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• What advantage does Monad give us over an Applicative?

  - by arrowdodger

  I've read this article, but didn't understand last section. The author says that Monad gives us context sensitivity, but it's possible to achieve the same result using only an Applicative instance: let maybeAge = (\futureYear birthYear -> if futureYear < birthYear then yearDiff birthYear futureYear else yearDiff futureYear birthYear) <$> (readMay futureYearString) <*> (readMay birthYearString) It's uglier for sure, but beside that I don't see why we need Monad. Can anyone clear this up for me?

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• The glutKeyboardFunc does not react to key presses immediately

  - by Nibirue

  I have a function glutKeyboardFunc(keyboard), where keyboard has: void keyboard(unsigned char key, int x, int y){ float alpha = 1.0; switch(key){ case 'c': glClearColor(1,0,0,alpha); printf("success"); break; } } This is a summary of the function; it works properly, but only once some other action has occurred. For instance, the printf statement reports success immediately on keystroke 'c', but the background color does not become active until I click somewhere else on the canvas. I want all keystrokes to have an immediate effect.

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• What is the logic behind defining macros inside a struct?

  - by systemsfault

  As apparent in the title, I'm questioning the reason behind defining the macros inside a struct. I frequently see this approach in network programming for instance following snippet: struct sniff_tcp { u_short th_sport; /* source port */ u_short th_dport; /* destination port */ tcp_seq th_seq; /* sequence number */ tcp_seq th_ack; /* acknowledgement number */ u_char th_offx2; /* data offset, rsvd */ #define TH_OFF(th) (((th)->th_offx2 & 0xf0) >> 4) u_char th_flags; #define TH_FIN 0x01 #define TH_SYN 0x02 #define TH_RST 0x04 #define TH_PUSH 0x08 #define TH_ACK 0x10 #define TH_URG 0x20 #define TH_ECE 0x40 #define TH_CWR 0x80 #define TH_FLAGS (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR) u_short th_win; /* window */ u_short th_sum; /* checksum */ u_short th_urp; /* urgent pointer */ }; This example is from sniffex.c code in tcpdump's web site. Is this for enhancing readability and making code clearer.

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• Quickest way to clone a GregorianCalendar?

  - by wds

  I'm trying to make a deep copy of an object, including a GregorianCalendar instance. I'm always wary of using clone() and it doesn't seem to have been overridden here, so I'm just doing the copy field by field. Ideally, there'd be a copy constructor, which I could use like so: GregorianCalendar newCalendar = new GregorianCalendar(oldCalendar); Unfortunately I can't find any such functionality in the API and am stuck trying to figure out which fields I need to get an exact copy. So, to make a copy of one of these calendars, how would you do it? Am I missing some simple shortcut here?

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• Use LINQ to insert data from dataset to SQL

  - by Mayo

  Let's say I have a dataset in an ASP.NET website (.NET 3.5) with 5 tables, each has roughly 30,000 rows and an average of 12 columns. I want to insert all of the data from the dataset into 5 very-similar-but-not-quite-identical tables in SQL Server 2008. I also want to use LINQ (personal preference - trying to learn something new). Is it as simple as iterating through the dataset and, for each row, creating a new instance of the associated class, initializing its data with the dataset's row, adding it to the data model, and then doing one giant SubmitChanges at the end? Are there better ways of doing this with LINQ? Or is this the de-facto standard?

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• How does lock(syncRoot) make sense on a static method?

  - by Rising Star

  The following code is excerpted from the (Windows Identity Foundation SDK) template that MS uses to create a new Security Token Service Web Site. public static CustomSecurityTokenServiceConfiguration Current { get { HttpApplicationState httpAppState = HttpContext.Current.Application; CustomSecurityTokenServiceConfiguration customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { lock ( syncRoot ) { customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { customConfiguration = new CustomSecurityTokenServiceConfiguration(); httpAppState.Add( CustomSecurityTokenServiceConfigurationKey, customConfiguration ); } } } return customConfiguration; } } I'm relatively new to multi-threaded programming. I assume that the reason for the lock statement is to make this code thread-safe in the event that two web requests arrive at the web site at the same time. However, I would have thought that using lock (syncRoot) would not make sense because syncRoot refers to the current instance that this method is operating on... but this is a static method? How does this make sense?

