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  • php values of one array to key of another array

    - by mark
    I have 2 arrays $arr1 = Array ( [0] => 12 [1] => 4 [2] => 8 [3] => xx [4] => 1 [5] => 1year [6] => 7 ) $arr2 = Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 [6] => 7 ) I want to create a new array with the values of a2 as keys in $arr1. My resultant array should be like this $arr3 = Array ( [1] => 12 [2] => 4 [3] => 8 [4] => xx [5] => 1 [6] => 1year [7] => 7 )

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  • Selecting dictionary items by key efficiently in Python

    - by user248237
    suppose I have a dictionary whose keys are strings. How can I efficiently make a new dictionary from that which contains only the keys present in some list? for example: # a dictionary mapping strings to stuff mydict = {'quux': ..., 'bar': ..., 'foo': ...} # list of keys to be selected from mydict keys_to_select = ['foo', 'bar', ...] The way I came up with is: filtered_mydict = [mydict[k] for k in mydict.keys() \ if k in keys_to_select] but I think this is highly inefficient because: (1) it requires enumerating the keys with keys(), (2) it requires looking up k in keys_to_select each time. at least one of these can be avoided, I would think. any ideas? I can use scipy/numpy too if needed.

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  • Foreign Key Relationships

    - by Yehonathan Quartey
    I have two models class Subject(models.Model): name = models.CharField(max_length=100,choices=COURSE_CHOICES) created = models.DateTimeField('created', auto_now_add=True) modified = models.DateTimeField('modified', auto_now=True) syllabus = models.FileField(upload_to='syllabus') def __unicode__(self): return self.name and class Pastquestion(models.Model): subject=models.ForeignKey(Subject) year =models.PositiveIntegerField() questions = models.FileField(upload_to='pastquestions') def __unicode__(self): return str(self.year) Each Subject can have one or more past questions but a past question can have only one subject. I want to get a subject, and get its related past questions of a particular year. I was thinking of fetching a subject and getting its related past question. Currently am implementing my code such that I rather get the past question whose subject and year correspond to any specified subject like this_subject=Subject.objects.get(name=the_subject) thepastQ=Pastquestion.objects.get(year=2000,subject=this_subject) I was thinking there is a better way to do this. Or is this already a better way? Please Do tell ?

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  • limiting mysql results by range of a specific key INCLUDING DUPLICATES

    - by aVC
    I have a query SELECT p.*, m.*, (SELECT COUNT(*) FROM newPhotoonAlert n WHERE n.userIDfor='$id' AND n.threadID=p.threadID and n.seen='0') AS unReadCount FROM posts p JOIN myMembers m ON m.id = p.user_id LEFT JOIN following f ON (p.user_id = f.user_id AND f.follower_id='$id' AND f.request='0' AND f.status='1') JOIN myMembers searcher ON searcher.id = '$id' WHERE ((f.follower_id = searcher.id) OR m.id='$id') AND p.flagged <'5' ORDER BY p.threadID DESC,p.positionID It brings result as expected but I want to add Another CLAUSE to limit the results. Say a sample (minimal shown) set of data looks like this with the above query. threadID postID positionID url 564 1254 2 a.com 564 1245 1 a1.com 541 1215 3 b1.com 541 1212 2 b2.com 541 1210 1 b3.com 523 745 1 c1.com 435 689 2 d2.com 435 688 1 a4.com 256 345 1 s3.com 164 316 1 f1.com . . I want to get ROWS corresponding to 2 DISTINCT threadIDs starting from MAX, but I want to include duplicates as well. Something like AND p.threadID IN (Select just Two of all threadIDs currently selected, but include duplicate rows) So my result should be threadID postID positionID url 564 1254 2 a.com 564 1245 1 a1.com 541 1215 3 b1.com 541 1212 2 b2.com 541 1210 1 b3.com

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  • Foreign-key-like merge in R

    - by skyl
    I'm merging a bunch of csv with 1 row per id/pk/seqn. > full = merge(demo, lab13am, by="seqn", all=TRUE) > full = merge(full, cdq, by="seqn", all=TRUE) > full = merge(full, mcq, by="seqn", all=TRUE) > full = merge(full, cfq, by="seqn", all=TRUE) > full = merge(full, diq, by="seqn", all=TRUE) > print(length(full$ridageyr)) [1] 9965 > print(summary(full$ridageyr)) Min. 1st Qu. Median Mean 3rd Qu. Max. 0.00 11.00 19.00 29.73 48.00 85.00 Everything is great. But, I have another file which has multiple rows per id like: "seqn","rxd030","rxd240b","nhcode","rxq250" 56,2,"","",NA,NA,"" 57,1,"ACETAMINOPHEN","01200",2 57,1,"BUDESONIDE","08800",1 58,1,"99999","",NA 57 has two rows. So, if I naively try to merge this file, I have a ton more rows and my data gets all skewed up. > full = merge(full, rxq, by="seqn", all=TRUE) > print(length(full$ridageyr)) [1] 15643 > print(summary(full$ridageyr)) Min. 1st Qu. Median Mean 3rd Qu. Max. 0.00 14.00 41.00 40.28 66.00 85.00 Is there a normal idiomatic way to deal with data like this? Suppose I want a way to make a simple model like MYSPECIAL_FACTOR <- somehow() glm(MYSPECIAL_FACTOR ~ full$ridageyr, family=binomial) where MYSPECIAL_FACTOR is, say, whether or not rxd240b == "ACETAMINOPHEN" for the observations which are unique by seqn. You can reproduce by running the first bit of this.

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  • Ruby 1.9 regex as a hash key

    - by Liutauras
    I am trying this example myhash = {/(\d+)/ => "hello"} with ruby 1.9.2p136 (2010-12-25) [i386-mingw32]. It doesn't work as expected (edit: as it turned out it shouldn't work as I was expecting): irb(main):004:0> myhash = {/(\d+)/ => "hello"} => {/(\d+)/=>"Hello"} irb(main):005:0> myhash[2222] => nil irb(main):006:0> myhash["2222"] => nil In Rubular which is on ruby1.8.7 the regex works. What am I missing?

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  • php array_filter without key preservation

    - by pistacchio
    Hi, if i filter an array with array_filter to eliminate null values, keys are preserved and this generated "holes" in the array. Eg: The filtered version of [0] => 'foo' [1] => null [2] => 'bar' is [0] => 'foo' [2] => 'bar' How can i get, instead [0] => 'foo' [1] => 'bar' ? Thanks

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  • sort list(of string()) using a variable index into string() as key - vb.net

    - by tullynyguy
    I have a List(of String()). I have written a custom comparer (implements IComparer(of string)) to do an alphanumeric sort. Is there a way to sort the List using a given index to determine which position in the String() to sort by? In other words one time I might sort by Index = 0 and another time by Index = 3. The length of all String() in the list is the same. For reference this question is similar to Sort List<String[]> except I am using VB.net and that question is hardwired to Index=0.

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  • Multiple key presses doing different events in C#

    - by Nevik Eeirnb
    Hi, private void Form1_KeyDown(object sender, KeyEventArgs e) { if (e.KeyCode == Keys.W) player1.moveUp(); if (e.KeyCode == Keys.NumPad8) player2.moveUp(); } In the above code the moveUp methods basically just increment a value. I want it so both keys can be pressed (or held down)at the same time and both events will trigger. Thanks, Nevik

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  • Access php multidimensional array key based on a variable string

    - by ggirtsou
    I have stored the XML path to items in a string like this: response->items->item. What I need to do is to access an array called $xml_array like this: $xml_array['response']['items']['item'] When I write it in the code it works. The thing is that I want it to be done on the fly. I use this to convert response->items->item to ['response']['items']['item']: $xml_path = 'response->items->item'; $explode_path = explode('->', $xml_path); $correct_string = false; foreach($explode_path as $path) { $correct_string .= '[\''.$path.'\']'; } the problem is that I can't access $xml_array by doing this: $xml_array[$correct_string] So I end up with this: $xml_tag = 'title'; $xml_path = 'response->items->item'; $correct_string = '$items = $xml2array'; $explode_path = explode('->', $xml_path); foreach($explode_path as $path) { $correct_string .= '[\''.$path.'\']'; } $correct_string .= ';'; eval($correct_string); foreach($items as $item) { echo $item[$xml_tag].'<br />'; } and access the $xml_array array through $items array. Is there any way I can do this and avoid using eval()? Thanks in advance!

