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  • Deal with undefined values in code or in the template?

    - by David
    I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so: class Comment: user = ... # other stuff where user is an instance of another class, class User: name = ... # other stuff And of course in my template, I have <div>${comment.user.name}</div> Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities: Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer. Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error. Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?) Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.

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  • How can I read JSON file from disk and store to array in Swift

    - by Ezekiel Elin
    I want to read a file from Disk in a swift file. It can be a relative or direct path, that doesn't matter. How can I do that? I've been playing with something like this let classesData = NSData .dataWithContentsOfMappedFile("path/to/classes.json"); And it finds the file (i.e. doesn't return nil) but I don't know how to manipulate and convert to JSON, the data returned. It isn't in a string format and String() isn't working on it.

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  • Reverse engineering a bezier curve

    - by Martin
    Given a few sample points on a bézier curve, is it possible to work out the set of possible parameters of the curve? In my specific application there is a limited set of endpoints the curve may have, so I want to generate the set of possible curves, enumerate all of them and pick out all the ones which may end on a valid end point.

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  • Finding the maximum weight subsequence of an array of positive integers?

    - by BeeBand
    I'm tring to find the maximum weight subsequence of an array of positive integers - the catch is that no adjacent members are allowed in the final subsequence. The exact same question was asked here, and a recursive solution was given by MarkusQ. He provides an explanation, but can anyone help me understand how he has expanded the function? How does this solution take into consideration non-adjacent members?

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  • How does Amazon's Statistically Improbable Phrases work?

    - by ??iu
    How does something like Statistically Improbable Phrases work? According to amazon: Amazon.com's Statistically Improbable Phrases, or "SIPs", are the most distinctive phrases in the text of books in the Search Inside!™ program. To identify SIPs, our computers scan the text of all books in the Search Inside! program. If they find a phrase that occurs a large number of times in a particular book relative to all Search Inside! books, that phrase is a SIP in that book. SIPs are not necessarily improbable within a particular book, but they are improbable relative to all books in Search Inside!. For example, most SIPs for a book on taxes are tax related. But because we display SIPs in order of their improbability score, the first SIPs will be on tax topics that this book mentions more often than other tax books. For works of fiction, SIPs tend to be distinctive word combinations that often hint at important plot elements. For instance, for Joel's first book, the SIPs are: leaky abstractions, antialiased text, own dog food, bug count, daily builds, bug database, software schedules One interesting complication is that these are phrases of either 2 or 3 words. This makes things a little more interesting because these phrases can overlap with or contain each other.

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  • Why does C# allow abstract class with no abstract members?

    - by fatcat1111
    The C# spec, section 10.1.1.1, states: An abstract class is permitted (but not required) to contain abstract members. This allows me to create classes like this: public abstract class A { public void Main() { // it's full of logic! } } This is really a concrete class; it's only abstract in so far as one can't instantiate it. If inheritors don't actually have to provide implementation, then why call it abstract?

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  • Transliteration API: Is it possible to make all input fields in the page transliteratable?

    - by SolidSnakeGTI
    Hello, I've used "Google AJAX Transliteration API" and it's going well with me. http://code.google.com/apis/ajaxlanguage/documentation/referenceTransliteration.html Currently I've a project that I need all input fields in every page (input & textarea tags) to be transliteratable, while these input fields differs from page to page (dynamic). As I know, I've to call makeTransliteratable(elementIds, opt_options) method in the API call to define which input fields to make transliteratable, and in my case here I can't predefine those fields manually. Is there a way to achieve this? Thanks in advance

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  • Why are compilers so stupid?

    - by martinus
    I always wonder why compilers can't figure out simple things that are obvious to the human eye. They do lots of simple optimizations, but never something even a little bit complex. For example, this code takes about 6 seconds on my computer to print the value zero (using java 1.6): int x = 0; for (int i = 0; i < 100 * 1000 * 1000 * 1000; ++i) { x += x + x + x + x + x; } System.out.println(x); It is totally obvious that x is never changed so no matter how often you add 0 to itself it stays zero. So the compiler could in theory replace this with System.out.println(0). Or even better, this takes 23 seconds: public int slow() { String s = "x"; for (int i = 0; i < 100000; ++i) { s += "x"; } return 10; } First the compiler could notice that I am actually creating a string s of 100000 "x" so it could automatically use s StringBuilder instead, or even better directly replace it with the resulting string as it is always the same. Second, It does not recognize that I do not actually use the string at all, so the whole loop could be discarded! Why, after so much manpower is going into fast compilers, are they still so relatively dumb? EDIT: Of course these are stupid examples that should never be used anywhere. But whenever I have to rewrite a beautiful and very readable code into something unreadable so that the compiler is happy and produces fast code, I wonder why compilers or some other automated tool can't do this work for me.

