Anyone around at the moment who knows the details of how clojars versioning works? I've got a lib up that's at a stable production version, say 1.0.0. I'd like to put a snapshot of 2.0.0 up so that folks can kick the tires, but I don't want it to get displayed as the current version. Does anyone happen to recall what gets shown as the default if the newer version ends in -SNAPSHOT?

(I don't want to let it get shown as the default version, because I don't want folks to start using it when it may not be fully ready -- but I'd like to give beta testers easy access)

Not really answering your question @eggsyntax but if you use the new clj tool, you can use git deps. Point to a commit sha directly, no need to "release"

@eggsyntax if it ends in -SNAPSHOT anyone who switches to it deserves whatever they get

Ghadi can your lib be extended to make a jar not just an uberjar? Or are there better tools for that

Was looking at modifying it but it produced invalid jars with my changes. It looks like it relies on the dependencies manifest files?

Dunno, hadn't considered it. Right now we exclude all jar manifests

What kind of invalid jars?

Oh I thought you concated them

What is the simplest way to convert an int-array (INT_ARGB data from an image) to a byte-array ?

Not sure. I don't know jvm that well so I don't know what should be in there. Just modified it so I could specify the class path from command line rather than asking for the full class path

@qqq do you want one byte per int, or bytes representing the same bytes that would represent the ints?

@noisesmith: well, each int is 4 bytes packed into it, representing ARGB

so I want each int pulled apart into four bytes

ByteBuffer

you can push ints into a ByteBuffer, then read bytes out

in C, given memory layout, I can just cast the int* to an byte*

does JVM safety prevent me from doing such hacks ?

right, that's what ByteBuffer does for you

I don't know of a method to cast the pointers, but with ByteBuffer writes and reads you can get the same result

I don't get it, are you telling me to call putInt on ebery element of the int-array ? https://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer.html

that's exactly what I'm saying

then ask for the byte-array that's in it when you are done

It's the (doseq [i ...] (.putInt byteBufferObj i)) part that looks inefficient.

if you find a way to do it in java via a cast, let me know, I'd be fascinated

as far as I know there's no such thing

@qqq alternately you could just bit-mask and bit-shift the ints

ah i meant the META/INF stuff

(re-find #"^META-INF/services/" filename)
    :concat-lines

@noisesmith: an unrelated issue that is baffling me, PNG appears to be stored 0 - 255, java only has signed bytes, so "averaging" has interesting results.

@dpsutton that's only for java ServiceLoader / SPI business

most other META-INF stuff is ignored

@qqq there's a simple trick to get an unsigned value from the byte... let's see who finds it first

from what I have read, jvm does not ahveunsigned byte

so if you convert it, there would have to be some intermediate type

user=> (bit-and -1 0xFF) => 255

that's it

bit-and returns an int

type says Long, but sure, int

right, right

the original java trick uses & which returns an int 😄

oh ok. i need to look into what needs to be in a jar

so my XY problem is to start with a bufferedImage and read out a float[]

there is: https://docs.oracle.com/javase/7/docs/api/java/awt/image/Raster.html#getPixels(int,%20int,%20int,%20int,%20float[]) but the problem is, it apperas to be single channel

i'm porting chas emerick's URL lib into the new stuff. the current version is 5 years without a commit and in cljx land

wanted to use clj and coming up on needing artifacts

@dpsutton https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html

thanks so much

@dpsutton if there already is a maven artifact, you can just pull it with deps.edn

yeah, loads right up. but yes it would be nice to get rid of the cljx stuff

i mean create an artifact. one of the dependencies of URL is just as old. pathetic. i've got it converted and need to figure out how to make an artifact. but for sure you're right the rewrite could depend on a commit of it

For anyone who's curious about the question I brought up earlier re clojars: deploying a newer snapshot version to clojars does not make it the "default" version, ie the one shown on the main part of the page. It only appears in the sidebar. I'll paste a screenshot as a self-comment. @noisesmith @ghadi

https://docs.oracle.com/javase/8/docs/api/java/lang/String.html endsWith will do string -> string -> boolean is there a function which does string -> string (returning the actual suffix/extension/ part after the last .)

alright, I guess I can use:

(last (clojure.string/split "blah.txt" #"\."))