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  • Delete data with foreign key in SQL Server table

    - by Andha
    I'm going to delete data in an SQL Server table (parent) which has a relationship with another table (child). I tried the basic Delete query. But it isn't working (and I know it won't). DELETE FROM table WHERE ... It returned following error The DELETE statement conflicted with the REFERENCE constraint ... I need to keep the table's schema. I know that I just need to add some words in the query, I've ever done this before, but I just couldn't recall it.

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  • Custom Content Pipeline with Automatic Serialization Load Error

    - by Direweasel
    I'm running into this error: Error loading "desert". Cannot find type TiledLib.MapContent, TiledLib, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null. at Microsoft.Xna.Framework.Content.ContentTypeReaderManager.InstantiateTypeReader(String readerTypeName, ContentReader contentReader, ContentTypeReader& reader) at Microsoft.Xna.Framework.Content.ContentTypeReaderManager.GetTypeReader(String readerTypeName, ContentReader contentReader, List1& newTypeReaders) at Microsoft.Xna.Framework.Content.ContentTypeReaderManager.ReadTypeManifest(Int32 typeCount, ContentReader contentReader) at Microsoft.Xna.Framework.Content.ContentReader.ReadHeader() at Microsoft.Xna.Framework.Content.ContentReader.ReadAsset[T]() at Microsoft.Xna.Framework.Content.ContentManager.ReadAsset[T](String assetName, Action1 recordDisposableObject) at Microsoft.Xna.Framework.Content.ContentManager.Load[T](String assetName) at TiledTest.Game1.LoadContent() in C:\My Documents\Dropbox\Visual Studio Projects\TiledTest\TiledTest\TiledTest\Game1.cs:line 51 at Microsoft.Xna.Framework.Game.Initialize() at TiledTest.Game1.Initialize() in C:\My Documents\Dropbox\Visual Studio Projects\TiledTest\TiledTest\TiledTest\Game1.cs:line 39 at Microsoft.Xna.Framework.Game.RunGame(Boolean useBlockingRun) at Microsoft.Xna.Framework.Game.Run() at TiledTest.Program.Main(String[] args) in C:\My Documents\Dropbox\Visual Studio Projects\TiledTest\TiledTest\TiledTest\Program.cs:line 15 When trying to run the game. This is a basic demo to try and utilize a separate project library called TiledLib. I have four projects overall: TiledLib (C# Class Library) TiledTest (Windows Game) TiledTestContent (Content) TMX CP Ext (Content Pipeline Extension Library) TiledLib contains MapContent which is throwing the error, however I believe this may just be a generic error with a deeper root problem. EMX CP Ext contains one file: MapProcessor.cs using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Content.Pipeline; using Microsoft.Xna.Framework.Content.Pipeline.Graphics; using Microsoft.Xna.Framework.Content.Pipeline.Processors; using Microsoft.Xna.Framework.Content; using TiledLib; namespace TMX_CP_Ext { // Each tile has a texture, source rect, and sprite effects. [ContentSerializerRuntimeType("TiledTest.Tile, TiledTest")] public class DemoMapTileContent { public ExternalReference<Texture2DContent> Texture; public Rectangle SourceRectangle; public SpriteEffects SpriteEffects; } // For each layer, we store the size of the layer and the tiles. [ContentSerializerRuntimeType("TiledTest.Layer, TiledTest")] public class DemoMapLayerContent { public int Width; public int Height; public DemoMapTileContent[] Tiles; } // For the map itself, we just store the size, tile size, and a list of layers. [ContentSerializerRuntimeType("TiledTest.Map, TiledTest")] public class DemoMapContent { public int TileWidth; public int TileHeight; public List<DemoMapLayerContent> Layers = new List<DemoMapLayerContent>(); } [ContentProcessor(DisplayName = "TMX Processor - TiledLib")] public class MapProcessor : ContentProcessor<MapContent, DemoMapContent> { public override DemoMapContent Process(MapContent input, ContentProcessorContext context) { // build the textures TiledHelpers.BuildTileSetTextures(input, context); // generate source rectangles TiledHelpers.GenerateTileSourceRectangles(input); // now build our output, first by just copying over some data DemoMapContent output = new DemoMapContent { TileWidth = input.TileWidth, TileHeight = input.TileHeight }; // iterate all the layers of the input foreach (LayerContent layer in input.Layers) { // we only care about tile layers in our demo TileLayerContent tlc = layer as TileLayerContent; if (tlc != null) { // create the new layer DemoMapLayerContent outLayer = new DemoMapLayerContent { Width = tlc.Width, Height = tlc.Height, }; // we need to build up our tile list now outLayer.Tiles = new DemoMapTileContent[tlc.Data.Length]; for (int i = 0; i < tlc.Data.Length; i++) { // get the ID of the tile uint tileID = tlc.Data[i]; // use that to get the actual index as well as the SpriteEffects int tileIndex; SpriteEffects spriteEffects; TiledHelpers.DecodeTileID(tileID, out tileIndex, out spriteEffects); // figure out which tile set has this tile index in it and grab // the texture reference and source rectangle. ExternalReference<Texture2DContent> textureContent = null; Rectangle sourceRect = new Rectangle(); // iterate all the tile sets foreach (var tileSet in input.TileSets) { // if our tile index is in this set if (tileIndex - tileSet.FirstId < tileSet.Tiles.Count) { // store the texture content and source rectangle textureContent = tileSet.Texture; sourceRect = tileSet.Tiles[(int)(tileIndex - tileSet.FirstId)].Source; // and break out of the foreach loop break; } } // now insert the tile into our output outLayer.Tiles[i] = new DemoMapTileContent { Texture = textureContent, SourceRectangle = sourceRect, SpriteEffects = spriteEffects }; } // add the layer to our output output.Layers.Add(outLayer); } } // return the output object. because we have ContentSerializerRuntimeType attributes on our // objects, we don't need a ContentTypeWriter and can just use the automatic serialization. return output; } } } TiledLib contains a large amount of files including MapContent.cs using System; using System.Collections.Generic; using System.Globalization; using System.Xml; using Microsoft.Xna.Framework.Content.Pipeline; namespace TiledLib { public enum Orientation : byte { Orthogonal, Isometric, } public class MapContent { public string Filename; public string Directory; public string Version = string.Empty; public Orientation Orientation; public int Width; public int Height; public int TileWidth; public int TileHeight; public PropertyCollection Properties = new PropertyCollection(); public List<TileSetContent> TileSets = new List<TileSetContent>(); public List<LayerContent> Layers = new List<LayerContent>(); public MapContent(XmlDocument document, ContentImporterContext context) { XmlNode mapNode = document["map"]; Version = mapNode.Attributes["version"].Value; Orientation = (Orientation)Enum.Parse(typeof(Orientation), mapNode.Attributes["orientation"].Value, true); Width = int.Parse(mapNode.Attributes["width"].Value, CultureInfo.InvariantCulture); Height = int.Parse(mapNode.Attributes["height"].Value, CultureInfo.InvariantCulture); TileWidth = int.Parse(mapNode.Attributes["tilewidth"].Value, CultureInfo.InvariantCulture); TileHeight = int.Parse(mapNode.Attributes["tileheight"].Value, CultureInfo.InvariantCulture); XmlNode propertiesNode = document.SelectSingleNode("map/properties"); if (propertiesNode != null) { Properties = new PropertyCollection(propertiesNode, context); } foreach (XmlNode tileSet in document.SelectNodes("map/tileset")) { if (tileSet.Attributes["source"] != null) { TileSets.Add(new ExternalTileSetContent(tileSet, context)); } else { TileSets.Add(new TileSetContent(tileSet, context)); } } foreach (XmlNode layerNode in document.SelectNodes("map/layer|map/objectgroup")) { LayerContent layerContent; if (layerNode.Name == "layer") { layerContent = new TileLayerContent(layerNode, context); } else if (layerNode.Name == "objectgroup") { layerContent = new MapObjectLayerContent(layerNode, context); } else { throw new Exception("Unknown layer name: " + layerNode.Name); } // Layer names need to be unique for our lookup system, but Tiled // doesn't require unique names. string layerName = layerContent.Name; int duplicateCount = 2; // if a layer already has the same name... if (Layers.Find(l => l.Name == layerName) != null) { // figure out a layer name that does work do { layerName = string.Format("{0}{1}", layerContent.Name, duplicateCount); duplicateCount++; } while (Layers.Find(l => l.Name == layerName) != null); // log a warning for the user to see context.Logger.LogWarning(string.Empty, new ContentIdentity(), "Renaming layer \"{1}\" to \"{2}\" to make a unique name.", layerContent.Type, layerContent.Name, layerName); // save that name layerContent.Name = layerName; } Layers.Add(layerContent); } } } } I'm lost as to why this is failing. Thoughts? -- EDIT -- After playing with it a bit, I would think it has something to do with referencing the projects. I'm already referencing the TiledLib within my main windows project (TiledTest). However, this doesn't seem to make a difference. I can place the dll generated from the TiledLib project into the debug folder of TiledTest, and this causes it to generate a different error: Error loading "desert". Cannot find ContentTypeReader for Microsoft.Xna.Framework.Content.Pipeline.ExternalReference`1[Microsoft.Xna.Framework.Content.Pipeline.Graphics.Texture2DContent]. at Microsoft.Xna.Framework.Content.ContentTypeReaderManager.GetTypeReader(Type targetType, ContentReader contentReader) at Microsoft.Xna.Framework.Content.ContentTypeReaderManager.GetTypeReader(Type targetType) at Microsoft.Xna.Framework.Content.ReflectiveReaderMemberHelper..ctor(ContentTypeReaderManager manager, FieldInfo fieldInfo, PropertyInfo propertyInfo, Type memberType, Boolean canWrite) at Microsoft.Xna.Framework.Content.ReflectiveReaderMemberHelper.TryCreate(ContentTypeReaderManager manager, Type declaringType, FieldInfo fieldInfo) at Microsoft.Xna.Framework.Content.ReflectiveReader1.Initialize(ContentTypeReaderManager manager) at Microsoft.Xna.Framework.Content.ContentTypeReaderManager.ReadTypeManifest(Int32 typeCount, ContentReader contentReader) at Microsoft.Xna.Framework.Content.ContentReader.ReadHeader() at Microsoft.Xna.Framework.Content.ContentReader.ReadAsset[T]() at Microsoft.Xna.Framework.Content.ContentManager.ReadAsset[T](String assetName, Action1 recordDisposableObject) at Microsoft.Xna.Framework.Content.ContentManager.Load[T](String assetName) at TiledTest.Game1.LoadContent() in C:\My Documents\Dropbox\Visual Studio Projects\TiledTest\TiledTest\TiledTest\Game1.cs:line 51 at Microsoft.Xna.Framework.Game.Initialize() at TiledTest.Game1.Initialize() in C:\My Documents\Dropbox\Visual Studio Projects\TiledTest\TiledTest\TiledTest\Game1.cs:line 39 at Microsoft.Xna.Framework.Game.RunGame(Boolean useBlockingRun) at Microsoft.Xna.Framework.Game.Run() at TiledTest.Program.Main(String[] args) in C:\My Documents\Dropbox\Visual Studio Projects\TiledTest\TiledTest\TiledTest\Program.cs:line 15 This is all incredibly frustrating as the demo doesn't appear to have any special linking properties. The TiledLib I am utilizing is from Nick Gravelyn, and can be found here: https://bitbucket.org/nickgravelyn/tiledlib. The demo it comes with works fine, and yet in recreating I always run into this error.

