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  • Why is my Scala function returning type Unit and not whatever is the last line?

    - by Andy
    I am trying to figure out the issue, and tried different styles that I have read on Scala, but none of them work. My code is: .... val str = "(and x y)"; def stringParse ( exp: String, pos: Int, expreshHolder: ArrayBuffer[String], follow: Int ) var b = pos; //position of where in the expression String I am currently in val temp = expreshHolder; //holder of expressions without parens var arrayCounter = follow; //just counts to make sure an empty spot in the array is there to put in the strings if(exp(b) == '(') { b = b + 1; while(exp(b) == ' '){b = b + 1} //point of this is to just skip any spaces between paren and start of expression type if(exp(b) == 'a') { temp(arrayCounter) = exp(b).toString; b = b+1; temp(arrayCounter)+exp(b).toString; b = b+1; temp(arrayCounter) + exp(b).toString; arrayCounter+=1} temp; } } val hold: ArrayBuffer[String] = stringParse(str, 0, new ArrayBuffer[String], 0); for(test <- hold) println(test); My error is: Driver.scala:35: error: type mismatch; found : Unit required: scala.collection.mutable.ArrayBuffer[String] ho = stringParse(str, 0, ho, 0); ^one error found When I add an equals sign after the arguments in the method declaration, like so: def stringParse ( exp: String, pos: Int, expreshHolder: ArrayBuffer[String], follow: Int ) ={....} It changes it to "Any". I am confused on how this works. Any ideas? Much appreciated.

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  • Why is Scala's type inferencer not able to resolve this?

    - by Levi Greenspan
    In the code snippet below - why do I have to give a type annotation for Nil? Welcome to Scala version 2.8.0.RC2 (OpenJDK Server VM, Java 1.6.0_18). Type in expressions to have them evaluated. Type :help for more information. scala> List(Some(1), Some(2), Some(3), None).foldLeft(Nil)((lst, o) => o match { case Some(i) => i::lst; case None => lst }) <console>:6: error: type mismatch; found : List[Int] required: object Nil List(Some(1), Some(2), Some(3), None).foldLeft(Nil)((lst, o) => o match { case Some(i) => i::lst; case None => lst }) ^ scala> List(Some(1), Some(2), Some(3), None).foldLeft(Nil:List[Int])((lst, o) => o match { case Some(i) => i::lst; case None => lst }) res1: List[Int] = List(3, 2, 1)

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  • Type classes or implicit parameters? What do you prefer and why? [closed]

    - by Petr Pudlák
    I was playing a bit with Scalaz and I realized that Haskell's type classes are very similar to Scala's implicit parameters. While Haskell passes the methods defined by a type class using hidden dictionaries, Scala allows a similar thing using implicit parameters. For example, in Haskell, one could write: incInside :: (Functor f) => f Int -> f Int incInside = fmap (+ 1) and the same function using Scalaz: import scalaz._; import Scalaz._; def incInside[F[_]](x: F[Int])(implicit fn: Functor[F]): F[Int] = fn.fmap(x, (_:Int) + 1); I wonder: If you could choose (i.e. your favorite language would offer both), what would you pick - implicits or type classes? And what are your pros/cons?

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  • Book (or resource) on Java bytecode

    - by Andrea
    I am looking for some resources on the JVM bytecode. Ideally I would for a short book; something more than a blog post but not a 800 pages tome. If it is relevant, I am a Scala developer, not a Java one, although I know Java just fine. I would like something that allowed me to read JVM bytecode and answer questions such as: Why does the bytecode has to know about high level construct such as classes? Are subtyping relations still visible in bytecode? How does type erasure work exactly? How do Oracle and Dalvik bytecode differ, and what consequences does this have for, say, developing Android apps with Scala? How does the JVM manage the stack, and why exactly this creates issues with tail call elimination? and so on.

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  • Constraints while designing the Java generics

    - by Andrea
    Java generics look quite different from those available in Scala, although both were designed by Martin Odersky. From my point of view, the design of generics in Java is worse, for instance: there is no possibility to specify variance one can get around the previous limitation by using wildcards, but this means the burden of specifying variance goes on the caller instead of the library designer one cannot use a type constructor in generics What were the constraints in Java that forced Odersky to design this mechanism for generics instead of the more flexible one he devised for Scala? Was he just savvier a few years later or there were actual limitations due to Java?