It's a simple regex, if you just want to get the extension

In Clojure+JVM, how do I do 'back pressure' ? I have one queue who's behaviour is: (java.util.concurrent.Executors/newFixedThreadPool 48) which basically says: create a queue where there are 48 workers popping stuff off now, when I submit things to this queue, I want to say: if there's < 1000 items, submit to this queue if there is >=1000 items, pause current thread until < 1000 items, then resubmit

is there a way in clojure to do keys-destructuring on something like:

(my-fn :arg-a "val-a" :arg-b "val-b" "non-map-value")

So, would this diagram (based on https://es.slideshare.net/adorepump/clojure-an-introduction-for-java-programmers ) be correct? (tried to add tagged literals)

I don’t think there are any lines between the data reader and the evaluator/compiler

And I don’t know what “program” is there at all

Where you have tagged elements those are also data structures

Hi, I was experimenting with a macro similar in concept to this one: (defmacro defdyn [name & body] '(def ^:dynamic ~name ~@body)) and I noticed that defining dynamic vars like this doesn’t seem to work, am I doing something wrong?

@inbox you are applying the metadata to the wrong symbol, try ~(vary-meta name assoc :dynamic true) instead of ^:dynamic ~name

yoo-hoo! thanks, that did it 🙂

now that you told me I see what was wrong, thanks!

1. Does the JVM use SSE instructions? 2. If so, if there anyway to control it? (I don't see it in the JVM bytecode).

look up -XX:+UseSuperWord option

I need a function where: input: namespace, symbol name output: string, which can be a valid Java classname I also need the function to be deterministic and one-to-one Suggestions ?

The Clojure compiler has a munge function to do this but it’s n to 1

As things like - and _ both map to _

1-1 is not that important; munge is good enough; thanks!

there’s a demunge too

(let [my-queue (java.util.concurrent.ArrayBlockingQueue. 5)
      my-pool (java.util.concurrent.ThreadPoolExecutor.
               24 24 0
               java.util.concurrent.TimeUnit/MILLISECONDS
               my-queue)]
  (doseq [i (range 10)]
    (println "before put queue " i)
    (.put my-queue
          (fn []
            (println "line " i)))
    (println "after put queue " i)))

How is the thread pool executor involved? I see it created but not used.

Nvm. I see it now.

that's not how ThreadPoolExecutor is supposed to be used

don't feed the queue directly, use ExecutorService methods

so the issue is that, if I use thre threadpool executor's .execute, if the queue is full, it rhwos an exception

however, if the queue is full, I want it to block

why do you need a ThreadPoolExecutor ? start N threads, make them poll the queue, then feed the queue

I don't have a good reason for using ThreadPoolExecutor. I saw that it was available, it seemed to proviide the right abstractions (managing tthe threadcpool for me), so I tried it. It's entirely possible the right solution is to manage threads manually. Is that what you suggest ?

@qqq it sounds like you want Executors/newFixedThreadPool

java.util.concurrent.Executors to be specific

@bfabry: when the "queue" hits a certai nsize, I want all enqueues to block -- newFixedThreadPool only provides: 1. unlimited queue or 2. throw exception on full

oh sorry you want to block the caller. yeah I don't think anything provides that out of the box

there's nothing wrong using threads directly if you know in advance what they're dedicated for

that's not normal thread pool behaviour

Let me ask another question. Do thread pools provide any mechanism for back pressure ?

kind of the same question isn't it? not unless you consider an exception back pressure

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ThreadPoolExecutor.html

core.async has a mechanism for back pressure. otherwise if your producer is only one thread it's easy enough to do yourself

section Queueing and RejectedTasks is what you want

@ghadi: yes, I'm aware of the possibility of throwing exception on queue being full; is there a way to turn this into a blocking op? the best I can do is turn this into a delay + retry

"It is possible to define and use other kinds of RejectedExecutionHandler classes"

using an unbounded queue and blocking is a bad idea. delay+retry sounds great to me

@qqq what about using CallerRunsPolicy? that is effectively blocking

and it's a form of backpressure surely

That's an interesting suggestion.