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  • Why do my LWJGL fonts have dots and lines around them?

    - by Jordan
    When we render fonts there are weird dots and lines around the text. I have no idea why this would happen. Here is an image of what it looks like: Our font class looks like this: package me.NJ.ComputerTycoon.Font; import me.NJ.ComputerTycoon.BaseObjects.UDim2; import org.lwjgl.opengl.Display; import org.newdawn.slick.Color; import org.newdawn.slick.TrueTypeFont; public class Font { public TrueTypeFont font; private int fontSize = 18; private String fontName = "Calibri"; private int fontStyle = java.awt.Font.BOLD; public Font(String fontName, int fontStyle, int fontSize) { font = new TrueTypeFont(new java.awt.Font(fontName, fontStyle, fontSize), true); //font. } public Font(int fontStyle, int fontSize) { font = new TrueTypeFont(new java.awt.Font(fontName, fontStyle, fontSize), true); } public Font(int fontSize) { font = new TrueTypeFont(new java.awt.Font(fontName, fontStyle, fontSize), true); } public Font() { font = new TrueTypeFont(new java.awt.Font(fontName, fontStyle, fontSize), true); } public void drawString(int x, int y, String s, Color color){ this.font.drawString(x, y, s, color); } public void drawString(int x, int y, String s){ this.font.drawString(x, y, s); } public void drawString(float x, float y, String s, Color color){ this.font.drawString(x, y, s, color); } public void drawString(float x, float y, String s){ this.font.drawString(x, y, s); } public void drawString(UDim2 udim, String s){ this.font.drawString((Display.getWidth() * udim.getX().getScale()) + udim.getX().getOffset(), (Display.getHeight() * udim.getY().getScale()) + udim.getY().getOffset(), s); } public String getFontName(){ return this.fontName; } public int getFontSize(){ return this.fontSize; } public TrueTypeFont getFont(){ return this.font; } } What could be causing this?

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  • This code is of chess game. What is represented by 'DISTANCE' in code? [closed]

    - by rajeshverma423
    package chess; public class Evaluate { public static final int PIECE_KING = 0; public static final int PIECE_QUEEN = 1; public static final int PIECE_ROOK = 2; public static final int PIECE_BISHOP = 3; public static final int PIECE_KNIGHT = 4; public static final int PIECE_PAWN = 5; public static final int FULL_BIT_RANK = 4080; public static final int LAZY_MARGIN = 100; public static final int ISOLATED_PENALTY = 10; public static final int DOUBLE_PENALTY = 4; public static final int[] PIECE_VALUE = { 0, 9, 5, 3, 3, 1 }; public static final int[] PASS_PAWN = { 0, 35, 30, 20, 10, 5 }; public static final byte[] DISTANCE = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 5, 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 5, 4, 3, 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 7, 6, 5, 4, 3, 2, 3, 4, 5, 6, 7, 0, 0, 0, 0, 7, 6, 5, 4, 3, 2, 1, 2, 3, 4, 5, 6, 7, 0, 0, 7, 6, 5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 5, 6, 7, 0, 0, 7, 6, 5, 4, 3, 2, 1, 2, 3, 4, 5, 6, 7, 0, 0, 0, 0, 7, 6, 5, 4, 3, 2, 3, 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 7, 6, 5, 4, 3, 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 5, 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7 };

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  • Box2D how to implement a camera?

    - by Romeo
    By now i have this Camera class. package GameObjects; import main.Main; import org.jbox2d.common.Vec2; public class Camera { public int x; public int y; public int sx; public int sy; public static final float PIXEL_TO_METER = 50f; private float yFlip = -1.0f; public Camera() { x = 0; y = 0; sx = x + Main.APPWIDTH; sy = y + Main.APPHEIGHT; } public Camera(int x, int y) { this.x = x; this.y = y; sx = x + Main.APPWIDTH; sy = y + Main.APPHEIGHT; } public void update() { sx = x + Main.APPWIDTH; sy = y + Main.APPHEIGHT; } public void moveCam(int mx, int my) { if(mx >= 0 && mx <= 80) { this.x -= 2; } else if(mx <= Main.APPWIDTH && mx >= Main.APPWIDTH - 80) { this.x += 2; } if(my >= 0 && my <= 80) { this.y += 2; } else if(my <= Main.APPHEIGHT && my >= Main.APPHEIGHT - 80) { this.y -= 2; } this.update(); } public float meterToPixel(float meter) { return meter * PIXEL_TO_METER; } public float pixelToMeter(float pixel) { return pixel / PIXEL_TO_METER; } public Vec2 screenToWorld(Vec2 screenV) { return new Vec2(screenV.x + this.x, yFlip * screenV.y + this.y); } public Vec2 worldToScreen(Vec2 worldV) { return new Vec2(worldV.x - this.x, yFlip * worldV.y - this.y); } } I need to know how to modify the screenToWorld and worldToScreen functions to include the PIXEL_TO_METER scaling.

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  • Confused about implementing Single Responsibility Principle

    - by HichemSeeSharp
    Please bear with me if the question looks not well structured. To put you in the context of my issue: I am building an application that invoices vehicles stay duration in a parking. In addition to the stay service there are some other services. Each service has its own calculation logic. Here is an illustration (please correct me if the design is wrong): public abstract class Service { public int Id { get; set; } public bool IsActivated { get; set; } public string Name { get; set } public decimal Price { get; set; } } public class VehicleService : Service { //MTM : many to many public virtual ICollection<MTMVehicleService> Vehicles { get; set; } } public class StayService : VehicleService { } public class Vehicle { public int Id { get; set; } public string ChassisNumber { get; set; } public DateTime? EntryDate { get; set; } public DateTime? DeliveryDate { get; set; } //... public virtual ICollection<MTMVehicleService> Services{ get; set; } } Now, I am focusing on the stay service as an example: I would like to know at invoicing time which class(es) would be responsible for generating the invoice item for the service and for each vehicle? This should calculate the duration cost knowing that the duration could be invoiced partially so the like is as follows: not yet invoiced stay days * stay price per day. At this moment I have InvoiceItemsGenerator do everything but I am aware that there is a better design.