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  • Oracle ZS3 Contest for Partners: Share an unforgettable experience at the Teatro Alla Scala in Milan

    - by Claudia Caramelli-Oracle
    12.00 Dear valued Partner, We are pleased to launch a partner contest exclusive to our partners dedicated to promoting and selling Oracle Systems! You are essential to the success of Oracle and we want to recognize your contribution and effort in driving Oracle Storage to the market. To show our appreciation we are delighted to announce a contest, giving the winners the opportunity to attend a roundtable chaired by Senior Oracle Executives and spend an unforgettable evening at the magnificent Teatro Alla Scala in Milan, followed by a stay at the Grand Hotel et de Milan, courtesy of Oracle. Recognition will be given to 12 partner companies (10 VARs & 2 VADs) who will be recognized for their ZFS storage booking achievement in the broad market between June 1st and July 18th 2014. Criteria of Eligibility A minimum deal value of $30k is required for qualification Partners who are wholly or partially owned by a public sector organization are not eligible for participation  Winners The winning VARs will be: The highest ZS3 or ZBA bookings achievers by COB on July 18th, 2014 in each Oracle EMEA region (1) The highest Oracle on Oracle (2) ZS3 or ZBA bookings achievers by COB on July 18th, 2014 in each Oracle EMEA region The winning VADs (3) will be: The highest ZS3 or ZBA bookings achiever by COB on July 18th 2014 in EMEA The highest Oracle on Oracle (2) ZS3 or ZBA bookings achiever by COB on July 18th 2014 in EMEA  The Prize Winners will be invited to participate to a roundtable chaired by Oracle on Monday September 8th 2014 in Milan and to be guests of Oracle in the evening of September 8th, 2014 at the Teatro Alla Scala. The evening will comprise of a private tour of the Scala museum, cocktail reception at the elegant museum rooms and attending the performance by the renowned Soprano, Maria Agresta. Our guests will then retire for the evening to the Grand Hotel et de Milan, courtesy of Oracle. Oracle shall be the final arbiter in selecting the winners and all winners will be notified via their Oracle account manager.Full details about the contest, expenses covered by Oracle and timetable of events can be found on the Oracle EMEA Hardware (Servers & Storage) Partner Community workspace (FY15 Q1 ZFS Partner Contest). Remember: access to the community workspace requires membership. If you are not a member please register here. Good Luck!! For more information, please contact Sasan Moaveni. (1) Two VAR winners for each EMEA region – Eastern Europe & CIS, Middle East & Africa, South Europe, North Europe, UK/Ireland & Israel - as per the criteria outlined above (2) Oracle on Oracle, in this instance, means ZS3 or ZBA storage attached to DB or DB options, Engineered Systems or Sparc servers sold to the same customer by the same partner within the contest timelines.(3) Two VAD winners, one for each of the criteria outlined above, will be selected from across EMEA. Normal 0 14 false false false IT X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;}

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  • Does C# have an equivalent to Scala's structural typing?

    - by Tom Morris
    In Scala, I can define structural types as follows: type Pressable { def press(): Unit } This means that I can define a function or method which takes as an argument something that is Pressable, like this: def foo(i: Pressable) { // etc. The object which I pass to this function must have defined for it a method called press() that matches the type signature defined in the type - takes no arguments, returns Unit (Scala's version of void). I can even use the structural type inline: def foo(i: { def press(): Unit }) { // etc. It basically allows the programmer to have all the benefits of duck typing while still having the benefit of compile-time type checking. Does C# have something similar? I've Googled but can't find anything, but I'm not familiar with C# in any depth. If there aren't, are there any plans to add this?

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  • Scala: Can I nudge a combinator parser to be locally greedy?

    - by eed3si9n
    Suppose I have an ambiguous language expressed in combinator parser. Is there a way to make certain expressions locally greedy? Here's an example of what I mean. import scala.util.parsing.combinator._ object Example extends JavaTokenParsers { def obj: Parser[Any] = (shortchain | longchain) ~ anyrep def longchain: Parser[Any] = zero~zero~one~one def shortchain: Parser[Any] = zero~zero def anyrep: Parser[Any] = rep(any) def any: Parser[Any] = zero | one def zero: Parser[Any] = "0" def one: Parser[Any] = "1" def main(args: Array[String]) { println(parseAll(obj, args(0) )) } } After compiling, I can run it as follows: $ scala Example 001111 [1.7] parsed: ((0~0)~List(1, 1, 1, 1)) I would like to somehow instruct the first part of obj to be locally greedy and match with longchain. If I switch the order around, it matches the longchain, but that's not because of the greediness. def obj: Parser[Any] = (longchain | shortchain) ~ anyrep

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  • When is a scala partial function not a partial function?

