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Beginning Haskell: "not in scope" Unprecedented error

- by user1071838

So I just started learning Haskell, and this (http://learnyouahaskell.com) nifty book is giving a lot of help. So yesterday I wrote in a text file doubleMe x = x + x and saved it as double.hs. So after saving that I open up my command prompt, CD to the right folder, type in "ghci" to get haskell started, and then type in >doubleMe 5 10 and everything seems to work. Now today, I do the same thing and this happens (actual copy paste from command line) . . . C:\Users\myName\haskell>ghci GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :l double.hs [1 of 1] Compiling Main ( double.hs, interpreted ) Ok, modules loaded: Main. *Main> doubleMe 5 <interactive>:1:1: Not in scope: `doubleMe' So basically, everything was working fine, but now haskell can't find the function I wrote in double.hs. Can anyone tell what is going on? I'm pretty lost and confused. This is just a guess but does it have to do with *Main at all? Thanks for the help.

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Potential g++ template bug?

- by Evan Teran

I've encountered some code which I think should compile, but doesn't. So I'm hoping some of the local standards experts here at SO can help :-). I basically have some code which resembles this: #include <iostream> template <class T = int> class A { public: class U { }; public: U f() const { return U(); } }; // test either the work around or the code I want... #ifndef USE_FIX template <class T> bool operator==(const typename A<T>::U &x, int y) { return true; } #else typedef A<int> AI; bool operator==(const AI::U &x, int y) { return true; } #endif int main() { A<int> a; std::cout << (a.f() == 1) << std::endl; } So, to describe what is going on here. I have a class template (A) which has an internal class (U) and at least one member function which can return an instance of that internal class (f()). Then I am attempting to create an operator== function which compares this internal type to some other type (in this case an int, but it doesn't seem to matter). When USE_FIX is not defined I get the following error: test.cc: In function 'int main()': test.cc:27:25: error: no match for 'operator==' in 'a.A<T>::f [with T = int]() == 1' Which seems odd, because I am clearly (I think) defining a templated operator== which should cover this, in fact if I just do a little of the work for the compiler (enable USE_FIX), then I no longer get an error. Unfortunately, the "fix" doesn't work generically, only for a specific instantiation of the template. Is this supposed to work as I expected? Or is this simply not allowed? BTW: if it matters I am using gcc 4.5.2.

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StructureMap and injecting IEnumerable<T>

- by GiddyUpHorsey

I'm new to StructureMap and have some existing code that I'm working with that uses StructureMap 2.5.4. There is a class that is constructed using StructureMap that has a constructor that takes IEnumerable<TCar> as a parameter. The registry has the following code. Scan(x => { x.TheCallingAssembly(); x.WithDefaultConventions(); x.AddAllTypesOf<ICar>(); } ); ForRequestedType<IEnumerable<ICar>>().TheDefault.Is.ConstructedBy( x => ObjectFactory.GetAllInstances<ICar>()); I'm writing a unit test and have obtained a nested container off the ObjectFactory and have injected an instance using the Inject method. One of the instances of ICar should receive the injected type in its constructor. However it wasn't working and I tracked that down to the ObjectFactory.GetAllInstances() call which doesn't use my nested container. How can I get this to work? I also read about StructureMap autowiring arrays and IEnumerable instances but I couldn't get it to work. Is there a better way to rewrite the above registry code so that an instance of IEnumerable<TCar> will be created and use the injected type from my nested container?

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jquery image fading with tabs

- by StealthRT

Hey all, i am trying my best to figure out how to go about doing this: I have 2 tabs. When the page loads tab1 is selected automatically. This shows the tab as 1.0 transparency while tab2 stays at 0.7. Once the user clicks on tab2, tab1 goes to 0.7 transparency and tab2 goes to 1.0. However, i can not seem to get it to do that! Here is my code: <script type="text/javascript"> function checkTab(theTab) { $('#tab1').fadeTo(250, 0.70); $('#tab2').fadeTo(250, 0.70); if ($("#tabActive").val() == theTab) { $(theTab).fadeTo(250, 1); } } $(document).ready(function() { $('#tab1').hover(function() {$(this).fadeTo(250, 1)}, function() {checkTab('#tab1')}); $('#tab2').hover(function() {$(this).fadeTo(250, 1)}, function() {checkTab('#tab2')}); $('#tab2').fadeTo(250, 0.70); $('#tabActive').val('tab1'); }); </script> <li class="stats"><img src="images/Stats.png" name="nav1" width="70" height="52" id="tab1" onclick="$('#tabActive').val('tab1');" /></li> <li class="cal"><img src="images/cal.png" name="nav1" width="70" height="52" id="tab2" onclick="$('#tabActive').val('tab2');" /></li> <input name="tabActive" id="tabActive" type="text" /> Any help would be great! :) David