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  • Is there a name for the Builder Pattern where the Builder is implemented via interfaces so certain parameters are required?

    - by Zipper
    So we implemented the builder pattern for most of our domain to help in understandability of what actually being passed to a constructor, and for the normal advantages that a builder gives. The one twist was that we exposed the builder through interfaces so we could chain required functions and unrequired functions to make sure that the correct parameters were passed. I was curious if there was an existing pattern like this. Example below: public class Foo { private int someThing; private int someThing2; private DateTime someThing3; private Foo(Builder builder) { this.someThing = builder.someThing; this.someThing2 = builder.someThing2; this.someThing3 = builder.someThing3; } public static RequiredSomething getBuilder() { return new Builder(); } public interface RequiredSomething { public RequiredDateTime withSomething (int value); } public interface RequiredDateTime { public OptionalParamters withDateTime (DateTime value); } public interface OptionalParamters { public OptionalParamters withSeomthing2 (int value); public Foo Build ();} public static class Builder implements RequiredSomething, RequiredDateTime, OptionalParamters { private int someThing; private int someThing2; private DateTime someThing3; public RequiredDateTime withSomething (int value) {someThing = value; return this;} public OptionalParamters withDateTime (int value) {someThing = value; return this;} public OptionalParamters withSeomthing2 (int value) {someThing = value; return this;} public Foo build(){return new Foo(this);} } } Example of how it's called: Foo foo = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).build(); Foo foo2 = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).withSomething2(3).build();

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  • Which order to define getters and setters in? [closed]

    - by N.N.
    Is there a best practice for the order to define getters and setters in? There seems to be two practices: getter/setter pairs first getters, then setters (or the other way around) To illuminate the difference here is a Java example of getter/setter pairs: public class Foo { private int var1, var2, var3; public int getVar1() { return var1; } public void setVar1(int var1) { this.var1 = var1; } public int getVar2() { return var2; } public void setVar2(int var2) { this.var2 = var2; } public int getVar3() { return var3; } public void setVar3(int var3) { this.var3 = var3; } } And here is a Java example of first getters, then setters: public class Foo { private int var1, var2, var3; public int getVar1() { return var1; } public int getVar2() { return var2; } public int getVar3() { return var3; } public void setVar1(int var1) { this.var1 = var1; } public void setVar2(int var2) { this.var2 = var2; } public void setVar3(int var3) { this.var3 = var3; } } I think the latter type of ordering is clearer both in code and in class diagrams but I do not know if that is enough to rule out the other type of ordering.

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  • extract data from Plist to array and dictionary

    - by Boaz
    Hi I made a plist that looks like that: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList 1.0.dtd"> <plist version="1.0"> <array> <array> <dict> <key>Company</key> <string>xxx</string> <key>Title</key> <string>VP Marketing</string> <key>Name</key> <string>Alon ddfr</string> </dict> <dict> <key>Name</key> <string>Adam Ben Shushan</string> <key>Title</key> <string>CEO</string> <key>Company</key> <string>Shushan ltd.</string> </dict> </array> <array> <dict> <key>Company</key> <string>xxx</string> <key>Title</key> <string>CTO</string> <key>Name</key> <string>Boaz frf</string> </dict> </array> </array> </plist> Now I want to extract the data like that (all the 'A' for key "Name" to one section and all the 'B' "Name" to other one): NSString *plistpath = [[NSBundle mainBundle] pathForResource:@"PeopleData" ofType:@"plist"]; NSMutableArray *attendees = [[NSMutableArray alloc] initWithContentsOfFile:plistpath]; listOfPeople = [[NSMutableArray alloc] init];//Add items NSDictionary *indexADict = [NSDictionary dictionaryWithObject:[[attendees objectAtIndex:0] objectForKey:@"Name"] forKey:@"Profiles"]; NSDictionary *indexBDict = [NSDictionary dictionaryWithObject:[[attendees objectAtIndex:1] objectForKey:@"Name"] forKey:@"Profiles"]; [listOfPeople addObject:indexADict]; [listOfPeople addObject:indexBDict]; This in order to view them in sectioned tableView. I know that the problem is here: NSDictionary *indexADict = [NSDictionary dictionaryWithObject:[[attendees objectAtIndex:0] objectForKey:@"Name"] forKey:@"Profiles"]; But I just can't figure how to do it right. Thanks.

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  • List of Django model instance foreign keys losing consistency during state changes.

    - by Joshua
    I have model, Match, with two foreign keys: class Match(model.Model): winner = models.ForeignKey(Player) loser = models.ForeignKey(Player) When I loop over Match I find that each model instance uses a unique object for the foreign key. This ends up biting me because it introduces inconsistency, here is an example: >>> def print_elo(match_list): ... for match in match_list: ... print match.winner.id, match.winner.elo ... print match.loser.id, match.loser.elo ... >>> print_elo(teacher_match_list) 4 1192.0000000000 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 >>> teacher_match_list[0].winner.elo = 3000 >>> print_elo(teacher_match_list) 4 3000 # Object 4 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 # Object 4 >>> I solved this problem like so: def unify_refrences(match_list): """Makes each unique refrence to a model instance non-unique. In cases where multiple model instances are being used django creates a new object for each model instance, even if it that means creating the same instance twice. If one of these objects has its state changed any other object refrencing the same model instance will not be updated. This method ensure that state changes are seen. It makes sure that variables which hold objects pointing to the same model all hold the same object. Visually this means that a list of [var1, var2] whose internals look like so: var1 --> object1 --> model1 var2 --> object2 --> model1 Will result in the internals being changed so that: var1 --> object1 --> model1 var2 ------^ """ match_dict = {} for match in match_list: try: match.winner = match_dict[match.winner.id] except KeyError: match_dict[match.winner.id] = match.winner try: match.loser = match_dict[match.loser.id] except KeyError: match_dict[match.loser.id] = match.loser My question: Is there a way to solve the problem more elegantly through the use of QuerySets without needing to call save at any point? If not, I'd like to make the solution more generic: how can you get a list of the foreign keys on a model instance or do you have a better generic solution to my problem? Please correct me if you think I don't understand why this is happening.

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  • Hibernate mapping to object that already exists

    - by teehoo
    I have two classes, ServiceType and ServiceRequest. Every ServiceRequest must specify what kind of ServiceType it is. All ServiceType's are predefined in the database, and ServiceRequest is created at runtime by the client. Here are my .hbm files: <hibernate-mapping> <class dynamic-insert="false" dynamic-update="false" mutable="true" name="xxx.model.entity.ServiceRequest" optimistic-lock="version" polymorphism="implicit" select-before-update="false"> <id column="USER_ID" name="id"> <generator class="native"/> </id> <property name="quantity"> <column name="quantity" not-null="true"/> </property> <many-to-one cascade="all" class="xxx.model.entity.ServiceType" column="service_type" name="serviceType" not-null="false" unique="false"/> </class> </hibernate-mapping> and <hibernate-mapping> <class dynamic-insert="false" dynamic-update="false" mutable="true" name="xxx.model.entity.ServiceType" optimistic-lock="version" polymorphism="implicit" select-before-update="false"> <id column="USER_ID" name="id"> <generator class="native"/> </id> <property name="description"> <column name="description" not-null="false"/> </property> <property name="cost"> <column name="cost" not-null="true"/> </property> <property name="enabled"> <column name="enabled" not-null="true"/> </property> </class> </hibernate-mapping> When I run this, I get com.mysql.jdbc.exceptions.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails I think my problem is that when I create a new ServiceRequest object, ServiceType is one of its properties, and therefore when I'm saving ServiceRequest to the database, Hibernate attempts to insert the ServiceType object once again, and finds that it is already exists. If this is the case, how do I make it so that Hibernate points to the exists ServiceType instead of trying to insert it again?