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• What exactly does a self-describing type in .Net mean?

  - by tzup

  Given this MSDN article, we learn that the Common Type System in .Net has this classification of reference types: "Reference types can be self-describing types, pointer types, or interface types. The type of a reference type can be determined from values of self-describing types. Self-describing types are further split into arrays and class types." So an array, for instance, is a self-describing type because we can determine it's type from its values? How? Is that it, or is there more to this definition?

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• How do a search a table for similar records and displaying count - Ruby on Rails

  - by bgadoci

  I have created a table in my Ruby on Rails application that I am building called Tags. It is a blog application so I allow the user to associate tags with a post and do this through a :posts, :has_many = tags and Tag belongs_to :post association. Now that I have my Tags table I am trying to see how I would render the view such that it displays the tag and tag count. (it should be noted that I am trying to render this in the /views/posts/index.html.erb file). For instance, if there are 10 entries in the Tag table for tag_name Sports. How can I display Sports (10) in the view. I am not looking to do this for a specific tag but rather, somehow search the table, combine like tags and display a list of all tags with counts next to them. (I really want these to be a link to a list of posts that contain that tag but I learned early on only to ask one question at a time). Hope that makes sense.

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• Instantiate a javascript module only one time.

  - by Cedric Dugas

  Hey guys, I follow a module pattern where I instantiate components, however, a lot of time a component will only be instantiate one time (example: a comment system for an article). For now I instantiate in the same JS file. but I was wondering if it is the wrong approach? It kind of make no sense to instantiate in the same file and always only once. But at the same time, if this file is in the page I want to have access to my module without instantiate from elsewhere, and IF I need another instance, I just create another from elsewhere... Here is the pattern I follow: ApplicationNamespace.Classname = function() { // constructor function privateFunctionInit() { // private } this.privilegedFunction = function() { // privileged privateFunction(); }; privateFunctionInit() }; ApplicationNamespace.Classname.prototype = { Method: function(){} } var class = new ApplicationNamespace.Classname(); What do you think, wrong approach, or is this good?

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• Array-size macro that rejects pointers

  - by nneonneo

  The standard array-size macro that is often taught is #define ARRAYSIZE(arr) (sizeof(arr) / sizeof(arr[0])) or some equivalent formation. However, this kind of thing silently succeeds when a pointer is passed in, and gives results that can seem plausible at runtime until things mysteriously fall apart. It's all-too-easy to make this mistake: a function that has a local array variable is refactored, moving a bit of array manipulation into a new function called with the array as a parameter. So, the question is: is there a "sanitary" macro to detect misuse of the ARRAYSIZE macro in C, preferably at compile-time? In C++ we'd just use a template specialized for array arguments only; in C, it seems we'll need some way to distinguish arrays and pointers. (If I wanted to reject arrays, for instance, I'd just do e.g. (arr=arr, ...) because array assignment is illegal).

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• UItabbar settitlecolor,iPhone

  - by FirstTimer

  I am trying to change the color of the text of tabbar item,programmatically. I am using [[UITabBar appearance] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys: [UIFont fontWithName:@"AmericanTypewriter" size:20.0f], UITextAttributeFont, [UIColor blackColor], UITextAttributeTextColor, [UIColor grayColor], UITextAttributeTextShadowColor, [NSValue valueWithUIOffset:UIOffsetMake(0.0f, 1.0f)], UITextAttributeTextShadowOffset, nil]]; Which should works on iOS5 and above. But my apps gets crashed with error at console : *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_UIAppearance setTitleTextAttributes:]: unrecognized selector sent to instance 0x79f5790' *** First throw call stack: Not sure, why i am getting a crash. Also please suggest, if there is any other way to change the font color of the tabbar items. Thanks

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• WPF: Menu items and combo boxes don't render in Windows 7 64-bit

  - by lilserf

  I'm trying to use an existing internal WPF application (I do have access to the source), but it was developed on XP and I'm using Windows7 64-bit. When I click (for instance) the File menu, 90% of the time I see no drop-down menu at all. The menu still exists - I can use the arrow keys to navigate up and down and choose an option if I happen to know the order of the options, but nothing renders at all. The other 10% of the time, the menu or some portion of it DOES render, but as I move the cursor up and down I get graphical corruption or disappearing options until I end up back at the "no menu is visible at all" state. This is also true of combo boxes within the application - they show no data when I drop them down, but I can arrow down and choose an entry. Microsoft has some advice about WPF rendering issues here but none of these steps has helped with my issue.