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  • How to deal with forward declaration / #import in Cocoa Touch (Objective-C cross C++) correctly?

    - by unknownthreat
    I am trying to write this header file: //@class AQPlayer; //#import "AQPlayer.h" @interface AQ_PWN_iPhoneViewController : UIViewController { AQPlayer* player; } @end AQPlayer is a .mm file written in C++. I tried to make a class forward declaration here, but it complains to me: error: cannot find interface declaration for 'AQPlayer' So I tried to "#import" the header file instead, but it complains something completely off and weird. Here's a slice of the error complained: In file included from /Users/akaraphan/Desktop/SpecialTopic1/AQ_PWN_iPhone/Classes/AQPlayer.h:51, from /Users/akaraphan/Desktop/SpecialTopic1/AQ_PWN_iPhone/Classes/AQ_PWN_iPhoneViewController.h:12, from /Users/akaraphan/Desktop/SpecialTopic1/AQ_PWN_iPhone/Classes/AQ_PWN_iPhoneAppDelegate.m:10: /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:78: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAStreamBasicDescription' /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:230: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:231: error: expected '=', ',', ';', 'asm' or '__attribute__' before '==' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:233: error: expected '=', ',', ';', 'asm' or '__attribute__' before '!=' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:234: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<=' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:235: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>=' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:236: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:239: error: expected ';', ',' or ')' before '&' token Am I missing something? Can't I do a forward declaration for this?

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  • How can I convert German characters during XML read and PHP write into mysql?

    - by kitenski
    Morning, I am inputting data from an XML file into my database, but have any isse with German words (that are in the XML by mistake) For example the word für appears in my XML as für and thus appears the same in my database. I know I could do a simple search/replace for that exact phrase, but I was wondering if there was a smarter way to do it as I can't predict if any other German words may one day appear in the XML? ADDING SOME MORE DETAIL The XML source says: and in my PHP I have $domString = utf8_encode($dom-saveXML($element)); If I look into the XML file before I start reading it, it has - <title> - <![CDATA[ CoPilot Live v8 Europa für Android 8.0.0.644 ]]> </title> Thanks. Greg

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  • Throwing cats out of windows

    - by AndrewF
    Imagine you're in a tall building with a cat. The cat can survive a fall out of a low story window, but will die if thrown from a high floor. How can you figure out the longest drop that the cat can survive, using the least number of attempts? Obviously, if you only have one cat, then you can only search linearly. First throw the cat from the first floor. If it survives, throw it from the second. Eventually, after being thrown from floor f, the cat will die. You then know that floor f-1 was the maximal safe floor. But what if you have more than one cat? You can now try some sort of logarithmic search. Let's say that the build has 100 floors and you have two identical cats. If you throw the first cat out of the 50th floor and it dies, then you only have to search 50 floors linearly. You can do even better if you choose a lower floor for your first attempt. Let's say that you choose to tackle the problem 20 floors at a time and that the first fatal floor is #50. In that case, your first cat will survive flights from floors 20 and 40 before dying from floor 60. You just have to check floors 41 through 49 individually. That's a total of 12 attempts, which is much better than the 50 you would need had you attempted to use binary elimination. In general, what's the best strategy and it's worst-case complexity for an n-storied building with 2 cats? What about for n floors and m cats? Assume that all cats are equivalent: they will all survive or die from a fall from a given window. Also, every attempt is independent: if a cat survives a fall, it is completely unharmed. This isn't homework, although I may have solved it for school assignment once. It's just a whimsical problem that popped into my head today and I don't remember the solution. Bonus points if anyone knows the name of this problem or of the solution algorithm.

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  • How to call an event when the user "finally" selects an item in a list?

    - by herzmeister der welten
    When a user clicks once on an item in a Grid or a ListBox, that item is usually selected, hence most UI frameworks have a onSelected event or the like for that. However, how can we generally call the next step when a user "finally" selects an item by e.g. double clicking an entry? You know when some popup might appear in the context of the selected item and the user can do further stuff. Strangely enough, I think I have never seen a word for that in any UI framework. onPicked, onAccepted, onChosen, onFinallySelected, onResult? All kinda awkward or too special. Any other ideas?