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  • Inheritance of jQuery's prototype partially fails

    - by user1065745
    I want to use Coffeescript to create an UIObject class. This class should inherit from jQuery, so that instances of UIObject can be used as if they where created with jQuery. class UIObject isObject: (val) -> typeof val is "object" constructor: (tag, attributes) -> @merge jQuery(tag, attributes), this @UIObjectProperties = {} merge: (source, destination) -> for key of source if destination[key] is undefined destination[key] = source[key] else if @isObject(source[key]) @merge(source[key], destination[key]) return It partially works. Consider the Foobar class below: class Foobar extends UIObject constructor: -> super("<h1/>", html: "Foobar") $("body").append(new Foobar) works fine. BUT: (new Foobar).appendTo("body") places the tag, but also raises RangeError: Maximum call stack size exceeded. Was it just a bad idea to inherit from jQuery? Or is there a solurion? For those who don't know CoffeeScript, the JavaScript source is: var Foobar, UIObject; var __hasProp = Object.prototype.hasOwnProperty, __extends = function(child, parent) { for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor; child.__super__ = parent.prototype; return child; }; UIObject = (function () { UIObject.prototype.isObject = function (val) { return typeof val === "object"; }; function UIObject(tag, attributes) { this.merge(jQuery(tag, attributes), this); this.UIObjectProperties = {}; } UIObject.prototype.merge = function (source, destination) { var key; for (key in source) { if (destination[key] === void 0) { destination[key] = source[key]; } else if (this.isObject(source[key])) { this.merge(source[key], destination[key]); } } }; return UIObject; })(); Foobar = (function () { __extends(Foobar, UIObject); function Foobar() { Foobar.__super__.constructor.call(this, "<h1/>", { html: "Foobar" }); } return Foobar; })();

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  • Maintaining shared service in ASP.NET MVC Application

    - by kazimanzurrashid
    Depending on the application sometimes we have to maintain some shared service throughout our application. Let’s say you are developing a multi-blog supported blog engine where both the controller and view must know the currently visiting blog, it’s setting , user information and url generation service. In this post, I will show you how you can handle this kind of case in most convenient way. First, let see the most basic way, we can create our PostController in the following way: public class PostController : Controller { public PostController(dependencies...) { } public ActionResult Index(string blogName, int? page) { BlogInfo blog = blogSerivce.FindByName(blogName); if (blog == null) { return new NotFoundResult(); } IEnumerable<PostInfo> posts = postService.FindPublished(blog.Id, PagingCalculator.StartIndex(page, blog.PostPerPage), blog.PostPerPage); int count = postService.GetPublishedCount(blog.Id); UserInfo user = null; if (HttpContext.User.Identity.IsAuthenticated) { user = userService.FindByName(HttpContext.User.Identity.Name); } return View(new IndexViewModel(urlResolver, user, blog, posts, count, page)); } public ActionResult Archive(string blogName, int? page, ArchiveDate archiveDate) { BlogInfo blog = blogSerivce.FindByName(blogName); if (blog == null) { return new NotFoundResult(); } IEnumerable<PostInfo> posts = postService.FindArchived(blog.Id, archiveDate, PagingCalculator.StartIndex(page, blog.PostPerPage), blog.PostPerPage); int count = postService.GetArchivedCount(blog.Id, archiveDate); UserInfo user = null; if (HttpContext.User.Identity.IsAuthenticated) { user = userService.FindByName(HttpContext.User.Identity.Name); } return View(new ArchiveViewModel(urlResolver, user, blog, posts, count, page, achiveDate)); } public ActionResult Tag(string blogName, string tagSlug, int? page) { BlogInfo blog = blogSerivce.FindByName(blogName); if (blog == null) { return new NotFoundResult(); } TagInfo tag = tagService.FindBySlug(blog.Id, tagSlug); if (tag == null) { return new NotFoundResult(); } IEnumerable<PostInfo> posts = postService.FindPublishedByTag(blog.Id, tag.Id, PagingCalculator.StartIndex(page, blog.PostPerPage), blog.PostPerPage); int count = postService.GetPublishedCountByTag(tag.Id); UserInfo user = null; if (HttpContext.User.Identity.IsAuthenticated) { user = userService.FindByName(HttpContext.User.Identity.Name); } return View(new TagViewModel(urlResolver, user, blog, posts, count, page, tag)); } } As you can see the above code heavily depends upon the current blog and the blog retrieval code is duplicated in all of the action methods, once the blog is retrieved the same blog is passed in the view model. Other than the blog the view also needs the current user and url resolver to render it properly. One way to remove the duplicate blog retrieval code is to create a custom model binder which converts the blog from a blog name and use the blog a parameter in the action methods instead of the string blog name, but it only helps the first half in the above scenario, the action methods still have to pass the blog, user and url resolver etc in the view model. Now lets try to improve the the above code, first lets create a new class which would contain the shared services, lets name it as BlogContext: public class BlogContext { public BlogInfo Blog { get; set; } public UserInfo User { get; set; } public IUrlResolver UrlResolver { get; set; } } Next, we will create an interface, IContextAwareService: public interface IContextAwareService { BlogContext Context { get; set; } } The idea is, whoever needs these shared services needs to implement this interface, in our case both the controller and the view model, now we will create an action filter which will be responsible for populating the context: public class PopulateBlogContextAttribute : FilterAttribute, IActionFilter { private static string blogNameRouteParameter = "blogName"; private readonly IBlogService blogService; private readonly IUserService userService; private readonly BlogContext context; public PopulateBlogContextAttribute(IBlogService blogService, IUserService userService, IUrlResolver urlResolver) { Invariant.IsNotNull(blogService, "blogService"); Invariant.IsNotNull(userService, "userService"); Invariant.IsNotNull(urlResolver, "urlResolver"); this.blogService = blogService; this.userService = userService; context = new BlogContext { UrlResolver = urlResolver }; } public static string BlogNameRouteParameter { [DebuggerStepThrough] get { return blogNameRouteParameter; } [DebuggerStepThrough] set { blogNameRouteParameter = value; } } public void OnActionExecuting(ActionExecutingContext filterContext) { string blogName = (string) filterContext.Controller.ValueProvider.GetValue(BlogNameRouteParameter).ConvertTo(typeof(string), Culture.Current); if (!string.IsNullOrWhiteSpace(blogName)) { context.Blog = blogService.FindByName(blogName); } if (context.Blog == null) { filterContext.Result = new NotFoundResult(); return; } if (filterContext.HttpContext.User.Identity.IsAuthenticated) { context.User = userService.FindByName(filterContext.HttpContext.User.Identity.Name); } IContextAwareService controller = filterContext.Controller as IContextAwareService; if (controller != null) { controller.Context = context; } } public void OnActionExecuted(ActionExecutedContext filterContext) { Invariant.IsNotNull(filterContext, "filterContext"); if ((filterContext.Exception == null) || filterContext.ExceptionHandled) { IContextAwareService model = filterContext.Controller.ViewData.Model as IContextAwareService; if (model != null) { model.Context = context; } } } } As you can see we are populating the context in the OnActionExecuting, which executes just before the controllers action methods executes, so by the time our action methods executes the context is already populated, next we are are assigning the same context in the view model in OnActionExecuted method which executes just after we set the  model and return the view in our action methods. Now, lets change the view models so that it implements this interface: public class IndexViewModel : IContextAwareService { // More Codes } public class ArchiveViewModel : IContextAwareService { // More Codes } public class TagViewModel : IContextAwareService { // More Codes } and the controller: public class PostController : Controller, IContextAwareService { public PostController(dependencies...) { } public BlogContext Context { get; set; } public ActionResult Index(int? page) { IEnumerable<PostInfo> posts = postService.FindPublished(Context.Blog.Id, PagingCalculator.StartIndex(page, Context.Blog.PostPerPage), Context.Blog.PostPerPage); int count = postService.GetPublishedCount(Context.Blog.Id); return View(new IndexViewModel(posts, count, page)); } public ActionResult Archive(int? page, ArchiveDate archiveDate) { IEnumerable<PostInfo> posts = postService.FindArchived(Context.Blog.Id, archiveDate, PagingCalculator.StartIndex(page, Context.Blog.PostPerPage), Context.Blog.PostPerPage); int count = postService.GetArchivedCount(Context.Blog.Id, archiveDate); return View(new ArchiveViewModel(posts, count, page, achiveDate)); } public ActionResult Tag(string blogName, string tagSlug, int? page) { TagInfo tag = tagService.FindBySlug(Context.Blog.Id, tagSlug); if (tag == null) { return new NotFoundResult(); } IEnumerable<PostInfo> posts = postService.FindPublishedByTag(Context.Blog.Id, tag.Id, PagingCalculator.StartIndex(page, Context.Blog.PostPerPage), Context.Blog.PostPerPage); int count = postService.GetPublishedCountByTag(tag.Id); return View(new TagViewModel(posts, count, page, tag)); } } Now, the last thing where we have to glue everything, I will be using the AspNetMvcExtensibility to register the action filter (as there is no better way to inject the dependencies in action filters). public class RegisterFilters : RegisterFiltersBase { private static readonly Type controllerType = typeof(Controller); private static readonly Type contextAwareType = typeof(IContextAwareService); protected override void Register(IFilterRegistry registry) { TypeCatalog controllers = new TypeCatalogBuilder() .Add(GetType().Assembly) .Include(type => controllerType.IsAssignableFrom(type) && contextAwareType.IsAssignableFrom(type)); registry.Register<PopulateBlogContextAttribute>(controllers); } } Thoughts and Comments?