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SQLce DAL Linq to Sql or EntityFramework

- by bretddog

Hi, I'm learning databases, using SqlCe, and need business object to database mapping. Currently I try to decide if to use Linq to Sql, or EntityFramework. (I understand a bit L2S, but haven't familiarized with EF yet) The program will only be debeloped and used by myself, so I have good control of the priorities: I don't need to consider potential change of database type or data storage type, as I'm quite certain SQLce will stay sufficient. I DO expect continued development and changes to the data scheme while the program is in active use; change business object properties (Hence database columns), and possibly overall table scheme. So old data must be transported to new scheme. I also want to keep a decent degree of layer separation DAL/BLL, although this may not be necessary, it is good for me to learn these principles. My question is: With these priorities, would I have any benefit by choosing either Linq2Sql vs. EntityFramwork? (and please explain why) Btw, the project involves very simple table scheme with only 4-5 tables and very simple relations. Thanks!

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Why is this CHOICE element not getting assigned in my SharePoint Field definition schema?

- by ccornet

I defined a new field of the type "Choice" for my web application. It will serve basically as a pseudo-lookup as its contents are defined by the value of a Text field in a list. It is initialized with a dummy choice to begin with (I'm under the impression a choice field needs at least one choice when defined), which is replaced with a real choice later on. But for some reason, this dummy choice is never actually added to the choices! Below is the XML Schema for the field in question. <Field ID="{ALICEH-ASFA-KEGU-IDLISTED}" Name="ddlSystems" Group="Lookup Columns" DisplayName="ddlSystems" Type="Choice" Sealed="FALSE" ReadOnly="FALSE" Hidden="FALSE" FillInChoice="TRUE" DisplaceOnUpgrade="TRUE"> <CHOICES> <CHOICE>BLANULL</CHOICE> </CHOICES> <Default>BLANULL</Default> </Field> Initially, I used a default choice of (a single space), but I changed it to BLANULL so that I can parse an actual word instead of a veritably empty string. Now, even after having uninstalled and reinstalled the feature with this field, I have a choice field that has (still a single space) as the only choice. Even more perplexing, BLANULL is actually listed for the default value in both the UI and the object model! What is causing this problem, and how can I circumvent it so that I don't have to manually set this dummy value each time?

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How to sort an XML file by date in XLST

- by AdRock

I am trying to sort by date and get an error message about the stylesheet can't be loaded I found an answer on how others have suggested but it doesn't work for me Here is where it is supposed to sort. The commented out line is where the sort should occur <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:template name="hoo" match="/"> <html> <head> <title>Registered Festival Organisers and Festivals</title> <link rel="stylesheet" type="text/css" href="userfestival.css" /> </head> <body> <h1>Registered Festival Organisers and Festivals</h1> <xsl:for-each select="folktask/member"> <xsl:if test="user/account/userlevel='3'">  Sample node from XML <festival id="1"> <event> <eventname>Oxford Folk Festival</eventname> <url>http://www.oxfordfolkfestival.com/</url> <datefrom>2010-04-07</datefrom> <dateto>2010-04-09</dateto> <location>Oxford</location> <eventpostcode>OX1 9BE</eventpostcode> <coords> <lat>51.735640</lat> <lng>-1.276136</lng> </coords> </event> </festival>

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lambda traits inconsistency across C++0x compilers