    - by Fred Haslam
    While creating a map of String to partial functions I ran into unexpected behavior. When I create a partial function as a map element it works fine. When I allocate to a val it invokes instead. Trying to invoke the check generates an error. Is this expected? Am I doing something dumb? Comment out the check() to see the invocation. I am using scala 2.7.7 def PartialFunctionProblem() = { def dream()() = { println("~Dream~"); new Exception().printStackTrace() } val map = scala.collection.mutable.HashMap[String,()=>Unit]() map("dream") = dream() // partial function map("dream")() // invokes as expected val check = dream() // unexpected invocation check() // error: check of type Unit does not take parameters }

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  • Scala and HttpClient: How do I resolve this error?

    - by Benjamin Metz
    I'm using scala with Apache HttpClient, and working through examples. I'm getting the following error: /Users/benjaminmetz/IdeaProjects/JakartaCapOne/src/JakExamp.scala Error:Error:line (16)error: overloaded method value execute with alternatives (org.apache.http.HttpHost,org.apache.http.HttpRequest)org.apache.http.HttpResponse <and> (org.apache.http.client.methods.HttpUriRequest,org.apache.http.protocol.HttpContext)org.apache.http.HttpResponse cannot be applied to (org.apache.http.client.methods.HttpGet,org.apache.http.client.ResponseHandler[String]) val responseBody = httpclient.execute(httpget, responseHandler) Here is the code with the error and line in question highlighted: import org.apache.http.client.ResponseHandler import org.apache.http.client.HttpClient import org.apache.http.client.methods.HttpGet import org.apache.http.impl.client.BasicResponseHandler import org.apache.http.impl.client.DefaultHttpClient object JakExamp { def main(args : Array[String]) : Unit = { val httpclient: HttpClient = new DefaultHttpClient val httpget: HttpGet = new HttpGet("www.google.com") println("executing request..." + httpget.getURI) val responseHandler: ResponseHandler[String] = new BasicResponseHandler val responseBody = httpclient.execute(httpget, responseHandler) // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ println(responseBody) client.getConnectionManager.shutdown } } I can successfully run the example in java...

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  • Can I create a collection in Scala that uses different equals/hashCode/compare implementations?

    - by Willis Blackburn
    I'm looking for as simple way to create an identity set. I just want to be able to keep track of whether or not I've "seen" a particular object while traversing a graph. I can't use a regular Set because Set uses "==" (the equals method in Scala) to compare elements. What I want is a Set that uses "eq." Is there any way to create a Set in Scala that uses some application-specified method for testing equality rather than calling equals on the set elements? I looked for some kind of "wrapEquals" method that I could override but did not find it. I know that I could use Java's IdentityHashMap, but I'm looking for something more general-purpose. Another idea I had was to just wrap each set element in another object that implements equals in terms of eq, but it's wasteful to generate tons of new objects just to get a new equals implementation. Thanks!

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  • Can i have a negative value as constant expression in Scala?

    - by Klinke
    I have an Java-Annotation that return a double value: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface DoubleValue { double value(); } When i try to attach the annotation to a field in a scala class and the value is negativ like here: class Test { @DoubleValue(-0.05) var a = _ } i get an compiler error with the message: "annotation argument needs to be a constant; found: 0.05.unary_-". I understood that i need a numerical literal and i looked into the Scala Language Specification and it seems, that the - sign is only used for the exponent but not for the mantissa. Does someone has an idea how i can have a negative value as runtime information using annotations? Thanks, Klinke

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  • How to make a Scala Applet whose Applet class is a singleton?

    - by Jamie
    Hi, I don't know if a solution exists but it would be highly desirable. I'm making a Scala Applet, and I want the main Applet class to be a singleton so it can be accessed elsewhere in the applet, sort of like: object App extends Applet { def init { // do init here } } Instead I have to make the App class a normal instantiatable class otherwise it complains because the contructor is private. So the ugly hack I have is to go: object A { var pp: App = null } class App extends Applet { A.pp = this def init { // do init here } } I really hate this, and is one of the reasons I don't like making applets in Scala right now. Any better solution? It would be nice...

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  • Overloading on return type ???