One way to write a ByteArrayOutputSream to a file is:

(let [baos (java.io.ByteArrayOutputStream.)
      os (java.io.FileOutputStream. out-fname)] 
  (.writeTo baos os))

hello everyone. I’m trying to generate a namespaced keyword from a string. "hello" -> ::hello is it possible to do this?

(keyword "hello") ;; => :hello
(keyword ":" "hello") ;; => ::/hello

@bravilogy ::hello is a shorthand for auto-namespacing to the current ns - one way to do it programatically would be (keyword (name (.name *ns*)) "hello")

(keyword (str *ns*) "foo") will product :currentNs/foo; or you can manually specify the ns with: (keyword "user" "foo")

oh I forgot (str *ns*) worked

Hi, when is expected to have Java 8 interop?

we already have java 8 interop?

can you explain what you're trying to do, your build tool settings, and any error messages you might be seeing?

I mean, functional interfaces

hmm, *ns* is not reliable, as in it doesn’t do what you’d expect

nothing stops you from interacting with functional interfaces

I wouldn't expect clojure core to ever have a syntax for them like java does of course

@jimenezsaezjoseantoni more specifically you can use reify or proxy to make an instance of Function or Producer etc.

but i think it would be helpful ifn interface match functional interfaces

so, there is no need to convert from one type of function to other

that's a separate question, even if we targetting minimum java 8 I'm not sure IFn would ever implement those interfacs

you don't need to convert - use reify or proxy instead of fn

out of curiousity, does https://github.com/ajoberstar/ike.cljj#converting-clojure-functions-to-java-sams do what you want?

also known as, I've never attempted to make use of Java's function stuff even within java, let alone Clojure

@noisesmith @tanzoniteblack thanks, that works! 🙂

It would be helpful for instance

(-> (Stream/of 1) (.map #(+ % 1)))

that does not work without making a reify

when writing jvm bytecode, is there a way to say: I highly recommend you inline this :invokestatic ?

no

you can give hints to the jvm at startup tho

actually it might be possible with some jvms through annotations

but likely to be internal details

but it doesn’t sound like a good idea anyway

Hi all, do you know of an alternative of with-redefs that is thread-safe so I can use it in a concurrent test-suite scenario?

@anler the two best ways to avoid with-redefs are to take stateful or out of scope elements as an argument so they can easily be substituted in a test (eg. stuartsierra/component simplifies doing this) or using a dynamic var so that it can have a per-thread binding

yes, I’m aware, ironically we are using component in the project I’m working on, but the business logic code is all coupled and I want to unit test a function with lots of deps to other functions

so I was using with-redefs but in my mind I had the idea it was binding, so it was a bit of a surprise when I saw my test suite failing 😛

I generally just dynamic variables in this case, @inbox.

but if what I want to mock is another function, those function vars aren’t dynamic right?

they can be

(defn ^:dynamic my-fn ...) works just fine

hmm, that might be a solution 🙂 thanks!

@anler I actually use component to decouple function logic (since I'm already paying for it to manage stateful things), and it makes testing much simpler

just pass in a hash map with stubs of the things you need, customized for testing

yeah, but our codebase needs a lot of changes before we are able to do that, I would do it but moving things around make my team nervous ¯\(ツ)/¯

you can also do this via a wrapper (not using component)

refactor the function to be tested to use a new function that takes an implementation as an argument

then instead of testing the function, test the implementation, passing in a stub

for example, one of the dependencies for our functions is a db, but that db is passed directly to jdbc functions, so I guess we should first create a DB protocol or something that decouples our code from jdbc itself, but doing such changes right now seems unlikely

you can just do this with a higher order function, no protocol needed

found this though, it seems it works, it might be the quick and dirty solution: https://gist.github.com/gfredericks/7143494

can you post an example?

from

(defn foo [db x] (blah db (bar x)))

(defn foo-impl [instance x] (instance (bar x))
 (defn foo [db x] (foo-impl (partial blah db) x))

@anler yeah, that gist does a few things that I'd be wary of. It's pretty much a hack