- by Sumant

I observed some inconsistency between two compilers (g++ 4.5, VS2010 RC) in the way they match lambdas with partial specializations of class templates. I was trying to implement something like boost::function_types for lambdas to extract type traits. Check this for more details. In g++ 4.5, the type of the operator() of a lambda appears to be like that of a free standing function (R (*)(...)) whereas in VS2010 RC, it appears to be like that of a member function (R (C::*)(...)). So the question is are compiler writers free to interpret any way they want? If not, which compiler is correct? See the details below. template <typename T> struct function_traits : function_traits<decltype(&T::operator())> { // This generic template is instantiated on both the compilers as expected. }; template <typename R, typename C> struct function_traits<R (C::*)() const> { // inherits from this one on VS2010 RC typedef R result_type; }; template <typename R> struct function_traits<R (*)()> { // // inherits from this one g++ 4.5 typedef R result_type; }; int main(void) { auto lambda = []{}; function_traits<decltype(lambda)>::result_type *r; // void * } This program compiles on both g++ 4.5 and VS2010 but the function_traits that are instantiated are different as noted in the code.

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gcc, strict-aliasing, and horror stories

- by Joseph Quinsey

In http://stackoverflow.com/questions/2906365/gcc-strict-aliasing-and-casting-through-a-union I asked whether anyone had encountered problems with union punning through pointers. So far, the answer seems to be No. This question is broader: do you have any horror stories about gcc and strict-aliasing? Background: Quoting from AndreyT's answer in http://stackoverflow.com/questions/2771023/c99-strict-aliasing-rules-in-c-gcc/2771041#2771041: "Strict aliasing rules are rooted in parts of the standard that were present in C and C++ since the beginning of [standardized] times. The clause that prohibits accessing object of one type through a lvalue of another type is present in C89/90 (6.3) as well as in C++98 (3.10/15). ... It is just that not all compilers wanted (or dared) to enforce it or rely on it." Well, gcc is now daring to do so, with its -fstrict-aliasing switch. And this has caused some problems. See, for example, the excellent article http://davmac.wordpress.com/2009/10/ about a Mysql bug, and the equally excellent discussion in http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html. Some other less-relevant links: http://stackoverflow.com/questions/1225741/performance-impact-of-fno-strict-aliasing http://stackoverflow.com/questions/754929/strict-aliasing http://stackoverflow.com/questions/262379/when-is-char-safe-for-strict-pointer-aliasing http://stackoverflow.com/questions/725138/how-to-detect-strict-aliasing-at-compile-time So to repeat, do you have a horror story of your own? Problems not indicated by -Wstrict-aliasing would, of course, be preferred. And other C compilers are also welcome.

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CSS background images not showing in IE?

- by Kevin

In IE8 and below, I'm doing this <ul class="dependants_list" style="border-bottom: dashed 1px #53a1dc"> <li class="dependants_summary"> <strong>Name:</strong> De Silva, Angelina<br /> <strong>Gender:</strong> Female<br /> <strong>Date of birth:</strong> 7/3/2009<br /> </li> <form action="/Dependant/Delete/11413" method="get"><input class="delete btn" id="Delete_this_Profile" name="Delete_this_Profile" type="submit" value="Delete this Profile" /> </form><form action="/Dependant/Edit/11413" method="get"><input class="edit btn" id="Modify_this_Profile" name="Modify_this_Profile" type="submit" value="Modify this Profile" /> </form><br /><hr style="display:none" /> and the CSS for it is: .dependants_summary { overflow: hidden; margin-bottom: 10px; padding-right: 0px; padding-left: 85px; padding-top: 5px; padding-bottom: 5px; width: 430px; float: left; font: 120% Arial, Helvetica, sans-serif; } .dependants_list { padding: 0; } .dependants_list li:nth-child(odd) { background: #fff url("../images/dependant_male.png") no-repeat scroll 8px 9px; } .dependants_list li:nth-child(even) { background: #c9e3f4 url("../images/dependant_male.png") no-repeat scroll 8px 9px; } The images are not being shown in IE, but they are in ffox and chrome

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Passing parameters in MVC

- by Avinash

Thare is two forms in a page first one for searching and another for deleting.... <table><tr><td> <% using(Html.BeginForm("ViewList","ControllerName", [values],FormMethod.Post,new{id="viewListForm"})) { %> Name: <%=Html.TextBox("Name", "[value]", new { maxlength = "250" })%> Location: <%=Html.TextBox("Location", "[Value]", new { maxlength = "250" })%> <input type="submit" id="Search" name="Search" value="Search" /> <% } %> </td></tr> <tr><td> <% using(Html.BeginForm("DeleteList","ControllerName", new { name=?,location=? },[values],FormMethod.Post, new{id="deleteListForm"})) { %> [here the code for all items displayed in a table.] <input type="submit" id="Delete" name="Delete" value="Delete" /> When delete buttom pressed i need to pass two parameters ie name and location. The values of name and location are in the above viewListForm. How i take this value from the viewListForm at run time ? <% } %> </td></tr><table>

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Float addition promoted to double?