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• Delphi : What is the best way for passing data between forms?

  - by Flom Enol

  It may seem a little newbie, but I really have got problem with it. I have a form (not the main one)for getting many different data form the user and I want to pass it to a manager class for creating an object with these. The problem is that I can't have this class to use the other unit (getting circle uses) and also it doesn't have access to the manager class instance (which is in main form). So, what shall I do? I've already considered using public variable but I have a bad feeling about it (regarding OOD patterns). Any ideas? thanks in advance.

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• jQuery dialog box not opening 2nd time

  - by Steven

  I found this thread which basically has the same issue I have. But their solution is not working for me. The dialog appears the first time I click the submit button, but not the 2nd time. I'm opening the dialog box after a form submission. UPDATE I finally got it working. Here is the correct code: if (jQuery('#registrationforms').length > 0) { //instantiate the dialog jQuery("#dialog").dialog({ modal:true, autoOpen:false }); //Some more code here to call processRegistration function. } function processRegistration(instanceID, formData) { jQuery.post("mypath/jquery_bll.php", { instance: 'processRegistration', formData : formData, instanceID : instanceID }, function(feedback) { jQuery('#dialog').text(feedback.message); jQuery('#dialog').parent().addClass(feedback.type); jQuery('#dialog').dialog('open'); },"json"); } Since I'm dynamically applying css class, I have to make sure to add it to the outer DIV which $.dialog creates to wrap my 'dialog' DIV.

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• Does HTML5 only replace the video aspects of Flash/Silverlight?

  - by John

  I see a lot of talk how HTML5 video tag will kill Flash. But while video is the most widely used part of Flash/SL, it's only a small part of their technical abilities. For instance you can write a game using full 3D graphics and socket connections in Flex, and serious business applications, etc. Is the thinking that Javascript will kill those parts of Flash/Flex/SL? Because while that seems feasible now for even quite rich web-apps, what about any kind of high-performance app like real-time graphics?

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• Makefile automatic link dependency ?

  - by Kuang Chen

  It's easy to let program figure out the dependency at compile time, (with gcc -MM). Nevertheless, link dependency (deciding which libraries should be linked to) seems to be difficult to figure out. This issue become emergent when multiple targets with individual libraries to link to are needed. For instance, three dynamic library targets t1.so, t2.so and t3.so needs to be built. t1.so needs math library (-lm), while t2 and t3 don't. It would be tedious to write separate rules. A single rule requiring the three targets linked with math library saves the trouble. However, it causes inflation of target size since math library is unused for t2.so and t3.so. Any ideas?

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• CALayer not obeying object ownership rules?

  - by eaigner

  I have a custom CALayer - UIProgressLayer - for simulating a progress bar. There is a dispatched GC timer involved to animate its intermediate state. So thats the layer I'm talking about here, although i don't think the problem is restricted to this particular subclass because a CALayer with only the -release and -dealloc overridden produces the same outcome. The problem is when i send this layer, for instance, a theLayer.opacity = 0.5f a -release message is sent to the layer, thus deallocating my layer. Why is this happening? Has it something to do with how the whole CA system works? But it still has to obey the object ownership rules right? I was thinking maybe it creates a copy of that layer for the fading, but that's not the case.

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• How do I get every nth row in a table, or how do I break up a subset of a table into sets or rows of

  - by Jherico

  I have a table of heterogeneous pieces of data identified by a primary key (ID) and a type identifier (TYPE_ID). I would like to be able to perform a query that returns me a set of ranges for a given type broken into even page sizes. For instance, if there are 10,000 records of type '1' and I specify a page size of 1000, I want 10 pairs of numbers back representing values I can use in a BETWEEN clause in subsequent queries to query the DB 1000 records at a time. My initial attempt was something like this select id, rownum from CONTENT_TABLE where type_id = ? and mod(rownum, ?) = 0 But this doesn't work.

