RestFn.java:139) clojure.lang.AFunction$1.doInvoke (AFunction.java:31) clojure.lang.RestFn.applyTo (RestFn.java:137) clojure.core$apply.invokeStatic (core.clj:667) clojure.core$apply.invoke (core.clj:660) leiningen.core.main$apply_task.invokeStatic (main.clj:334) leiningen.core.main$apply_task.invoke (main.clj:320) leiningen.core.main$resolve_and_apply.invokeStatic (main.clj:343) leiningen.core.main$resolve_and_apply.invoke (main.clj:336) leiningen.core.main$main$fn_6681.invoke (main.clj:452) leiningen.core.main$_main.invokeStatic (main.clj:442) leiningen.core.main$_main.doInvoke (main.clj:439) clojure.lang.RestFn.applyTo (RestFn.java:137) clojure.lang.Var.applyTo (Var.java:705) clojure.core$apply.invokeStatic (core.clj:665) clojure.main$main_opt.invokeStatic (main.clj:491) clojure.main$main_opt.invoke (main.clj:487) clojure.main$main.invokeStatic (main.clj:598) clojure.main$main.doInvoke (main.clj:561) clojure.lang.RestFn.applyTo (RestFn.java:137) clojure.lang.Var.applyTo (Var.java:705) clojure.main.main (main.java:37)

my guess would be an error in your project.clj

that would make sense for the error that was posted

as for unit tests, it doesn't sound like it has anything to do with node.js

once you've resolved the above error: how are you trying to run unit tests?

yeah that was most definitely the issue. thanks

the error above is independent from my nodejs problem. but i think i found what im looking for online, finally, but i wont know until i try it and see if it works. it is definitely something i havent tried yet so its worth a shot

i was trying what was described here and im having no luck so far https://lambdaisland.com/blog/2017-05-02-nodejs-scripts-clojurescript

@jason821 it sounds like you don't want to run your ClojureScript in Node.js though

you're including it as a script tag on an HTML page?

yeah

so is the ClojureScript supposed to run in the browser as a UI app, or is it supposed to run on the server side in Node.js?

which ever way it works tbh, but preferably in nodejs

because most of my project is written in javascript

that doesn't make sense to me

Node.js runs on the server, so you're not going be able to, for example, update the page dynamically based on your clojurescript code

what does your clojurescript code do?

i dont want to dynamically load it as clojurescript, nodejs will automatically refresh if anything changes

so if i have a compiled js file that works on nodejs, thats what i need

there are ways to compile CLJS to be imported into a Node.js runtime

I don't really know what you mean by "dynamically load it as clojurescript"

shadow-cljs is a build tool which has built-in configurations for developing node modules

that was your verbage lol

i compile the cljs manually, the nodejs will update it. ideally i would like to have cljs reload but thats not how my project is setup

im trying out shadow cljs and im trying to figure out if it will compile it to javascript to load in my nodejs app by importing it from javascript files

i could just be going about it the wrong way either way, the js file needs to import the clojurescript after its compiled to javascript

i have an idea, maybe im suppose to load the javascript app with shadow cljs instead of the other way around. but im not too sure since the app starting out being javascript