- by Andreas Brinck

I had a small WTF moment this morning. Ths WTF can be summarized with this: float x = 0.2f; float y = 0.1f; float z = x + y; assert(z == x + y); //This assert is triggered! (Atleast with visual studio 2008) The reason seems to be that the expression x + y is promoted to double and compared with the truncated version in z. (If i change z to double the assert isn't triggered). I can see that for precision reasons it would make sense to perform all floating point arithmetics in double precision before converting the result to single precision. I found the following paragraph in the standard (which I guess I sort of already knew, but not in this context): 4.6.1. "An rvalue of type float can be converted to an rvalue of type double. The value is unchanged" My question is, is x + y guaranteed to be promoted to double or is at the compiler's discretion? UPDATE: Since many people has claimed that one shouldn't use == for floating point, I just wanted to state that in the specific case I'm working with, an exact comparison is justified. Floating point comparision is tricky, here's an interesting link on the subject which I think hasn't been mentioned.

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How do I set a flash object to open a url in a new window?

- by Keith Donegan

Hi Guys, I have this code: <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,28,0" width="300" height="250"> <param name="movie" value="Spotify_premium_300x250.swf" /> <param name="quality" value="high" /> <embed src="Spotify_premium_300x250.swf" quality="high" pluginspage="http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash" type="application/x-shockwave-flash" width="300" height="250"></embed> </object> EDIT: Code from Tom <object onclick="javascript: window.open('http://www.stackoverflow.com', _blank, 'width=1024, height=600, menubar=no, resizable=yes');" classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,28,0" width="300" height="250"> <param name="movie" value="Spotify_premium_300x250.swf" /> <param name="quality" value="high" /> <embed src="Spotify_premium_300x250.swf" quality="high" pluginspage="http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash" type="application/x-shockwave-flash" width="300" height="250"></embed> </object> I would like it as when a user clicks the flash object, it's opens a URL in a new window. How would I go about doing this? Cheers, Keith

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ASP.NET catching controls from html generated from the database

- by Drahcir

I have a set of websites that basically do the exact same thing in terms of functionality, the only thing that varies is the css and how the html is laid out. Is there a way to generate the html from a database (ie retreiving the html from a table) and then catching the controls (like buttons, textboxes etc) from the code behind? UPDATE: Here is an example of what I want to acheive: <html> <div id="generatedContent" runat="server">  <div> This is a textbox <input id="tb1" runat="server" type="text" /> This is a button <input type="submit" id="btn1" runat="server" value="My Button" /> </div> </div> </html> This is the code behind var tb1 = new HtmlControls.HtmlInputText(); tb1 = FindControl("tb1"); var btn1 = new New HtmlControls.HtmlInputSubmit(); btn1 = FindControl("btn1"); Now obviously since the html has been generated from the database (ie after the page has already been initialised) the FindControl method will return null.

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MVC2 DataAnnotations on ViewModel - Don't understand using it with MVVM pattern

- by ScottSEA

I have an MVC2 Application that uses MVVM pattern. I am trying use Data Annotations to validate form input. In my ThingsController I have two methods: [HttpGet] public ActionResult Index() { return View(); } public ActionResult Details(ThingsViewModel tvm) { if (!ModelState.IsValid) return View(tvm); try { Query q = new Query(tvm.Query); ThingRepository repository = new ThingRepository(q); tvm.Things = repository.All(); return View(tvm); } catch (Exception) { return View(); } } My Details.aspx view is strongly typed to the ThingsViewModel: <%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<Config.Web.Models.ThingsViewModel>" %> The ViewModel is a class consisting of a IList of returned Thing objects and the Query string (which is submitted on the form) and has the Required data annotation: public class ThingsViewModel { public IList<Thing> Things{ get; set; } [Required(ErrorMessage="You must enter a query")] public string Query { get; set; } } When I run this, and click the submit button on the form without entering a value I get a YSOD with the following error: The model item passed into the dictionary is of type 'Config.Web.Models.ThingsViewModel', but this dictionary requires a model item of type System.Collections.Generic.IEnumerable`1[Config.Domain.Entities.Thing]'. How can I get Data Annotations to work with a ViewModel? I cannot see what I'm missing or where I'm going wrong - the VM was working just fine before I started mucking around with validation.