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  • value types in the vm

    - by john.rose
    value types in the vm p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} p.p2 {margin: 0.0px 0.0px 14.0px 0.0px; font: 14.0px Times} p.p3 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times} p.p4 {margin: 0.0px 0.0px 15.0px 0.0px; font: 14.0px Times} p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier} p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier; min-height: 17.0px} p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p8 {margin: 0.0px 0.0px 0.0px 36.0px; text-indent: -36.0px; font: 14.0px Times; min-height: 18.0px} p.p9 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p10 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; color: #000000} li.li1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} li.li7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} span.s1 {font: 14.0px Courier} span.s2 {color: #000000} span.s3 {font: 14.0px Courier; color: #000000} ol.ol1 {list-style-type: decimal} Or, enduring values for a changing world. Introduction A value type is a data type which, generally speaking, is designed for being passed by value in and out of methods, and stored by value in data structures. The only value types which the Java language directly supports are the eight primitive types. Java indirectly and approximately supports value types, if they are implemented in terms of classes. For example, both Integer and String may be viewed as value types, especially if their usage is restricted to avoid operations appropriate to Object. In this note, we propose a definition of value types in terms of a design pattern for Java classes, accompanied by a set of usage restrictions. We also sketch the relation of such value types to tuple types (which are a JVM-level notion), and point out JVM optimizations that can apply to value types. This note is a thought experiment to extend the JVM’s performance model in support of value types. The demonstration has two phases.  Initially the extension can simply use design patterns, within the current bytecode architecture, and in today’s Java language. But if the performance model is to be realized in practice, it will probably require new JVM bytecode features, changes to the Java language, or both.  We will look at a few possibilities for these new features. An Axiom of Value In the context of the JVM, a value type is a data type equipped with construction, assignment, and equality operations, and a set of typed components, such that, whenever two variables of the value type produce equal corresponding values for their components, the values of the two variables cannot be distinguished by any JVM operation. Here are some corollaries: A value type is immutable, since otherwise a copy could be constructed and the original could be modified in one of its components, allowing the copies to be distinguished. Changing the component of a value type requires construction of a new value. The equals and hashCode operations are strictly component-wise. If a value type is represented by a JVM reference, that reference cannot be successfully synchronized on, and cannot be usefully compared for reference equality. A value type can be viewed in terms of what it doesn’t do. We can say that a value type omits all value-unsafe operations, which could violate the constraints on value types.  These operations, which are ordinarily allowed for Java object types, are pointer equality comparison (the acmp instruction), synchronization (the monitor instructions), all the wait and notify methods of class Object, and non-trivial finalize methods. The clone method is also value-unsafe, although for value types it could be treated as the identity function. Finally, and most importantly, any side effect on an object (however visible) also counts as an value-unsafe operation. A value type may have methods, but such methods must not change the components of the value. It is reasonable and useful to define methods like toString, equals, and hashCode on value types, and also methods which are specifically valuable to users of the value type. Representations of Value Value types have two natural representations in the JVM, unboxed and boxed. An unboxed value consists of the components, as simple variables. For example, the complex number x=(1+2i), in rectangular coordinate form, may be represented in unboxed form by the following pair of variables: /*Complex x = Complex.valueOf(1.0, 2.0):*/ double x_re = 1.0, x_im = 2.0; These variables might be locals, parameters, or fields. Their association as components of a single value is not defined to the JVM. Here is a sample computation which computes the norm of the difference between two complex numbers: double distance(/*Complex x:*/ double x_re, double x_im,         /*Complex y:*/ double y_re, double y_im) {     /*Complex z = x.minus(y):*/     double z_re = x_re - y_re, z_im = x_im - y_im;     /*return z.abs():*/     return Math.sqrt(z_re*z_re + z_im*z_im); } A boxed representation groups component values under a single object reference. The reference is to a ‘wrapper class’ that carries the component values in its fields. (A primitive type can naturally be equated with a trivial value type with just one component of that type. In that view, the wrapper class Integer can serve as a boxed representation of value type int.) The unboxed representation of complex numbers is practical for many uses, but it fails to cover several major use cases: return values, array elements, and generic APIs. The two components of a complex number cannot be directly returned from a Java function, since Java does not support multiple return values. The same story applies to array elements: Java has no ’array of structs’ feature. (Double-length arrays are a possible workaround for complex numbers, but not for value types with heterogeneous components.) By generic APIs I mean both those which use generic types, like Arrays.asList and those which have special case support for primitive types, like String.valueOf and PrintStream.println. Those APIs do not support unboxed values, and offer some problems to boxed values. Any ’real’ JVM type should have a story for returns, arrays, and API interoperability. The basic problem here is that value types fall between primitive types and object types. Value types are clearly more complex than primitive types, and object types are slightly too complicated. Objects are a little bit dangerous to use as value carriers, since object references can be compared for pointer equality, and can be synchronized on. Also, as many Java programmers have observed, there is often a performance cost to using wrapper objects, even on modern JVMs. Even so, wrapper classes are a good starting point for talking about value types. If there were a set of structural rules and restrictions which would prevent value-unsafe operations on value types, wrapper classes would provide a good notation for defining value types. This note attempts to define such rules and restrictions. Let’s Start Coding Now it is time to look at some real code. Here is a definition, written in Java, of a complex number value type. @ValueSafe public final class Complex implements java.io.Serializable {     // immutable component structure:     public final double re, im;     private Complex(double re, double im) {         this.re = re; this.im = im;     }     // interoperability methods:     public String toString() { return "Complex("+re+","+im+")"; }     public List<Double> asList() { return Arrays.asList(re, im); }     public boolean equals(Complex c) {         return re == c.re && im == c.im;     }     public boolean equals(@ValueSafe Object x) {         return x instanceof Complex && equals((Complex) x);     }     public int hashCode() {         return 31*Double.valueOf(re).hashCode()                 + Double.valueOf(im).hashCode();     }     // factory methods:     public static Complex valueOf(double re, double im) {         return new Complex(re, im);     }     public Complex changeRe(double re2) { return valueOf(re2, im); }     public Complex changeIm(double im2) { return valueOf(re, im2); }     public static Complex cast(@ValueSafe Object x) {         return x == null ? ZERO : (Complex) x;     }     // utility methods and constants:     public Complex plus(Complex c)  { return new Complex(re+c.re, im+c.im); }     public Complex minus(Complex c) { return new Complex(re-c.re, im-c.im); }     public double abs() { return Math.sqrt(re*re + im*im); }     public static final Complex PI = valueOf(Math.PI, 0.0);     public static final Complex ZERO = valueOf(0.0, 0.0); } This is not a minimal definition, because it includes some utility methods and other optional parts.  The essential elements are as follows: The class is marked as a value type with an annotation. The class is final, because it does not make sense to create subclasses of value types. The fields of the class are all non-private and final.  (I.e., the type is immutable and structurally transparent.) From the supertype Object, all public non-final methods are overridden. The constructor is private. Beyond these bare essentials, we can observe the following features in this example, which are likely to be typical of all value types: One or more factory methods are responsible for value creation, including a component-wise valueOf method. There are utility methods for complex arithmetic and instance creation, such as plus and changeIm. There are static utility constants, such as PI. The type is serializable, using the default mechanisms. There are methods for converting to and from dynamically typed references, such as asList and cast. The Rules In order to use value types properly, the programmer must avoid value-unsafe operations.  A helpful Java compiler should issue errors (or at least warnings) for code which provably applies value-unsafe operations, and should issue warnings for code which might be correct but does not provably avoid value-unsafe operations.  No such compilers exist today, but to simplify our account here, we will pretend that they do exist. A value-safe type is any class, interface, or type parameter marked with the @ValueSafe annotation, or any subtype of a value-safe type.  If a value-safe class is marked final, it is in fact a value type.  All other value-safe classes must be abstract.  The non-static fields of a value class must be non-public and final, and all its constructors must be private. Under the above rules, a standard interface could be helpful to define value types like Complex.  Here is an example: @ValueSafe public interface ValueType extends java.io.Serializable {     // All methods listed here must get redefined.     // Definitions must be value-safe, which means     // they may depend on component values only.     