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  • Legitimate uses of the Function constructor

    - by Marcel Korpel
    As repeatedly said, it is considered bad practice to use the Function constructor (also see the ECMAScript Language Specification, 5th edition, § 15.3.2.1): new Function ([arg1[, arg2[, … argN]],] functionBody) (where all arguments are strings containing argument names and the last (or only) string contains the function body). To recapitulate, it is said to be slow, as explained by the Opera team: Each time […] the Function constructor is called on a string representing source code, the script engine must start the machinery that converts the source code to executable code. This is usually expensive for performance – easily a hundred times more expensive than a simple function call, for example. (Mark ‘Tarquin’ Wilton-Jones) Though it's not that bad, according to this post on MDC (I didn't test this myself using the current version of Firefox, though). Crockford adds that [t]he quoting conventions of the language make it very difficult to correctly express a function body as a string. In the string form, early error checking cannot be done. […] And it is wasteful of memory because each function requires its own independent implementation. Another difference is that a function defined by a Function constructor does not inherit any scope other than the global scope (which all functions inherit). (MDC) Apart from this, you have to be attentive to avoid injection of malicious code, when you create a new Function using dynamic contents. Lots of disadvantages and it is intelligible that ECMAScript 5 discourages the use of the Function constructor by throwing an exception when using it in strict mode (§ 13.1). That said, T.J. Crowder says in an answer that [t]here's almost never any need for the similar […] new Function(...), either, again except for some advanced edge cases. So, now I am wondering: what are these “advanced edge cases”? Are there legitimate uses of the Function constructor?

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  • Wicket Drag and drop functionality for adding an image

    - by Marcel
    I'm making a wicket app that can manage some options for a cashdesk app. One of the options is to change the image of a selected Product. The user(manager) can choose from the already present images in the database (SQL) when this option is selected, or add a new image if the desired image is not present. Don't mention the test names and awesome images (it's still in test-fase) I prefer to see the adding of an image achieved by Drag and Drop html5 demo [dnd-upload] (From the desktop into the browser) I'm currently using Wicket-6.2.0 and wicket-dnd 0.5.0 and i can't seem to get this working! All examples I can find are from wicket 2.x or lower. It is possible to use drag and drop in Wicket-6.2, but how do I achieve this? There seems to be some DraggableBehavior in wicket? Any help is welcome! [UPDATE] Upgraded to wicket-dnd 0.6

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  • What is the difference between "LINQ to Entities", "LINQ to SQL" and "LINQ to Dataset".

    - by Marcel
    I've been working for quite a while now with LINQ. However, it remains a bit of a mystery what the real differences are between the mentioned flavours of LINQ. The successful answer will contain a short differentiation between them. What is the main goal of each flavor, what is the benefit, and is there a performance impact... P.S. I know that there are a lot of information sources out there, but I'm looking for a kind of a "cheat sheet" which instructs a newbie where to head for a specific goal.

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  • What is the differnce between "LINQ to Entities", "LINQ to SQL" and "LINQ to Dataset".

    - by Marcel
    Hi all, I'm working for quite a while now with LINQ. However, it remained still a bit of a mystery what are the real differences between the mentioned flavours of LINQ. The successful answer will contain a short differentiation between them. What is the main goal if it, what is the benefit, and is there a performance impact... P.S. I know that there are a lot of information sources out there, but I look for a kind of a "cheat sheet" which instructs a newbie where to head to for a specific goal.

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  • How to execute a perl script within php and capture error messages?

    - by Marcel Tjandraatmadja
    I am trying to execute a Perl script like so: /usr/bin/ec2-consistent-snapshot 'vol-dr3131c2' When the Perl script fails it exits using 'die' and prints out an error message. I can see that error message when executing manually, but I am failing to capture it through PHP. I tried the following with no success: exec($command,$output); echo system($command,$output); passthru($command); Any ideas?

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  • Why does my Eclipse crash all the time?