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PHP image watermark only displaying image on page

- by Satch3000

I am testing a script where I watermark an image in my webpage. The script works fine and the image is watermark but my problem is that only the image is displayed on the page. As soon as I add the script to my page it's like the web page is converted to the image that I'm watermarking. I think it's because of header("content-type: image/jpeg"); from the code. I need to watermark the image on my webpage but I also need the rest of my webpage to be displayed too. How is this done? I'm quite confused on how this works. The script I'm using is from here Here's the code I'm using: <?php $main_img = "Porsche_911_996_Carrera_4S.jpg"; // main big photo / picture $watermark_img = "watermark.gif"; // use GIF or PNG, JPEG has no tranparency support $padding = 3; // distance to border in pixels for watermark image $opacity = 100; // image opacity for transparent watermark $watermark = imagecreatefromgif($watermark_img); // create watermark $image = imagecreatefromjpeg($main_img); // create main graphic if(!$image || !$watermark) die("Error: main image or watermark could not be loaded!"); $watermark_size = getimagesize($watermark_img); $watermark_width = $watermark_size[0]; $watermark_height = $watermark_size[1]; $image_size = getimagesize($main_img); $dest_x = $image_size[0] - $watermark_width - $padding; $dest_y = $image_size[1] - $watermark_height - $padding; // copy watermark on main image imagecopymerge($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, $opacity); // print image to screen header("content-type: image/jpeg"); imagejpeg($image); imagedestroy($image); imagedestroy($watermark); ?> NOTE: I'm getting the image path from the database so I cannot hardcode the image filename as it's dynamic.

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Display pdf file inline in Rails app

- by Martas

Hi, I have a pdf file attachment saved in the cloud. The file is attached using attachment_fu. All I do to display it in the view is: <%= image_tag @model.pdf_attachment.public_filename %> When I load the page with this code in the browser, it does what I want: it displays the attached pdf file. But only on Mac. On Windows, browsers will display a broken image placeholder. Chrome's Developer Tools report: "Resource interpreted as image but transferred with MIME type application/pdf." I also tried sending the file from controller: in PdfAttachmentController: def send_pdf_attachment pdf_attachment = PdfAttachment.find params[:id] send_file pdf_attachment.public_filename, :type => pdf_attachment.content_type, :file_name => pdf_attachment.filename, :disposition => 'inline' end in routes.rb: map.send_pdf_attachment '/pdf_attachments/send_pdf_attachment/:id', :controller => 'pdf_attachments', :action => 'send_pdf_attachment' and in the view: <%= send_pdf_attachment_path @model.pdf_attachment %> or <%= image_tag( send_pdf_attachment_path @model.pdf_attachment ) %> And that doesn't display the file on Mac (I didn't try on Windows), it displays the path: pdf_attachments/send_pdf_attachment/35 So, my question is: what do I do to properly display a pdf file inline? Thanks martin

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Collision detections and how efficient they are

- by Shadow

How exactly do you implement collision detection? What are the costs involved? Do different platforms(c/c++, java, cocoa/iphone, flash, directX) have different optimizations for calculating collisions. And lastly are there libraries available to do this for me, or some that I can just interpret for my platform of choice? As I understand it you would need to loop through the collision map and find the area in question and then compair the input thing(e.g. a sprite) to the type of pixel that is in the questioned area. I understand the very basic idea, but I don't understand the underlying implementation or even a higher level one for that matter. It would seem that this type of detection, or any for that matter, is very costly. Tile map? Bit array? How are these created from an image(I would guess looping and doing stuff)? The reason I ask this question is to get a better understanding of the efficiency behind the scenes and to understand exactly what is going on. Links, references, or examples would be very helpful. I know this question is a bit longwinded so any help or references would be very welcome. Thanks SO!