    - by Green Hyena
    scala> val shares = Map("Apple" -> 23, "MicroSoft" -> 50, "IBM" -> 17) shares: scala.collection.immutable.Map[java.lang.String,Int] = Map(Apple -> 23, MicroSoft -> 50, IBM -> 17) scala> val shareholders = shares map {_._1} shareholders: scala.collection.immutable.Iterable[java.lang.String] = List(Apple, MicroSoft, IBM) scala> val newShares = shares map {case(k, v) => (k, 1.5 * v)} newShares: scala.collection.immutable.Map[java.lang.String,Double] = Map(Apple -> 34.5, MicroSoft -> 75.0, IBM -> 25.5) From this example it seems like the map method is overloaded on return type. Overloading on return type is not possible right? Would somebody please explain what's going on here?

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  • Why does the Scala compiler disallow overloaded methods with default arguments?

    - by soc
    While there might be valid cases where such method overloadings could become ambiguous, why does the compiler disallow code which is neither ambiguous at compile time nor at run time? Example: // This fails: def foo(a: String)(b: Int = 42) = a + b def foo(a: Int) (b: Int = 42) = a + b // This fails, too. Even if there is no position in the argument list, // where the types are the same. def foo(a: Int) (b: Int = 42) = a + b def foo(a: String)(b: String = "Foo") = a + b // This is OK: def foo(a: String)(b: Int) = a + b def foo(a: Int) (b: Int = 42) = a + b // Even this is OK. def foo(a: Int)(b: Int) = a + b def foo(a: Int)(b: String = "Foo") = a + b val bar = foo(42)_ // This complains obviously ... Are there any reasons why these restrictions can't be loosened a bit? Especially when converting heavily overloaded Java code to Scala default arguments are a very important and it isn't nice to find out after replacing plenty of Java methods by one Scala methods that the spec/compiler imposes arbitrary restrictions.

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  • Is it possible in Scala to force the caller to specify a type parameter for a polymorphic method ?

    - by Alex Kravets
    //API class Node class Person extends Node object Finder { def find[T <: Node](name: String): T = doFind(name).asInstanceOf[T] } //Call site (correct) val person = find[Person]("joe") //Call site (dies with a ClassCast inside b/c inferred type is Nothing) val person = find("joe") In the code above the client site "forgot" to specify the type parameter, as the API writer I want that to mean "just return Node". Is there any way to define a generic method (not a class) to achieve this (or equivalent). Note: using a manifest inside the implementation to do the cast if (manifest != scala.reflect.Manifest.Nothing) won't compile ... I have a nagging feeling that some Scala Wizard knows how to use Predef.<:< for this :-) Ideas ?

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  • Poll: What is stopping you from switching (from Java) to Scala ?

    - by Lukasz Lew
    What would make you to switch to Scala ? If you are negative on the switching to Scala, please state the reason as well (or upvote). As with all StackOverflow Poll type Q&As, please make certain your answer is NOT listed already before adding a new answer If it already exists, vote that one up so we see what the most popular answer is, rather than duplicating an existing entry. If you see a duplicate, vote it down. If you have interesting or additional information to add, use a comment or edit the original entry rather than creating a duplicate.

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  • Modern Java alternatives