    - by Marcel
    Somehow stupid question, I have to admit - hope it won't cost me too many points. To make it clear: I would also be happy if you can help me find the reason for the crashes. I wouldn't expect a precise answer. However, I don't see why my Eclipse is crashing (freezing) all the time. Mostly when I save a file. For some reason, crashes seem to increase lately... I use Eclipse Helios (Version: 3.6.1) and java version "1.6.0_20" (OpenJDK Runtime Environment (IcedTea6 1.9.2) (6b20-1.9.2-0ubuntu2) OpenJDK 64-Bit Server VM (build 19.0-b09, mixed mode)) on Ubuntu 10.10 (64-Bit). Thank you!

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  • LINQ: How to skip one then take the rest of a sequence

    - by Marcel
    Hi All, i would like to iterate over the items of a List<T>, except the first, preserving the order. Is there an elegant way to do it with LINQ using a statement like: foreach (var item in list.Skip(1).TakeTheRest()) {.... I played around with TakeWhile , but was not successful. Probably there is also another, simple way of doing it?

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  • In C#: How to declare a generic Dictionary with a type as key and an enumeration of that type as val

    - by Marcel
    Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: (Edited to follow johny g's comment) private IDictionary<Type, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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  • UIButton performance in UITableViewCell vs UIView

    - by marcel salathe
    I'd like to add a UIButton to a custom UITableViewCell (programmatically). This is easy to do, but I'm finding that the "performance" of the button in the cell is slow - that is, when I touch the button, there is quite a bit of delay until the button visually goes into the highlighted state. The same type of button on a regular UIView is very responsive in comparison. In order to isolate the problem, I've created two views - one is a simple UIView, the other is a UITableView with only one UITableViewCell. I've added buttons to both views (the UIView and the UITableViewCell), and the performance difference is quite striking. I've searched the web and read the Apple docs but haven't really found the cause of the problem. My guess is that it somehow has to do with the responder chain, but I can't quite put my finger on it. I must be doing something wrong, and I'd appreciate any help. Thanks. Demo code: ViewController.h #import <UIKit/UIKit.h> @interface ViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> @property UITableView* myTableView; @property UIView* myView; ViewController.m #import "ViewController.h" #import "CustomCell.h" @implementation ViewController @synthesize myTableView, myView; - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { [self initMyView]; [self initMyTableView]; } return self; } - (void) initMyView { UIView* newView = [[UIView alloc] initWithFrame:CGRectMake(0,0,[[UIScreen mainScreen] bounds].size.width,100)]; self.myView = newView; // button on regularView UIButton* myButton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; [myButton addTarget:self action:@selector(pressedMyButton) forControlEvents:UIControlEventTouchUpInside]; [myButton setTitle:@"I'm fast" forState:UIControlStateNormal]; [myButton setFrame:CGRectMake(20.0, 10.0, 160.0, 30.0)]; [[self myView] addSubview:myButton]; } - (void) initMyTableView { UITableView *newTableView = [[UITableView alloc] initWithFrame:CGRectMake(0,100,[[UIScreen mainScreen] bounds].size.width,[[UIScreen mainScreen] bounds].size.height-100) style:UITableViewStyleGrouped]; self.myTableView = newTableView; self.myTableView.delegate = self; self.myTableView.dataSource = self; } -(void) pressedMyButton { NSLog(@"pressedMyButton"); } - (void)viewDidLoad { [super viewDidLoad]; [[self view] addSubview:self.myView]; [[self view] addSubview:self.myTableView]; } - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 1; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return 1; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { CustomCell *customCell = [tableView dequeueReusableCellWithIdentifier:@"CustomCell"]; if (customCell == nil) { customCell = [[CustomCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"CustomCell"]; } return customCell; } @end CustomCell.h #import <UIKit/UIKit.h> @interface CustomCell : UITableViewCell @property (retain, nonatomic) UIButton* cellButton; @end CustomCell.m #import "CustomCell.h" @implementation CustomCell @synthesize cellButton; - (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier { self = [super initWithStyle:style reuseIdentifier:reuseIdentifier]; if (self) { // button within cell cellButton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; [cellButton addTarget:self action:@selector(pressedCellButton) forControlEvents:UIControlEventTouchUpInside]; [cellButton setTitle:@"I'm sluggish" forState:UIControlStateNormal]; [cellButton setFrame:CGRectMake(20.0, 10.0, 160.0, 30.0)]; [self addSubview:cellButton]; } return self; } - (void) pressedCellButton { NSLog(@"pressedCellButton"); } @end

