I'm using the current version of the TypeSafe Scala/eclipse IDE. I have an object (which I called PositionObj to give it a unique name). PositionObj contains a main method. Yet when I try Run as > Scala application I get a pop-up message saying:
PositionObj needs to be an 'object' (it is currently a 'class').
In fact it's not a class, and there is no class with that name. Any thoughts about why this is happening and how I can get around it?
Here is the relevant code.
object PositionObj { ...
def main(args: Array[String] = Array[String]()): Unit = {
// This is just to see if anything happens.
println(position(3).p1Rqmts.keys.head)
}
...
Thanks.
Based on your answered-to code, try removing the default argument, since this might be creating a different code signature
I should have done this before, but now I notice that there is a compiler error message that says that the compiler couldn't handle the code because it was too big for a method. That's consistent with my experience with the problem. When I comment out a large table of data, everything works fine. So I'm now convinced that the problem was simply that the program was organized in a way that pieces of it were too large to be handled by the compiler.
I got around the problem by chopping my data table into multiple parts and including each one in a separate object. That worked even though all the objects were then included in the overall program. It was not the size of the program overall; it was the size of large chunks.
The compiler error message was somewhat misleading in that it said the problem was that a method was too large. In fact, my data table was a val in an object and not within a method. But as I said, chopping it up into separate objects and combing them with software solved the problem.
Related
I'm currently inserting an object into Drools working memory and running rules on it (creating a new object rather than updating the old one since I'm using Scala immutables...). From what I've understood, typically you would say something like update(myobject) and that would update the original variable inserted, letting you use the updated myObject in the main scope once the rules have been fired.
Since the objects I'm using (and inserting to memory) are immutable I can't simply modify them, and I'm having to create copies of them with slight tweaks.
Is there a way to return an object created within a rule's RHS? Perhaps by calling its FactHandle? Also open to other workarounds...
Alternatively, can I create a new object (newObject) and assign it the original's (myObject) FactHandle? Would that give me the access I need?
(Once again, I'm looking for a workaround to get Scala and Drools to work together.)
As far as I understand you problem, you could create a copy of the object with the tweaks you need and then you retract the old object and insert the new one. Something similar to:
val newObject = myObject.copy(foo = "bar");
retract(myObject);
insert(newObject);
I hope, it helps
After looking around and some prolonged trial and error I realised that FactHandles didn't quite work the way I expected. I was under the impression that they were an ID assigned to an object and that updating the object would mean that it kept its FactHandle (apparently not).
I went about this by creating a new (Scala) object and running update in the RHS of the rule as follows:
update(kcontext.getKieRuntime().getFactHandle(myObject), newObject)
While this worked fine within the rule-firing process, it was tedious to retrieve the object from the Main app afterwards. Calling ksession.getFactHandle(myObject) on the original object returned null after the rules had been fired and, as it turns out, the FactHandle of this object had indeed changed when checked by printing it out from within a rule.
The workaround for this was to save the original object's FactHandle before firing the rules (i.e. val objectFH = ksession.insert(myObject)) and to call .getObject using that FactHandle after the rules were fired (even though the FactHandle saved in this variable had changed).
In all honesty, I'm still unsure about why this works since the FactHandle changes on update, however I'm pretty sure this stems from my lack of understanding on how FactHandles work. If anyone would care to elaborate in the comments I'd be more than happy to add it in the answer for future reference.
(Thanks to #laune for helping point me back to my previous questions)
I have my own emulation of java.util.Timer (and quite a lot of other stuff missing in GWT). I have even a JUnit test proving it works in the browser.
I've just tried to convert some third-party library to GWT, which needed a Timer, and in some part of it, I call:
SystemUtils.getTimer().scheduleAtFixedRate(timerTask, value, value);
But the GWT compiler turns getTimer().scheduleAtFixedRate() to:
getTimer().nullMethod()
SystemUtils.getTimer() is a static method. I have googled for nullMethod(), but most hits are about:
null.nullMethod();
That doesn't apply to me. What could be going wrong, and what can I do to fix it?
[EDIT] Actually, the java.util.Timer emulation itself works, but it seems that (atm?) SystemUtils.getTimer() returns "undefined". Could that be the reason? Since getTimer() returns an instance created dynamically, how could the GWT compiler possibly make any assumption about the return value of getTimer(), and the presence/usage of the methods of the Timer type?
When I have seen this kind of errors it was caused by unreachable code: GWT had determined that some code was not reachable, turning off compilation for some stuff, but then it still somehow tried to link the unreachable code, showing this kind of errors.
For completeness sake
If this error shows up (which often happens after deploying to App Engine) then compile without obfuscation, turn off super dev mode, restart jetty and refresh the browser. Open the generated javascript and find where the problem occurs by searching for 'nullMethod'. You'll see that the compiler may have removed whole chunks of code that it believes is 'unreachable'.
The code surrounding 'null.nullMethod' is probably very different than what you expected. The simplest way around this is to add a null /undefined check and initializing whatever variable that is generated as 'null'. This forces the compiler to reconsider because now the variable can never be null and the code that follows it must be reachable.