    - by Ralph
    I'm not sure if stackoverflow is the best forum for this discussion. I have been a Java developer for 14 years and have written an enterprise-level (~500,000 line) Swing application that uses most of the standard library APIs. Recently, I have become disappointed with the progress that the language has made to "modernize" itself, and am looking for an alternative for ongoing development. I have considered moving to the .NET platform, but I have issues with using something the only runs well in Windows (I know about Mono, but that is still far behind Microsoft). I also plan on buying a new Macbook Pro as soon as Apple releases their new rumored Arrandale-based machines and want to develop in an environment that will feel "at home" in Unix/Linux. I have considered using Python or Ruby, but the standard Java library is arguably the largest of any modern language. In JVM-based languages, I looked at Groovy, but am disappointed with its performance. Rumor has it that with the soon-to-be released JDK7, with its InvokeDynamic instruction, this will improve, but I don't know how much. Groovy is also not truly a functional language, although it provides closures and some of the "functional" features on collections. It does not embrace immutability. I have narrowed my search down to two JVM-based alternatives: Scala and Clojure. Each has its strengths and weaknesses. I am looking for the stackoverflow readerships' opinions. I am not an expert at either of these languages; I have read 2 1/2 books on Scala and am currently reading Stu Halloway's book on Clojure. Scala is strongly statically typed. I know the dynamic language folks claim that static typing is a crutch for not doing unit testing, but it does provide a mechanism for compile-time location of a whole class of errors. Scala is more concise than Java, but not as much as Clojure. Scala's inter-operation with Java seems to be better than Clojure's, in that most Java operations are easier to do in Scala than in Clojure. For example, I can find no way in Clojure to create a non-static initialization block in a class derived from a Java superclass. For example, I like the Apache commons CLI library for command line argument parsing. In Java and Scala, I can create a new Options object and add Option items to it in an initialization block as follows (Java code): final Options options = new Options() { { addOption(new Option("?", "help", false, "Show this usage information"); // other options } }; I can't figure out how to the same thing in Clojure (except by using (doit...)), although that may reflect my lack of knowledge of the language. Clojure's collections are optimized for immutability. They rarely require copy-on-write semantics. I don't know if Scala's immutable collections are implemented using similar algorithms, but Rich Hickey (Clojure's inventor) goes out of his way to explain how that language's data structures are efficient. Clojure was designed from the beginning for concurrency (as was Scala) and with modern multi-core processors, concurrency takes on more importance, but I occasionally need to write simple non-concurrent utilities, and Scala code probably runs a little faster for these applications since it discourages, but does not prohibit, "simple" mutability. One could argue that one-off utilities do not have to be super-fast, but sometimes they do tasks that take hours or days to complete. I know that there is no right answer to this "question", but I thought I would open it up for discussion. If anyone has a suggestion for another JVM-based language that can be used for enterprise level development, please list it. Also, it is not my intent to start a flame war. Thanks, Ralph

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  • Modern alternatives to Java

    - by Ralph
    I have been a Java developer for 14 years and have written an enterprise-level (~500 kloc) Swing application that uses most of the standard library APIs. Recently, I have become disappointed with the progress that the language has made to "modernize" itself, and am looking for an alternative for ongoing development. I have considered moving to the .NET platform, but I have issues with using something the only runs well in Windows (I know about Mono, but that is still far behind Microsoft). I also plan on buying a new Macbook Pro as soon as Apple releases their new rumored Arrandale-based machines and want to develop in an environment that will feel "at home" in Unix/Linux. I have considered using Python or Ruby, but the standard Java library is arguably the largest of any modern language. In JVM-based languages, I looked at Groovy, but am disappointed with its performance. Rumor has it that with the soon-to-be released JDK7, with its InvokeDynamic instruction, this will improve, but I don't know how much. Groovy is also not truly a functional language, although it provides closures and some of the "functional" features on collections. It does not embrace immutability. I have narrowed my search down to two JVM-based alternatives: Scala and Clojure. Each has its strengths and weaknesses. I am looking for opinions. I am not an expert at either of these languages; I have read 2 1/2 books on Scala and am currently reading Stu Halloway's book on Clojure. Scala is strongly statically typed. I know the dynamic language folks claim that static typing is a crutch for not doing unit testing, but it does provide a mechanism for compile-time location of a whole class of errors. Scala is more concise than Java, but not as much as Clojure. Scala's inter-operation with Java seems to be better than Clojure's, in that most Java operations are easier to do in Scala than in Clojure. For example, I can find no way in Clojure to create a non-static initialization block in a class derived from a Java superclass. For example, I like the Apache commons CLI library for command line argument parsing. In Java and Scala, I can create a new Options object and add Option items to it in an initialization block as follows (Java code): final Options options = new Options() { { addOption(new Option("?", "help", false, "Show this usage information"); // other options } }; I can't figure out how to the same thing in Clojure (except by using (doit...)), although that may reflect my lack of knowledge of the language. Clojure's collections are optimized for immutability. They rarely require copy-on-write semantics. I don't know if Scala's immutable collections are implemented using similar algorithms, but Rich Hickey (Clojure's inventor) goes out of his way to explain how that language's data structures are efficient. Clojure was designed from the beginning for concurrency (as was Scala) and with modern multi-core processors, concurrency takes on more importance, but I occasionally need to write simple non-concurrent utilities, and Scala code probably runs a little faster for these applications since it discourages, but does not prohibit, "simple" mutability. One could argue that one-off utilities do not have to be super-fast, but sometimes they do tasks that take hours or days to complete. I know that there is no right answer to this "question", but I thought I would open it up for discussion. Are there other JVM-based languages that can be used for enterprise level development?