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  • A good way to implement useable Callbacks in C++

    - by Marcel J.
    I have a custom Menu class written in C++. To seperate the code into easy-to-read functions I am using Callbacks. Since I don't want to use Singletons for the Host of the Menu I provide another parameter (target) which will be given to the callback as the first parameter (some kind of workaround for the missing "this" reference). Registration-Signature AddItem(string s, void(*callback)(void*,MenuItem*), void* target = NULL) Example of a Registration menu->AddItem(TRANSLATE, "translate", &MyApp::OnModeSelected); Example of a Handler /* static */ void MyApp::OnModeSelected(void* that, MenuItem* item) { MyApp *self = (MyApp*)that; self->activeMode = item->text; } Is there anything one could consider dirty with this approach? Are there maybe better ones?

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  • Missing Status Bar in Visual Studio?

    - by Marcel
    Note: This question and answer is a full copy from Kelly Brownsbergers Blog. I do post it as a convenience to others. From time to time, my status bar disappears. I used to believe this was due to a botched install or add-in. I recently upgraded to Team System Test Edition, and my status bar again disappeared. For the last few weeks I’ve been trying to figure out a time to do a full reinstall. To not take rep for this, I have marked it communitiy wiki.

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  • In C#: How to declare a generic Dictionary whose key and value types have a common constraint type?

    - by Marcel
    Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: private IDictionary<T, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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  • Selecting text between Brackets in an input field with Jquery

    - by Marcel
    Hi, with $("#TextInputElement").select() I am able to select a text (mark it) in an in an input text field. Now I only want to select the text in between brackets in that input field. I have the regular expression match(/-[^-]*-/) to select, but how would I apply this to only select the text inside the input field between brackets? [noselect]textToBeSelected[/noselect] thx

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  • Focus on input field with value

    - by Marcel
    Hi, i am focusing on an input field with jquerys $("input:text").focus(); There is allready some textvalue in the inputfield. When I focus, the cursor blinks right after the last letter, how would I put the cursor right in front of the first letter? thx alot

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  • Reversing a number in c++

    - by Marcel Bujnowski
    I created a program to show the sum and show the reversed number a person has typed. The sum function works but the revers function is not. Can anyone give me any tips on how to fix it. I created a program to show the sum and show the reversed number a person has typed. The sum function works but the revers function is not. Can anyone give me any tips on how to fix it. #include<iostream> #include<iomanip> using namespace std; void printSum(int n, bool reverse); int sm(int n); int reverseInt(int n); void printAddTable(int n); int main() { int reverse; int sum=0; int n; cout<<"Enter N value:"<<endl; cin>>n; if(n>0) { reverse = true; printSum( n, reverse); // calls the printSum Method } else { //cout<<"enter positive Number only:"<<endl; } sum = sm(n); //err // calls the sum Method reverse = reverseInt(n); // calls the reverseInt Method cout<<"The reverse value is:"<<reverse; printAddTable(n); // calls the printAddTable Method //getch() } //end of main() void printSum(int n, bool reverse) { int sum=0; // print sum of reverse numbers for(int i=n; i>=1; i--) { sum=sum+i; cout<<i<< " "<<"+"<<" "; } cout<<sum; } int sm(int n) {int sum =0; for(int i=1; i<=n; i++) { sum = sum + i ; cout << endl; cout<<i<<" "<<"+"<<" "<<endl; // print n positive integers cout << endl; } cout<< "Are " <<n<< " positive integers"<<endl; cout<< "Sum is "<<sum <<endl; return sum; } int reverseInt(int n) { int reminder=0; int sum =0; while(n<=0) { reminder = n/10; sum = (sum * 10) + reminder; // it returns the reverse number n = n % 10; } return sum; } void printAddTable(int n) { for(int i=1; i<=n; i++) { cout<<i<<endl; for(int j=1; j<=n; j++) // print n X n add table { cout<<i+j<<endl; } } } {

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