For example, if null.nullMethod is found and 'null' is actually supposed to be var a = ... then add if(a == null) { a = ""; } before it (in Java of course).
For anybody who struggles with this null.nullMethod issue:
It may be possible that your GWT compiler isn't able to find the properties of your JSON bean object if your object variable is declared with its interface type:
MyTypeIF item = ...;
...
item.getStart();
...
In my scenario, GWT compiled that into:
MyTypeIF item = ...;
...
null.nullMethod();
...
Instead, I had to declare and cast it to its real implementation class:
JSMyType item = (JSMyType)...;
...
I created an app that works which is similar to the examples from the Marmalade SDK. Then I tried to move the IwUIController derived class in a separate files .h/.cpp to clean the code up a bit but I get a crash every time I try to access any IwUIElement? For example:
CIwUIImage* image = IwSafeCast<CIwUIImage*>(pScreen->GetChildNamed("Image"));
pScreen is declared as
static CIwUIElement *pScreen;
and then in main(): pScreen = CIwUIElement::CreateFromResource("Screen");
What can be the reason for these crashes? Does the Controller class need to be in the same file as main()? I've tried to debug and the pointer appears to be passed properly.
Not sure it really counts as an answer, but I don't have enough stackoverflow reputation to comment apparently;-)
If you've got C++ code that worked OK until you split it into two files, I would seriously check the #include and other declarations are the same in the new two files as they were in the originals. 9 times out of 10, my experience is that for some reason something is not the same. Actually one specific issue worth checking for is that a struct or class is only partly declared (e.g. a forward declaration) in one file and has lost its parent.
Having said that, as Creator, said what were the symptoms of the crash? Is this possibly the dynamic cast failing of IwSafeCast failing?
I tried searching on google, and got literally no results when trying to figure out what this means. My console is logging:
objc[17048]: Class _NSZombie_GEOLatLng is implemented in both ?? and ??. One of the two will be used. Which one is undefined.
objc[17048]: Class _NSZombie_GEOLatLng is implemented in both ?? and ??. One of the two will be used. Which one is undefined.
objc[17048]: Class _NSZombie_GEOLocation is implemented in both ?? and ??. One of the two will be used. Which one is undefined.
objc[17048]: Class _NSZombie_GEOLocation is implemented in both ?? and ??. One of the two will be used. Which one is undefined.
Anyone seen this before, or have any idea what it means, what's causing it, and if it's a problem?
I've seen it. Specifically, on OS X - but the cause should be the same. GEOLocation (and others) is defined in two images which are loaded into the process.
If that were a class you wrote, the class' symbols are defined in multiple object files (would likely be a linker error though…), in the linked libraries, loaded bundles, or some combination of - when code may be loaded dynamically.
If it's not a class you wrote (or synthesized), file a bug with the creator of the class.
It's also possible that the class is defined in your app, and also defined in a linked library. In that event, you would need to change the name of your class.
It is definitely a problem. The class (with that name) is being loaded into the objc runtime twice, and there are no guarantees as to which implementation will be returned when an instance is created since objc uses a flat namespace.
In this case, the class exists in the system frameworks so... send it to the bug reporter - it deserves be fixed quickly.
This is a harmless warning that occurs when you have enabled zombie warnings in the build scheme. You can ignore it.
I had this obscure message and noticed that a NIB had been removed from the project, but code was still using it. You may want to check if any resources have been removed from the bundle that are still in use.
...and why has the package this misleading name (I assumed it had something to do with JavaME or mobile/smart phones)?
I found no references on the internet about scala.mobile.Code or scala.mobile.Location at all nor did I manage to do anything with those classes except getting ClassCastExcetions or NoSuchMethodErrors.
Actually there is not even a single test against scala.mobile in the Scala's test tree which could help understanding that code.
The classes really smell like they were forgotten in the source tree a long time ago and got accidentally released since that.
Maybe I just missed something about them?
Update:
scala.mobile was removed in Scala 2.9.
I just checked the source code.
When Scala changed the name mangling of class files a few years ago and it seems people forgot to update these classes accordingly.
So my answer would be:
At least Location has no purpose, because it is not possible to get anything sensible out of it (except exceptions) and Code without Location is severely limited. It works though if you pass the class literal to Code directly:
import scala.mobile._
val c = new Code(classOf[scala.collection.mutable.StringBuilder])
c.apply[StringBuilder, String]("append")("Foo")
c.apply[String]("toString")() // returns "Foo"
c.apply[Int]("length")() // returns 3
Looks like yet-another implementation in the standard library of reflection-slightly-nicer.
The description of Location pretty much explains what that is about:
The class Location provides a create method to instantiate objects
from a network location by specifying the URL address of the jar/class file.
It might be used by remote actors. Maybe.
As for why it has this misleading name? Well, back in 2004 smart phones had really low penetration, so maybe the association wasn't all that strong.