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  • Functional Methods on Collections

    - by GlenPeterson
    I'm learning Scala and am a little bewildered by all the methods (higher-order functions) available on the collections. Which ones produce more results than the original collection, which ones produce less, and which are most appropriate for a given problem? Though I'm studying Scala, I think this would pertain to most modern functional languages (Clojure, Haskell) and also to Java 8 which introduces these methods on Java collections. Specifically, right now I'm wondering about map with filter vs. fold/reduce. I was delighted that using foldRight() can yield the same result as a map(...).filter(...) with only one traversal of the underlying collection. But a friend pointed out that foldRight() may force sequential processing while map() is friendlier to being processed by multiple processors in parallel. Maybe this is why mapReduce() is so popular? More generally, I'm still sometimes surprised when I chain several of these methods together to get back a List(List()) or to pass a List(List()) and get back just a List(). For instance, when would I use: collection.map(a => a.map(b => ...)) vs. collection.map(a => ...).map(b => ...) The for/yield command does nothing to help this confusion. Am I asking about the difference between a "fold" and "unfold" operation? Am I trying to jam too many questions into one? I think there may be an underlying concept that, if I understood it, might answer all these questions, or at least tie the answers together.

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  • 2011 Tech Goal Review

    - by kerry
    A year ago I wrote a post listing my professional goals for 2011.  I thought I would review them and see how I did. Release an Android app to the marketplace – Didn’t do it.  In fact, haven’t really touched Android much since I wrote that.  I still have some ideas but am not sure if I will get around to it. Contribute free software to the community – I did do this.  I have been collaborating with others via github more lately. Regularly attend a user group meetings outside of Java – Did not do this.  Family life being what it is makes this not that much of a priority right now. Obtain the Oracle Certified Web Developer Certification – Did not do this.  This is not much of a priority to me any more. Learn scala – I am about 50/50 on this one.  I read a few scala books but did not write an actual application. Write an app using JSF – Did not do this.  Still interested. Present at a user group meeting – I did a Maven presentation at the Java user group. Use git more, and more effectively – Definitely did this.  Using it on a daily basis now. Overall, I got about halfway on my goals.  It’s not too bad since I did do a few things that weren’t on my list. Learned to develop applications using GWT and deploy them to Google App Engine Converted one of my sites from PHP to Ruby / Sinatra (learning to use it in the process) Studied up on the HTML 5 features and did a lot of Javascript development

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  • Performance of concurrent software on multicore processors

    - by Giorgio
    Recently I have often read that, since the trend is to build processors with multiple cores, it will be increasingly important to have programming languages that support concurrent programming in order to better exploit the parallelism offered by these processors. In this respect, certain programming paradigms or models are considered well-suited for writing robust concurrent software: Functional programming languages, e.g. Haskell, Scala, etc. The actor model: Erlang, but also available for Scala / Java (Akka), C++ (Theron, Casablanca, ...), and other programming languages. My questions: What is the state of the art regarding the development of concurrent applications (e.g. using multi-threading) using the above languages / models? Is this area still being explored or are there well-established practices already? Will it be more complex to program applications with a higher level of concurrency, or is it just a matter of learning new paradigms and practices? How does the performance of highly concurrent software compare to the performance of more traditional software when executed on multiple core processors? For example, has anyone implemented a desktop application using C++ / Theron, or Java / Akka? Was there a boost in performance on a multiple core processor due to higher parallelism?

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  • Functional programming compared to OOP with classes

    - by luckysmack
    I have been interested in some of the concepts of functional programming lately. I have used OOP for some time now. I can see how I would build a fairly complex app in OOP. Each object would know how to do things that object does. Or anything it's parents class does as well. So I can simply tell Person().speak() to make the person talk. But how do I do similar things in functional programming? I see how functions are first class items. But that function only does one specific thing. Would I simply have a say() method floating around and call it with an equivalent of Person() argument so I know what kind of thing is saying something? So I can see the simple things, just how would I do the comparable of OOP and objects in functional programming, so I can modularize and organize my code base? For reference, my primary experience with OOP is Python, PHP, and some C#. The languages that I am looking at that have functional features are Scala and Haskell. Though I am leaning towards Scala. Basic Example (Python): Animal(object): def say(self, what): print(what) Dog(Animal): def say(self, what): super().say('dog barks: {0}'.format(what)) Cat(Animal): def say(self, what): super().say('cat meows: {0}'.format(what)) dog = Dog() cat = Cat() dog.say('ruff') cat.say('purr')

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