List<? extends Object> asList();     int hashCode();     boolean equals(@ValueSafe Object c);     String toString(); } //@ValueSafe inherited from supertype: public final class Complex implements ValueType { … The main advantage of such a conventional interface is that (unlike an annotation) it is reified in the runtime type system.  It could appear as an element type or parameter bound, for facilities which are designed to work on value types only.  More broadly, it might assist the JVM to perform dynamic enforcement of the rules for value types. Besides types, the annotation @ValueSafe can mark fields, parameters, local variables, and methods.  (This is redundant when the type is also value-safe, but may be useful when the type is Object or another supertype of a value type.)  Working forward from these annotations, an expression E is defined as value-safe if it satisfies one or more of the following: The type of E is a value-safe type. E names a field, parameter, or local variable whose declaration is marked @ValueSafe. E is a call to a method whose declaration is marked @ValueSafe. E is an assignment to a value-safe variable, field reference, or array reference. E is a cast to a value-safe type from a value-safe expression. E is a conditional expression E0 ? E1 : E2, and both E1 and E2 are value-safe. Assignments to value-safe expressions and initializations of value-safe names must take their values from value-safe expressions. A value-safe expression may not be the subject of a value-unsafe operation.  In particular, it cannot be synchronized on, nor can it be compared with the “==” operator, not even with a null or with another value-safe type. In a program where all of these rules are followed, no value-type value will be subject to a value-unsafe operation.  Thus, the prime axiom of value types will be satisfied, that no two value type will be distinguishable as long as their component values are equal. More Code To illustrate these rules, here are some usage examples for Complex: Complex pi = Complex.valueOf(Math.PI, 0); Complex zero = pi.changeRe(0);  //zero = pi; zero.re = 0; ValueType vtype = pi; @SuppressWarnings("value-unsafe")   Object obj = pi; @ValueSafe Object obj2 = pi; obj2 = new Object();  // ok List<Complex> clist = new ArrayList<Complex>(); clist.add(pi);  // (ok assuming List.add param is @ValueSafe) List<ValueType> vlist = new ArrayList<ValueType>(); vlist.add(pi);  // (ok) List<Object> olist = new ArrayList<Object>(); olist.add(pi);  // warning: "value-unsafe" boolean z = pi.equals(zero); boolean z1 = (pi == zero);  // error: reference comparison on value type boolean z2 = (pi == null);  // error: reference comparison on value type boolean z3 = (pi == obj2);  // error: reference comparison on value type synchronized (pi) { }  // error: synch of value, unpredictable result synchronized (obj2) { }  // unpredictable result Complex qq = pi; qq = null;  // possible NPE; warning: “null-unsafe" qq = (Complex) obj;  // warning: “null-unsafe" qq = Complex.cast(obj);  // OK @SuppressWarnings("null-unsafe")   Complex empty = null;  // possible NPE qq = empty;  // possible NPE (null pollution) The Payoffs It follows from this that either the JVM or the java compiler can replace boxed value-type values with unboxed ones, without affecting normal computations.  Fields and variables of value types can be split into their unboxed components.  Non-static methods on value types can be transformed into static methods which take the components as value parameters. Some common questions arise around this point in any discussion of value types. Why burden the programmer with all these extra rules?  Why not detect programs automagically and perform unboxing transparently?  The answer is that it is easy to break the rules accidently unless they are agreed to by the programmer and enforced.  Automatic unboxing optimizations are tantalizing but (so far) unreachable ideal.  In the current state of the art, it is possible exhibit benchmarks in which automatic unboxing provides the desired effects, but it is not possible to provide a JVM with a performance model that assures the programmer when unboxing will occur.  This is why I’m writing this note, to enlist help from, and provide assurances to, the programmer.  Basically, I’m shooting for a good set of user-supplied “pragmas” to frame the desired optimization. Again, the important thing is that the unboxing must be done reliably, or else programmers will have no reason to work with the extra complexity of the value-safety rules.  There must be a reasonably stable performance model, wherein using a value type has approximately the same performance characteristics as writing the unboxed components as separate Java variables. There are some rough corners to the present scheme.  Since Java fields and array elements are initialized to null, value-type computations which incorporate uninitialized variables can produce null pointer exceptions.  One workaround for this is to require such variables to be null-tested, and the result replaced with a suitable all-zero value of the value type.  That is what the “cast” method does above. Generically typed APIs like List<T> will continue to manipulate boxed values always, at least until we figure out how to do reification of generic type instances.  Use of such APIs will elicit warnings until their type parameters (and/or relevant members) are annotated or typed as value-safe.  Retrofitting List<T> is likely to expose flaws in the present scheme, which we will need to engineer around.  Here are a couple of first approaches: public interface java.util.List<@ValueSafe T> extends Collection<T> { … public interface java.util.List<T extends Object|ValueType> extends Collection<T> { … (The second approach would require disjunctive types, in which value-safety is “contagious” from the constituent types.) With more transformations, the return value types of methods can also be unboxed.  This may require significant bytecode-level transformations, and would work best in the presence of a bytecode representation for multiple value groups, which I have proposed elsewhere under the title “Tuples in the VM”. But for starters, the JVM can apply this transformation under the covers, to internally compiled methods.  This would give a way to express multiple return values and structured return values, which is a significant pain-point for Java programmers, especially those who work with low-level structure types favored by modern vector and graphics processors.  The lack of multiple return values has a strong distorting effect on many Java APIs. Even if the JVM fails to unbox a value, there is still potential benefit to the value type.  Clustered computing systems something have copy operations (serialization or something similar) which apply implicitly to command operands.  When copying JVM objects, it is extremely helpful to know when an object’s identity is important or not.  If an object reference is a copied operand, the system may have to create a proxy handle which points back to the original object, so that side effects are visible.  Proxies must be managed carefully, and this can be expensive.  On the other hand, value types are exactly those types which a JVM can “copy and forget” with no downside. Array types are crucial to bulk data interfaces.  (As data sizes and rates increase, bulk data becomes more important than scalar data, so arrays are definitely accompanying us into the future of computing.)  Value types are very helpful for adding structure to bulk data, so a successful value type mechanism will make it easier for us to express richer forms of bulk data. Unboxing arrays (i.e., arrays containing unboxed values) will provide better cache and memory density, and more direct data movement within clustered or heterogeneous computing systems.  They require the deepest transformations, relative to today’s JVM.  There is an impedance mismatch between value-type arrays and Java’s covariant array typing, so compromises will need to be struck with existing Java semantics.  It is probably worth the effort, since arrays of unboxed value types are inherently more memory-efficient than standard Java arrays, which rely on dependent pointer chains. It may be sufficient to extend the “value-safe” concept to array declarations, and allow low-level transformations to change value-safe array declarations from the standard boxed form into an unboxed tuple-based form.  Such value-safe arrays would not be convertible to Object[] arrays.  Certain connection points, such as Arrays.copyOf and System.arraycopy might need additional input/output combinations, to allow smooth conversion between arrays with boxed and unboxed elements. Alternatively, the correct solution may have to wait until we have enough reification of generic types, and enough operator overloading, to enable an overhaul of Java arrays. Implicit Method Definitions The example of class Complex above may be unattractively complex.  I believe most or all of the elements of the example class are required by the logic of value types. If this is true, a programmer who writes a value type will have to write lots of error-prone boilerplate code.  On the other hand, I think nearly all of the code (except for the domain-specific parts like plus and minus) can be implicitly generated. Java has a rule for implicitly defining a class’s constructor, if no it defines no constructors explicitly.  Likewise, there are rules for providing default access modifiers for interface members.  Because of the highly regular structure of value types, it might be reasonable to perform similar implicit transformations on value types.  Here’s an example of a “highly implicit” definition of a complex number type: public class Complex implements ValueType {  // implicitly final     public double re, im;  // implicitly public final     //implicit methods are defined elementwise from te fields:     //  toString, asList, equals(2), hashCode, valueOf, cast     //optionally, explicit methods (plus, abs, etc.) would go here } In other words, with the right defaults, a simple value type definition can be a one-liner.  The observant reader will have noticed the similarities (and suitable differences) between the explicit methods above and the corresponding methods for List<T>. Another way to abbreviate such a class would be to make an annotation the primary trigger of the functionality, and to add the interface(s) implicitly: public @ValueType class Complex { … // implicitly final, implements ValueType (But to me it seems better to communicate the “magic” via an interface, even if it is rooted in an annotation.) Implicitly Defined Value Types So far we have been working with nominal value types, which is to say that the sequence of typed components is associated with a name and additional methods that convey the intention of the programmer.  A simple ordered pair of floating point numbers can be variously interpreted as (to name a few possibilities) a rectangular or polar complex number or Cartesian point.  The name and the methods convey the intended meaning. But what if we need a truly simple ordered pair of floating point numbers, without any further conceptual baggage?  