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curios about CCSpriteBatchNode's addchild method

- by lzyy

when diving into "learn cocos2d game development with ios5", in ch08 in EnemyCache.m -(id) init { if ((self = [super init])) { // get any image from the Texture Atlas we're using CCSpriteFrame* frame = [[CCSpriteFrameCache sharedSpriteFrameCache] spriteFrameByName:@"monster-a.png"]; batch = [CCSpriteBatchNode batchNodeWithTexture:frame.texture]; [self addChild:batch]; [self initEnemies]; [self scheduleUpdate]; } return self; } so batch is with texture "monster-a.png" in EnemyEntity.m's initWithType method switch (type) { case EnemyTypeUFO: enemyFrameName = @"monster-a.png"; bulletFrameName = @"shot-a.png"; break; case EnemyTypeCruiser: enemyFrameName = @"monster-b.png"; bulletFrameName = @"shot-b.png"; shootFrequency = 1.0f; initialHitPoints = 3; break; case EnemyTypeBoss: enemyFrameName = @"monster-c.png"; bulletFrameName = @"shot-c.png"; shootFrequency = 2.0f; initialHitPoints = 15; break; default: [NSException exceptionWithName:@"EnemyEntity Exception" reason:@"unhandled enemy type" userInfo:nil]; } if ((self = [super initWithSpriteFrameName:enemyFrameName])) { //... } so the returned object may be in 3 different frame. since Only the CCSprites that are contained in that texture can be added to the CCSpriteBatchNode, obviously, 'monster-b.png' is not contained in 'monster-a.png', why the different enemy can still be added to the batch?

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No output got after execution.

- by wilson88

I am still stuck with getting output for a copied vector. Probably something am not doing right. I get no output. void Auctioneer::accept_bids(const BidList& bid){ BidList list; BidList list2; BidList::const_iterator iter; copy (list.begin(),list.end(), back_inserter(list2)); for(iter=list2.begin(); iter != list2.end(); iter++) { const Bid& bid = *iter; // Get a reference to the Bid object that the iterator points to cout << "Bid id : " << bid.bidId << endl; cout << "Trd id : " << bid.trdId << endl; cout << "Quantity: " << bid.qty << endl; cout << "Price : " << bid.price << endl; cout << "Type : " << bid.type << endl; } }

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Is this a safe/valid hash method implementation?

- by Sean

I have a set of classes to represent some objects loaded from a database. There are a couple variations of these objects, so I have a common base class and two subclasses to represent the differences. One of the key fields they have in common is an id field. Unfortunately, the id of an object is not unique across all variations, but within a single variation. What I mean is, a single object of type A could have an id between, say, 0 and 1,000,000. An object of type B could have an id between, 25,000 and 1,025,000. This means there's some overlap of id numbers. The objects are just variations of the same kind of thing, though, so I want to think of them as such in my code. (They were assigned ids from different sets for legacy reasons.) So I have classes like this: @class BaseClass @class TypeAClass : BaseClass @class TypeBClass : BaseClass BaseClass has a method (NSNumber *)objectId. However instances of TypeA and TypeB could have overlapping ids as discussed above, so when it comes to equality and putting these into sets, I cannot just use the id alone to check it. The unique key of these instances is, essentially, (class + objectId). So I figured that I could do this by making the following hash function on the BaseClass: -(NSUInteger)hash { return (NSUInteger)[self class] ^ [self.objectId hash]; } I also implemented isEqual like so: - (BOOL)isEqual:(id)object { return (self == object) || ([object class] == [self class] && [self.objectId isEqual:[object objectId]]); } This seems to be working, but I guess I'm just asking here to make sure I'm not overlooking something - especially with the generation of the hash by using the class pointer in that way. Is this safe or is there a better way to do this?