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  • Issue when I'm trying to draw gradient in swift

    - by bagusflyer
    I got an error when I was trying to draw gradient in Swift code: GradientView.swift:31:40: Could not find an overload for '__conversion' that accepts the supplied arguments Here is my code: let context : CGContextRef = UIGraphicsGetCurrentContext() let locations :CGFloat[] = [ 0.0, 0.25, 0.5, 0.75 ] let colors = [UIColor.redColor().CGColor,UIColor.greenColor().CGColor,UIColor.blueColor().CGColor, UIColor.yellowColor().CGColor] let colorspace : CGColorSpaceRef = CGColorSpaceCreateDeviceRGB() let gradient : CGGradientRef = CGGradientCreateWithColors(colorspace, colors, locations) //CGGradientCreateWithColors(colorspace,colors,locations) let startPoint : CGPoint = CGPointMake(0, 0) let endPoint : CGPoint = CGPointMake(500,500) CGContextDrawLinearGradient(context, gradient,startPoint, endPoint, 0); The problem is the CGGradientCreateWithColors takes CFArray not a normal Swift Array. I have no idea how to convert CFArray to Array and can't find anything in Apple's document. Any idea? Thanks

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  • Should i write my own forum? If my site has banning/PM/etc?

    - by acidzombie24
    I built a site from scratch (already done). It has banning, PM, comments, etc. The PMs and comments are done using markdown (like SO system). Should i write my own forum code or should i find one already made? What are reasons for or against writing my own? There are pros and cons for writing my own or using another software. But some cons keeping me from using another forum software is Multiple Logins: One for the site, one for separate forums. Need to Customization code: I'll need to change the toolbar in the forum software so i can access pages on the regular site. Look consistency: It may look drastically different from my site even after applying lots of css changes. Banning and User consistency. Users may be ban on site or on forums but not the other. users may select a different or multiple usernames on the forum instead of being forced to use the same username on both site and forum. What are reasons for or against writing my own and using forum software?

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  • What is the Software Development Lifecycle?

    - by j-t-s
    Our investor wants a SDLC. I've never written one before, and I don't have enough time to go and buy a book, or spend much time learning about them. From what I've been told about them, they consist of requirements (what needs to be done), and a list is done. Is this correct? Update: I have found this article which really helps to explain things in simple terms and very quickly. Not that I think an SDLC should be done quickly. In my case, I have no other option.

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  • How do actually castings work at the CLR level?

    - by devoured elysium
    When doing an upcast or downcast, what does really happen behind the scenes? I had the idea that when doing something as: string myString = "abc"; object myObject = myString; string myStringBack = (string)myObject; the cast in the last line would have as only purpose tell the compiler we are safe we are not doing anything wrong. So, I had the idea that actually no casting code would be embedded in the code itself. It seems I was wrong: .maxstack 1 .locals init ( [0] string myString, [1] object myObject, [2] string myStringBack) L_0000: nop L_0001: ldstr "abc" L_0006: stloc.0 L_0007: ldloc.0 L_0008: stloc.1 L_0009: ldloc.1 L_000a: castclass string L_000f: stloc.2 L_0010: ret Why does the CLR need something like castclass string? There are two possible implementations for a downcast: You require a castclass something. When you get to the line of code that does an castclass, the CLR tries to make the cast. But then, what would happen had I ommited the castclass string line and tried to run the code? You don't require a castclass. As all reference types have a similar internal structure, if you try to use a string on an Form instance, it will throw an exception of wrong usage (because it detects a Form is not a string or any of its subtypes). Also, is the following statamente from C# 4.0 in a Nutshell correct? Upcasting and downcasting between compatible reference types performs reference conversions: a new reference is created that points to the same object. Does it really create a new reference? I thought it'd be the same reference, only stored in a different type of variable. Thanks

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  • Make interchangeable class types via pointer casting only, without having to allocate any new objects?