Perhaps we are writing a method (like “divideAndRemainder”) which naturally returns a pair of numbers instead of a single number.  Wrapping the pair of numbers in a nominal type (like “QuotientAndRemainder”) makes as little sense as wrapping a single return value in a nominal type (like “Quotient”).  What we need here are structural value types commonly known as tuples. For the present discussion, let us assign a conventional, JVM-friendly name to tuples, roughly as follows: public class java.lang.tuple.$DD extends java.lang.tuple.Tuple {      double $1, $2; } Here the component names are fixed and all the required methods are defined implicitly.  The supertype is an abstract class which has suitable shared declarations.  The name itself mentions a JVM-style method parameter descriptor, which may be “cracked” to determine the number and types of the component fields. The odd thing about such a tuple type (and structural types in general) is it must be instantiated lazily, in response to linkage requests from one or more classes that need it.  The JVM and/or its class loaders must be prepared to spin a tuple type on demand, given a simple name reference, $xyz, where the xyz is cracked into a series of component types.  (Specifics of naming and name mangling need some tasteful engineering.) Tuples also seem to demand, even more than nominal types, some support from the language.  (This is probably because notations for non-nominal types work best as combinations of punctuation and type names, rather than named constructors like Function3 or Tuple2.)  At a minimum, languages with tuples usually (I think) have some sort of simple bracket notation for creating tuples, and a corresponding pattern-matching syntax (or “destructuring bind”) for taking tuples apart, at least when they are parameter lists.  Designing such a syntax is no simple thing, because it ought to play well with nominal value types, and also with pre-existing Java features, such as method parameter lists, implicit conversions, generic types, and reflection.  That is a task for another day. Other Use Cases Besides complex numbers and simple tuples there are many use cases for value types.  Many tuple-like types have natural value-type representations. These include rational numbers, point locations and pixel colors, and various kinds of dates and addresses. Other types have a variable-length ‘tail’ of internal values. The most common example of this is String, which is (mathematically) a sequence of UTF-16 character values. Similarly, bit vectors, multiple-precision numbers, and polynomials are composed of sequences of values. Such types include, in their representation, a reference to a variable-sized data structure (often an array) which (somehow) represents the sequence of values. The value type may also include ’header’ information. Variable-sized values often have a length distribution which favors short lengths. In that case, the design of the value type can make the first few values in the sequence be direct ’header’ fields of the value type. In the common case where the header is enough to represent the whole value, the tail can be a shared null value, or even just a null reference. Note that the tail need not be an immutable object, as long as the header type encapsulates it well enough. This is the case with String, where the tail is a mutable (but never mutated) character array. Field types and their order must be a globally visible part of the API.  The structure of the value type must be transparent enough to have a globally consistent unboxed representation, so that all callers and callees agree about the type and order of components  that appear as parameters, return types, and array elements.  This is a trade-off between efficiency and encapsulation, which is forced on us when we remove an indirection enjoyed by boxed representations.  A JVM-only transformation would not care about such visibility, but a bytecode transformation would need to take care that (say) the components of complex numbers would not get swapped after a redefinition of Complex and a partial recompile.  Perhaps constant pool references to value types need to declare the field order as assumed by each API user. This brings up the delicate status of private fields in a value type.  It must always be possible to load, store, and copy value types as coordinated groups, and the JVM performs those movements by moving individual scalar values between locals and stack.  If a component field is not public, what is to prevent hostile code from plucking it out of the tuple using a rogue aload or astore instruction?  Nothing but the verifier, so we may need to give it more smarts, so that it treats value types as inseparable groups of stack slots or locals (something like long or double). My initial thought was to make the fields always public, which would make the security problem moot.  But public is not always the right answer; consider the case of String, where the underlying mutable character array must be encapsulated to prevent security holes.  I believe we can win back both sides of the tradeoff, by training the verifier never to split up the components in an unboxed value.  Just as the verifier encapsulates the two halves of a 64-bit primitive, it can encapsulate the the header and body of an unboxed String, so that no code other than that of class String itself can take apart the values. Similar to String, we could build an efficient multi-precision decimal type along these lines: public final class DecimalValue extends ValueType {     protected final long header;     protected private final BigInteger digits;     public DecimalValue valueOf(int value, int scale) {         assert(scale >= 0);         return new DecimalValue(((long)value << 32) + scale, null);     }     public DecimalValue valueOf(long value, int scale) {         if (value == (int) value)             return valueOf((int)value, scale);         return new DecimalValue(-scale, new BigInteger(value));     } } Values of this type would be passed between methods as two machine words. Small values (those with a significand which fits into 32 bits) would be represented without any heap data at all, unless the DecimalValue itself were boxed. (Note the tension between encapsulation and unboxing in this case.  It would be better if the header and digits fields were private, but depending on where the unboxing information must “leak”, it is probably safer to make a public revelation of the internal structure.) Note that, although an array of Complex can be faked with a double-length array of double, there is no easy way to fake an array of unboxed DecimalValues.  (Either an array of boxed values or a transposed pair of homogeneous arrays would be reasonable fallbacks, in a current JVM.)  Getting the full benefit of unboxing and arrays will require some new JVM magic. Although the JVM emphasizes portability, system dependent code will benefit from using machine-level types larger than 64 bits.  For example, the back end of a linear algebra package might benefit from value types like Float4 which map to stock vector types.  This is probably only worthwhile if the unboxing arrays can be packed with such values. More Daydreams A more finely-divided design for dynamic enforcement of value safety could feature separate marker interfaces for each invariant.  An empty marker interface Unsynchronizable could cause suitable exceptions for monitor instructions on objects in marked classes.  More radically, a Interchangeable marker interface could cause JVM primitives that are sensitive to object identity to raise exceptions; the strangest result would be that the acmp instruction would have to be specified as raising an exception. @ValueSafe public interface ValueType extends java.io.Serializable,         Unsynchronizable, Interchangeable { … public class Complex implements ValueType {     // inherits Serializable, Unsynchronizable, Interchangeable, @ValueSafe     … It seems possible that Integer and the other wrapper types could be retro-fitted as value-safe types.  This is a major change, since wrapper objects would be unsynchronizable and their references interchangeable.  It is likely that code which violates value-safety for wrapper types exists but is uncommon.  It is less plausible to retro-fit String, since the prominent operation String.intern is often used with value-unsafe code. We should also reconsider the distinction between boxed and unboxed values in code.  The design presented above obscures that distinction.  As another thought experiment, we could imagine making a first class distinction in the type system between boxed and unboxed representations.  Since only primitive types are named with a lower-case initial letter, we could define that the capitalized version of a value type name always refers to the boxed representation, while the initial lower-case variant always refers to boxed.  For example: complex pi = complex.valueOf(Math.PI, 0); Complex boxPi = pi;  // convert to boxed myList.add(boxPi); complex z = myList.get(0);  // unbox Such a convention could perhaps absorb the current difference between int and Integer, double and Double. It might also allow the programmer to express a helpful distinction among array types. As said above, array types are crucial to bulk data interfaces, but are limited in the JVM.  Extending arrays beyond the present limitations is worth thinking about; for example, the Maxine JVM implementation has a hybrid object/array type.  Something like this which can also accommodate value type components seems worthwhile.  On the other hand, does it make sense for value types to contain short arrays?  And why should random-access arrays be the end of our design process, when bulk data is often sequentially accessed, and it might make sense to have heterogeneous streams of data as the natural “jumbo” data structure.  These considerations must wait for another day and another note. More Work It seems to me that a good sequence for introducing such value types would be as follows: Add the value-safety restrictions to an experimental version of javac. Code some sample applications with value types, including Complex and DecimalValue. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. A staggered roll-out like this would decouple language changes from bytecode changes, which is always a convenient thing. A similar investigation should be applied (concurrently) to array types.  In this case, it seems to me that the starting point is in the JVM: Add an experimental unboxing array data structure to a production JVM, perhaps along the lines of Maxine hybrids.  No bytecode or language support is required at first; everything can be done with encapsulated unsafe operations and/or method handles. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. That’s enough musing me for now.  Back to work!

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