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Returning the element number of the longest string in an array

- by JohnRoberts

I'm trying to get the longestS method to take the user-inputted array of strings, then return the element number of the longest string in that array. I got it to the point where I was able to return the number of chars in the longest string, but I don't believe that will work for what I need. My problem is that I keep getting incompatible type errors when trying to figure this out. I don't understand the whole data type thing with strings yet. It's confusing me how I go about return a number of the array yet the array is of strings. The main method is fine, I got stuck on the ???? part. { public static void main(String [] args) { Scanner inp = new Scanner( System.in ); String [] responseArr= new String[4]; for (int i=0; i<4; i++) { System.out.println("Enter string "+(i+1)); responseArr[i] = inp.nextLine(); } int highest=longestS(responseArr); } public static int longestS(String[] values) { int largest=0 for( int i = 1; i < values.length; i++ ) { if ( ????? ) } return largest; } }

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Are there pitfalls to using static class/event as an application message bus

- by Doug Clutter

I have a static generic class that helps me move events around with very little overhead: public static class MessageBus<T> where T : EventArgs { public static event EventHandler<T> MessageReceived; public static void SendMessage(object sender, T message) { if (MessageReceived != null) MessageReceived(sender, message); } } To create a system-wide message bus, I simply need to define an EventArgs class to pass around any arbitrary bits of information: class MyEventArgs : EventArgs { public string Message { get; set; } } Anywhere I'm interested in this event, I just wire up a handler: MessageBus<MyEventArgs>.MessageReceived += (s,e) => DoSomething(); Likewise, triggering the event is just as easy: MessageBus<MyEventArgs>.SendMessage(this, new MyEventArgs() {Message="hi mom"}); Using MessageBus and a custom EventArgs class lets me have an application wide message sink for a specific type of message. This comes in handy when you have several forms that, for example, display customer information and maybe a couple forms that update that information. None of the forms know about each other and none of them need to be wired to a static "super class". I have a couple questions: fxCop complains about using static methods with generics, but this is exactly what I'm after here. I want there to be exactly one MessageBus for each type of message handled. Using a static with a generic saves me from writing all the code that would maintain the list of MessageBus objects. Are the listening objects being kept "alive" via the MessageReceived event? For instance, perhaps I have this code in a Form.Load event: MessageBus<CustomerChangedEventArgs>.MessageReceived += (s,e) => DoReload(); When the Form is Closed, is the Form being retained in memory because MessageReceived has a reference to its DoReload method? Should I be removing the reference when the form closes: MessageBus<CustomerChangedEventArgs>.MessageReceived -= (s,e) => DoReload();

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Case class copy() method abstraction.

- by Joa Ebert

I would like to know if it is possible to abstract the copy method of case classes. Basically I have something like sealed trait Op and then something like case class Push(value: Int) extends Op and case class Pop() extends Op. The first problem: A case class without arguments/members does not define a copy method. You can try this in the REPL. scala> case class Foo() defined class Foo scala> Foo().copy() <console>:8: error: value copy is not a member of Foo Foo().copy() ^ scala> case class Foo(x: Int) defined class Foo scala> Foo(0).copy() res1: Foo = Foo(0) Is there a reason why the compiler makes this exception? I think it is rather unituitive and I would expect every case class to define a copy method. The second problem: I have a method def ops: List[Op] and I would like to copy all ops like ops map { _.copy() }. How would I define the copy method in the Op trait? I get a "too many arguments" error if I say def copy(): this.type. However, since all copy() methods have only optional arguments: why is this incorrect? And, how do I do that correct? By making another method named def clone(): this.type and write everywhere def clone() = copy() for all the case classes? I hope not.

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xsd.exe creating invalid constraints in dataset from xsd file

- by Dan Neely

I have a sequence with an allowed minimum length of zero in my xsd. When I try and load an xml file which doesn't have any elements of the sequence into the DataSet that xsd.exe created I get an exception indicating that my file violated one of the DataSet's constraints. The xml file validates against the schema so I know it's valid. Is there anything I can do to make the tool generate a valid dataset? <xs:sequence minOccurs="0" maxOccurs="unbounded"> <xs:element name="Numbers" type="xs:double"/> </xs:sequence> Edit: if I change my schema to this the generated code works properly. It looks wrong to me though since it appears to be implying that I could have sequence items with nothing in them, which doesn't make any sense. <xs:sequence minOccurs="0" maxOccurs="unbounded"> <xs:element name="Numbers" type="xs:double" minOccurs="0"/> </xs:sequence>

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