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• NSMutableRequest skd problem

  - by user2164

  Hi, I am trying to make a web call with the iPhone. I have done this before and it works fine but now I can't make it work. I am trying to use the following method call which the documentation says is availble in 2.0 and later: - (void)addValue:(NSString *)value forHTTPHeaderField:(NSString *)field; I am attempting to build for version 3.2 and 4.0. NSMutableURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:30]; [request addValue:@"0" forHTTPHeaderField:@"Content-Length"]; The error that I'm getting is a runtime error that says "-[NSURLRequest addValue:forHTTPHeaderField:]: unrecognized selector sent to instance 0x600e0c0" Can anyone tell me what I am missing that stops this code from working? Thanks.

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• Extending appengine's db.Property with caching

  - by Noio

  I'm looking to implement a property class for appengine, very similar to the existing db.ReferenceProperty. I am implementing my own version because I want some other default return values. My question is, how do I make the property remember its returned value, so that the datastore query is only performed the first time the property is fetched? What I had is below, and it does not work. I read that the Property classes do not belong to the instances, but to the model definition, so I guess that the return value is not cached for each instance, but overwritten on the model every time. Where should I store this _resolved variable? class PageProperty(db.Property): data_type = Page def get_value_for_datastore(self, model_instance): page = super(PageProperty, self).get_value_for_datastore(model_instance) self._resolved = page return page.key().name() def make_value_from_datastore(self, value): if not hasattr(self, '_resolved'): self._resolved = Page.get_by_name(value) return self._resolved

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• using setSfGuardUser() to save the current user in the model

  - by user334017

  My application makes use of the sfGuardUser plugin. One of my tables has a relation onto the sf_guard_user table so there is a corresponding setSfGuardUser() function in the base model. From Actions.class.php, I am attempting to set the current user into the object using this function, (Which I then save in the database). my attempt: ->setSfGuardUser($this->getUser()); //called from inside Actions.class.php this throws an error: Couldn't call Doctrine_Core::set(), second argument should be an instance of Doctrine_Record or Doctrine_Null when setting one-to-one references. ...# at Doctrine_Record->coreSetRelated('sfGuardUser', object('myUser')) Which makes me think that getUser() is not returning a sfGuardUser object, though I don't know how to check this. Can anyone offer any insight?

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• Do private classes need to be accessed by properties?

  - by Andy

  I am using an instance of a private class as the state object supplied to a stream.BeginRead operation. (The class is private to my main stream reading/writing class.) public class MainClass { // ... private class ResponseState { public IResponse response; public Stream stream; public byte[] buffer = new byte[1024]; } } Access to the class is via the fields directly. Should I really be providing access to the class via properties in this case, even though it is only to be used for holding state? Interested to know what others do.

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• jQuery sanitizing comments and linkifying URLs

  - by iWasRobbed

  In terms of jQuery (or Javascript), what happens behind the scenes when a person posts a comment on Facebook, Twitter, or a blog? For instance, do they sanitize the text first, and then pattern match URL's into an actual link? Are there other items of concern that the client-side should check in addition to doing some checks on the backend? I have found a few regex's for turning URL's into links, but I'm not sure if there are better solutions. I'm trying to wrap my head around the problem, but I'm having a difficult time knowing where to start. Any guidance you can provide is greatly appreciated!

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• Can I Select and Update at the same time?

  - by Ed Manet

  This is an over-simplified explanation of what I'm working on. I have a table with status column. Multiple instances of the application will pull the contents of the first row with a status of NEW, update the status to WORKING and then go to work on the contents. It's easy enough to do this with two database calls; first the SELECT then the UPDATE. But I want to do it all in one call so that another instance of the application doesn't pull the same row. Sort of like a SELECT_AND_UPDATE thing. Is a stored procedure the best way to go?

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• How can I declare a pointer structure using {}?

  - by Y_Y

  This probably is one of the easiest question ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head and still leave it out in the global scope? For example: //not legal!!! struct node *head = {10,&head,&head};

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