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  • Perfect hash in Scala.

    - by Lukasz Lew
    I have some class C: class C (...) { ... } I want to use it to index an efficient map. The most efficient map is an Array. So I add a "global" "static" counter in companion object to give each object unique id: object C { var id_counter = 0 } In primary constructor of C, with each creation of C I want to remember global counter value and increase it. Question 1: How to do it? Now I can use id in C objects as perfect hash to index array. But array does not preserve type information like map would, that a given array is indexed by C's id. Question 2: Is it possible to have it with type safety?

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  • Given two lines on a plane, how to find integer points closest to their interseciton?

    - by Lukasz Lew
    I can't solve it: You are given 8 integers: A, B, C representing a line on a plane with equation A*x + B*y = C a, b, c representing another line x, y representing a point on a plane The two lines are not parallel therefore divide plane into 4 pieces. Point (x, y) lies inside of one these pieces. Problem: Write a fast algorithm that will find a point with integer coordinates in the same piece as (x,y) that is closest to the cross point of the two given lines. Note: This is not a homework, this is old Euler-type task that I have absolutely no idea how to approach.

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  • Is it hard problem?

    - by Lukasz Lew
    I can't solve it: You are given 8 integers: A, B, C representing a line on a plane with equation A*x + B*y = C a, b, c representing another line x, y representing a point on a plane The two lines are not parallel therefore divide plane into 4 pieces. Point (x, y) lies inside of one these pieces. Problem: Write a fast algorithm that will find a point with integer coordinates in the same piece as (x,y) that is closest to the cross point of the two given lines. Note: This is not a homework, this is old Euler-type task that I have absolutely no idea how to approach.

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  • How can I run a package created with Simple Build Tool?

    - by Lukasz Lew
    I run: $ echo 'object Hi { def main(args: Array[String]) { println("Hi!") } }' > hw.scala $ sbt > warn Set log level to warn > run Hi! > package $ java -jar target/scala_2.7.7/test_2.7.7-1.0.jar Exception in thread "main" java.lang.NoClassDefFoundError: scala/ScalaObject at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:621) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124) at java.net.URLClassLoader.defineClass(URLClassLoader.java:260) Why can't I run this jar package this way?

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  • Is there a writable iterator in Java?

    - by Lukasz Lew
    In C+ one can use iterators for writing to a sequence. Simplest example would be: vector<int> v; for (vector<int>::iterator it = v.begin(); it!=v.end(); ++it) { *it = 42; } I need something more complicated - keep iterator as a class member for a later use. But I don't know how to get this behavior from Java iterators. Are there writable iterators in Java at all? If not then what replaces them?

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  • How do you create a Google Maps-esque drop down dialog?

    - by Daniel Lew
    In the Google Maps application, when you open the menu and click on "Directions", it pops up a dialog that is unique to Google Maps. It keeps the MapView in the background, but displays the search dialog from the top (or bottom, if you're on an old version of Android). I was curious if anyone knew how they achieved this effect. I'm willing to create a custom Dialog, but it seems that Dialogs are designed to pop into the middle of the screen (any other types of dialogs are denied permission as system dialogs). What trick is Google Maps using?

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  • Git: Stage into Commit, what is the right workflow?

    - by Lukasz Lew
    I just created a big piece of code I want to commit in several separate commits. So I can stage relevant parts, commit, stage, commit, ... and so on until I have all my changes commited. The missing part is how can I test whether I split the commit correcty. I.e. whether the part that is in staging area at least compiles? To do that I must somehow bring my work tree to be in sync with index (staging area) without losing the changes to be committed later. What is the right way to do it? What is the quickest way to do it? Update: How to do it with magit?

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  • Naming case classes in Scala.

    - by Lukasz Lew
    I tend to have this redundant naming in case classes: abstract class MyTree case class MyTreeNode (...) case class MyTreeLeaf (...) Isn't it possible to define Node and Leaf inside of MyTree? What are best practices here?

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  • Given two lines on a plane, how to find integer points closest to their intersection?