@anler the idea with the above is that you don't need to test (partial blah db) - it's some database function provided by your adaptor

so you can test foo-impl with a different stub replacign the db stuff

oh I see, I’ll take note and see how I can introduce such changes without too much drama 😄 thanks!

that pattern shouldn’t require more than splitting one function and making the second function a thin wrapper - definitely add a doc string describing why foo-impl exists though, because in my experience people will ask

and really the above could be a protocol with reify implementing it, but that tends to raise even more confusion

where a first class function makes it more “humble” and doesn’t make people assume some bigger design that isn’t there

yeah, I like it, to put you in context the function I’m trying to test is 57 lines long and depends on ~13 other functions 🙈

haha, that's an argument for refactor in itself

Can I use with-redefs to redefine a form within a let that's within a function?

usually about this point i refactor so that the thing i'm trying to reder is an argument

ok, so sounds like no 🙂

And is with-redefs not meant to be used in production?

I see the docstring...

>quote These temporary changes will be visible in all threads. Useful for mocking out functions during testing.

But wanted to double check

oh this isn't testing. that's a code smell to me. pretty big 🙂

this is testing actually

but I can see uses in production

aside from a code smell, any reason not to?

with-redef redefs named vars, which are by definition global, so by using it you immediately have global mutable state

even using it in tests is not great

I say that not as a dogmatic thing, but as someone who has worked on a large clojure code base with a large test suite that used with-redefs a lot, it sucks

if you are using with-redefs, whatever it is should be passed as an argument instead of def'ed as a global value

https://en.wikipedia.org/wiki/Java_bytecode_instruction_listings <-- are there no builtins for log / exp ?

I have a macro where I need the arguments to be evaluated first. I tried making it a function instead, but then the code I return doesn't get evaluated. So my only solutions right now are either to call eval on the args inside the macro, or call eval inside the function.

can you not do:

(defmacro foo
  [x y & body]
  `(let [x# ~x
         y# ~y]
     ; do stuff with body
     ,,,)

Except my arguments are inside & body

then you’ll need to parse the structure - this is one of the use-cases that clojure.spec was built for, so you could write a spec for the body and then use conform to pull out the pieces you need

you may want to rethink the design of this though if that turns out to be too complex; to me that points to a macro that is going to be hard to understand

Its the challenge of trying to wrap a spec macro inside another

can you write a sample "input to amcro" and "output to macro" pair so we can see what you have in mind?

Ya

combine-keys being the macro

and/or the function, since I need a and b in normal evaluation order, I don't really need a macro, but then I need to wrap combine-keys in an eval if I make it a function

Anyone have experience writing Cucumber tests in , then generating a class to be called in Java? Not sure if cucumber-jvm-clojure would help w/ that; it seems intended for writing Cucumber tests in and testing via a plugin. https://github.com/cucumber/cucumber-jvm-clojure

@didibus for that specifically, why not use s/merge?

I'm looking at: https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html https://docs.oracle.com/javase/8/docs/api/java/lang/Float.html and I see an exp(double) but no exp(float) Does exp only operate on doubles, and not floats ?

@greg316 Well, that's where things are a bit more complicated, I use a modified keys macro which prevents additonal keys, so it doesn't work with merge properly

Also, the return of describe which I use is different for a merge spec

Overall, I find its a situation I often get into. I want to control when the arguments would be evaluated, and maybe also when the return would be evaluated. What's the edge cases to watch out for when using eval or resolve in a macro?

resolve leads to spooky runtime errors with little clue at how to solve it, eval leads to bad performance

So, appart from performance and safety if used with untrusted input, eval executes in the same environment?

Would (defn foo [] (+ 10 global-symbol)) be equal to (defn bar [] (eval '(+ 10 global-symbol)))

you'd have to try and see, I forget some of the details of eval's environment resolution (I know it does not capture locals)

I guess my issue is I've always found it difficult to be sure of the context of eval, so I always worry there will be a scenario it fails

My macro is

(defn combine-keys [& kv] (eval `(su/keys ~@(mapcat identity (apply merge-with into kv)))))