    - by HostileFork
    UPDATE: I do appreciate "don't want that, want this instead" suggestions. They are useful, especially when provided in context of the motivating scenario. Still...regardless of goodness/badness, I've become curious to find a hard-and-fast "yes that can be done legally in C++11" vs "no it is not possible to do something like that". I want to "alias" an object pointer as another type, for the sole purpose of adding some helper methods. The alias cannot add data members to the underlying class (in fact, the more I can prevent that from happening the better!) All aliases are equally applicable to any object of this type...it's just helpful if the type system can hint which alias is likely the most appropriate. There should be no information about any specific alias that is ever encoded in the underlying object. Hence, I feel like you should be able to "cheat" the type system and just let it be an annotation...checked at compile time, but ultimately irrelevant to the runtime casting. Something along these lines: Node<AccessorFoo>* fooPtr = Node<AccessorFoo>::createViaFactory(); Node<AccessorBar>* barPtr = reinterpret_cast< Node<AccessorBar>* >(fooPtr); Under the hood, the factory method is actually making a NodeBase class, and then using a similar reinterpret_cast to return it as a Node<AccessorFoo>*. The easy way to avoid this is to make these lightweight classes that wrap nodes and are passed around by value. Thus you don't need casting, just Accessor classes that take the node handle to wrap in their constructor: AccessorFoo foo (NodeBase::createViaFactory()); AccessorBar bar (foo.getNode()); But if I don't have to pay for all that, I don't want to. That would involve--for instance--making a special accessor type for each sort of wrapped pointer (AccessorFooShared, AccessorFooUnique, AccessorFooWeak, etc.) Having these typed pointers being aliased for one single pointer-based object identity is preferable, and provides a nice orthogonality. So back to that original question: Node<AccessorFoo>* fooPtr = Node<AccessorFoo>::createViaFactory(); Node<AccessorBar>* barPtr = reinterpret_cast< Node<AccessorBar>* >(fooPtr); Seems like there would be some way to do this that might be ugly but not "break the rules". According to ISO14882:2011(e) 5.2.10-7: An object pointer can be explicitly converted to an object pointer of a different type.70 When a prvalue v of type "pointer to T1" is converted to the type "pointer to cv T2", the result is static_cast(static_cast(v)) if both T1 and T2 are standard-layout types (3.9) and the alignment requirements of T2 are no stricter than those of T1, or if either type is void. Converting a prvalue of type "pointer to T1" to the type "pointer to T2" (where T1 and T2 are object types and where the alignment requirements of T2 are no stricter than those of T1) and back to its original type yields the original pointer value. The result of any other such pointer conversion is unspecified. Drilling into the definition of a "standard-layout class", we find: has no non-static data members of type non-standard-layout-class (or array of such types) or reference, and has no virtual functions (10.3) and no virtual base classes (10.1), and has the same access control (clause 11) for all non-static data members, and has no non-standard-layout base classes, and either has no non-static data member in the most-derived class and at most one base class with non-static data members, or has no base classes with non-static data members, and has no base classes of the same type as the first non-static data member. Sounds like working with something like this would tie my hands a bit with no virtual methods in the accessors or the node. Yet C++11 apparently has std::is_standard_layout to keep things checked. Can this be done safely? Appears to work in gcc-4.7, but I'd like to be sure I'm not invoking undefined behavior.

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  • Can i change the view without changing the controller?

    - by Ian Boyd
    Pretend1 there is a place to type in a name:     Name: __________________ When the text box changes, the value is absorbed into the controller, who stores it in data model. Business rules require that a name be entered: if there is no text entered the TextBox should be colored something in the view to indicate baddness; otherwise it can be whatever color the view likes. The TextBox contains a String, the controller handles a String, and the model stores a String. Now lets say i want to improve the view. There is a new kind of text box2 that can be fed not only string-based keyboard input, but also an image. The view (currently) knows how to determine if the image is in the proper format to perform the processing required to extract text out of it. If there is text, then that text can be fed to the controller, who feeds it to the data model. But if the image is invalid, e.g.3 wrong file format invalid dimensions invalid bit depth unhandled or unknown encoding format missing or incorrectly located registration marks contents not recognizable the view can show something to the user that the image is bad. But the telling the user that something is bad is supposed to be the job of the controller. i'm, of course, not going to re-write the controller to handle Image based text-input (e.g. image based names). a. the code is binary locked inside a GUI widget4 b. there other views besides this one, i'm not going to impose a particular view onto the controller c. i just don't wanna. If i have to change things outside of this UI improvement, then i'll just leave the UI unimproved5 So what's the thinking on having different views for the same Model and Controller? Nitpicker's Corner 1 contrived hypothetical example 2 e.g. bar code, g-mask, ocr 3 contrived hypothetical reasons 4 or hardware of a USB bar-code scanner 5 forcing the user to continue to use a DateTimePicker rather than a TextBox

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