    - by Lukasz Lew
    I can't solve it: You are given 8 integers: A, B, C representing a line on a plane with equation A*x + B*y = C a, b, c representing another line x, y representing a point on a plane The two lines are not parallel therefore divide plane into 4 pieces. Point (x, y) lies inside of one these pieces. Problem: Write a fast algorithm that will find a point with integer coordinates in the same piece as (x,y) that is closest to the cross point of the two given lines. Note: This is not a homework, this is old Euler-type task that I have absolutely no idea how to approach. Update: You can assume that the 8 numbers on input are 32-bit signed integers. But you cannot assume that the solution will be 32 bit.

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  • Extending existing data structure in Scala.

    - by Lukasz Lew
    I have a normal tree defined in Scala. sealed abstract class Tree case class Node (...) extends Tree case class Leaf (...) extends Tree Now I want to add a member variable to all nodes and leaves in the tree. Is it possible with extend keyword or do I have to modify the tree classes by adding [T]?

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  • VS2008 project with Entity Framework model results in "always dirty" compile

    - by Jeremy Lew
    In VS 2008, I have a simple .csproj that contains an Entity Framework .edmx (V1) file. Every time I build the project, the output DLL is updated, even though nothing has changed. I have reproduced this in the simplest-possible project (containing one ordinary .cs file and one edmx model). If I remove the edmx model and build repeatedly, the output assembly will not be touched. If I add the edmx model and build repeatedly, the output assembly is modified each time. This is a problem because the real project is a dependency of dozens of other projects and it is wreaking havoc with what times when working in higher layers of the application. Is this a known problem? Any way to fix it? Thanks!

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  • Where is comprehensive documentation on Android's XML shapes?

    - by Daniel Lew
    I've been looking around for this for a long time but can never seem to find it in the Android documentation. There's all sorts of advanced things I see, but I can never find any solid documentation - there's the shapes package, but it provides no insight on how to use them in xml. The best I can do so far is finding other people's examples. Is there some magical documentation that exists for the XML shapes?

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  • How to minimize the amount of place used by GPL copyright notice?

    - by Lukasz Lew
    Gnu GPL page advocates a following header in each file of GPL project: This file is part of Foobar. Foobar is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Foobar is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Foobar. If not, see http://www.gnu.org/licenses/. I find this an over kill. Can't it be shorter and somehow refer to COPYING or LICENCE file?

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  • Qt layout problem.

    - by Lukasz Lew
    I have a following Qt code: QVBoxLayout* box = new QVBoxLayout; label = new QLabel(); // will be set later dynamically box->addWidget (label); Text in label will be set later. The problem is that when label resizes, it resizes QVBoxLayout, and it resizes other neighboring widgets. I don't want to make a label or layout fixed width. Because I want them to resize with a whole window. Is it possible to tell a widget to take all the place that it has in a layout, but not more?

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  • Is there a design pattern to cut down on code duplication when subclassing Activities in Android?

    - by Daniel Lew
    I've got a common task that I do with some Activities - downloading data then displaying it. I've got the downloading part down pat; it is, of course, a little tricky due to the possibility of the user changing the orientation or cancelling the Activity before the download is complete, but the code is there. There is enough code handling these cases such that I don't want to have to copy/paste it to each Activity I have, so I thought to create an abstract subclass Activity itself such that it handles a single background download which then launches a method which fills the page with data. This all works. The issue is that, due to single inheritance, I am forced to recreate the exact same class for any other type of Activity - for example, I use Activity, ListActivity and MapActivity. To use the same technique for all three requires three duplicate classes, except each extends a different Activity. Is there a design pattern that can cut down on the code duplication? As it stands, I have saved much duplication already, but it pains me to see the exact same code in three classes just so that they each subclass a different type of Activity.

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  • Have you actually convinced anybody to Scala?

    - by Lukasz Lew
    I had limited success myself. I was able to hype a few persons about Scala. But in fact none of them made a meaningful effort to try to switch (usually from Java). I would like to read both success and failure stories here. Both long tries and short ones. My goal is to find ways of presenting Scala to another person, friend, co-worker (not an audience) that will make them want to use this great language.

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