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  • What are the benefits of prototypal inheritance over classical?

    - by Pierreten
    So I finally stopped dragging my feet all these years and decided to learn JavaScript "properly". One of the most head-scratching elements of the languages design is it's implementation of inheritance. Having experience in Ruby, I was really happy to see closures and dynamic typing; but for the life of me can't figure out what benefits are to be had from object instances using other instances for inheritance.

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  • Python script to calculate aded combinations from a dictionary

    - by dayde
    I am trying to write a script that will take a dictionary of items, each containing properties of values from 0 - 10, and add the various elements to select which combination of items achieve the desired totals. I also need the script to do this, using only items that have the same "slot" in common. For example: item_list = { 'item_1': {'slot': 'top', 'prop_a': 2, 'prop_b': 0, 'prop_c': 2, 'prop_d': 1 }, 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 }, 'item_3': {'slot': 'top', 'prop_a': 2, 'prop_b': 5, 'prop_c': 2, 'prop_d':-2 }, 'item_4': {'slot': 'mid', 'prop_a': 5, 'prop_b': 5, 'prop_c':-5, 'prop_d': 0 }, 'item_5': {'slot': 'mid', 'prop_a':10, 'prop_b': 0, 'prop_c':-5, 'prop_d': 0 }, 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 }, 'item_7': {'slot': 'bot', 'prop_a': 1, 'prop_b': 3, 'prop_c':-4, 'prop_d': 4 }, 'item_8': {'slot': 'bot', 'prop_a': 2, 'prop_b': 2, 'prop_c': 0, 'prop_d': 0 }, 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 }, } The script would then need to select which combinations from the "item_list" dict that using 1 item per "slot" that would achieve a desired result when added. For example, if the desired result was: 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0, the script would select 'item_2', 'item_6', and 'item_9', along with any other combination that worked. 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 } 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 } 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 } 'total': 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0 Any ideas how to accomplish this? It does not need to be in python, or even a thorough script, but just an explanation on how to do this in theory would be enough for me. I have tried working out looping through every combination, but that seems to very quickly get our of hand and unmanageable. The actual script will need to do this for about 1,000 items using 20 different "slots", each with 8 properties. Thanks for the help!

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  • Generating easy-to-remember random identifiers

    - by Carl Seleborg
    Hi all, As all developers do, we constantly deal with some kind of identifiers as part of our daily work. Most of the time, it's about bugs or support tickets. Our software, upon detecting a bug, creates a package that has a name formatted from a timestamp and a version number, which is a cheap way of creating reasonably unique identifiers to avoid mixing packages up. Example: "Bug Report 20101214 174856 6.4b2". My brain just isn't that good at remembering numbers. What I would love to have is a simple way of generating alpha-numeric identifiers that are easy to remember. Examples would be "azil3", "ulmops", "fel2way", etc. I just made these up, but they are much easier to recognize when you see many of them at once. I know of algorithms that perform trigram analysis on text (say you feed them a whole book in German) and that can generate strings that look and feel like German words. This requires lots of data, though, and makes it slightly less suitable for embedding in an application just for this purpose. Do you know of anything else? Thanks! Carl

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  • Code Golf: Rotating Maze

    - by trinithis
    Code Golf: Rotating Maze Make a program that takes in a file consisting of a maze. The maze has walls given by '#'. The maze must include a single ball, given by a 'o' and any number of holes given by a '@'. The maze file can either be entered via command line or read in as a line through standard input. Please specify which in your solution. Your program then does the following: 1: If the ball is not directly above a wall, drop it down to the nearest wall. 2: If the ball passes through a hole during step 1, remove the ball. 3: Display the maze. 4: If there is no ball in the maze, exit. 5: Read a line from the standard input. Given a 1, rotate the maze counterclockwise. Given a 2, rotate the maze clockwise. Rotations are done by 90 degrees. It is up to you to decide if extraneous whitespace is allowed. If the user enters other inputs, repeat this step. 6: Goto step 1. You may assume all input mazes are closed. Note, a hole effectively acts as a wall in this regard. You may assume all input mazes have no extraneous whitespace. The shortest source code by character count wins. Example mazes: ###### #o @# ###### ########### #o # # ####### # ###@ # ######### ########################### # # # # @ # # # # ## # # ####o#### # # # # # # ######### # @ ######################

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  • What should I call a class that contains a sequence of states

    - by Robert P
    I have a GUI tool that manages state sequences. One component is a class that contains a set of states, your typical DFA state machine. For now, I'll call this a StateSet. However, I have another class that has a collection (possibly partially unordered) of those state sets, and lists them in a particular order. and I'm trying to come up with a good name for it - not just for internal code, but for customers to refer to it. I've got: Sequence (maybe) StateSetSet (reasonable for code, but not for customers) Any other suggestions or 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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  • Regular expressions - finding and comparing the first instance of a word

    - by Dan
    Hi there, I am currently trying to write a regular expression to pull links out of a page I have. The problem is the links need to be pulled out only if the links have 'stock' for example. This is an outline of what I have code wise: <td class="prd-details"> <a href="somepage"> ... <span class="collect unavailable"> </td> <td class="prd-details"> <a href="somepage"> ... <span class="collect available"> </td> What I would like to do is pull out the links only if 'collect available' is in the tag. I have tried to do this with the regular expression: (?s)prd-details[^=]+="([^"]+)" .+?collect{1}[^\s]+ available However on running it, it will find the first 'prd-details' class and keep going until it finds 'collect available', thereby taking the incorrect results. I thought by specifying the {1} after the word collect it would only use the first instance of the word it finds, but apparently I'm wrong. I've been trying to use different things such as positive and negative lookaheads but I cant seem to get anything to work. Might anyone be able to help me with this issue? Thanks, Dan

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  • Formal Equivalence between programming languages

    - by Ketan
    Hello We have 2 languages which are (informally) semantically equivalent but syntactically different. One is xml and another is script based. How can I go about formally proving that both languages are in fact equivalent. Script approach is just a convenient way to write a same program that would be tedious to write in xml. Thanks Ketan

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  • How should i organize authority code?

    - by acidzombie24
    I have users that fall into the following Not logged in Not Verified Verified Moderator Admin All code that only admin and moderators can access (like banning) is in ModeratorUser which inherits from verified which inherits from BaseUser. Some pages are accessible to all users such as public profiles. If a user is logged in he can leave a comment. To check this i use if (IsVerifiedUser). Now here is the problem. To avoid problems if a user is banned he is not recognized as a verified user. However in the rare case i need to know if he is verified i can use usertype & Verified. Should i not be doing this? I have a bunch of code in my VerifiedUser class and find i am moving tons of it to BaseUser. Is this something i help because a not logged in user can access the page? Should i handle the ban user in a different way and allow IsVerifiedUser to be true even if the user is banned?

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  • An Ideal Keyboard Layout for Programming

    - by Jon Purdy
    I often hear complaints that programming languages that make heavy use of symbols for brevity, most notably C and C++ (I'm not going to touch APL), are difficult to type because they require frequent use of the shift key. A year or two ago, I got tired of it myself, downloaded Microsoft's Keyboard Layout Creator, made a few changes to my layout, and have not once looked back. The speed difference is astounding; with these few simple changes I am able to type C++ code around 30% faster, depending of course on how hairy it is; best of all, my typing speed in ordinary running text is not compromised. My questions are these: what alternate keyboard layouts have existed for programming, which have gained popularity, are any of them still in modern use, do you personally use any altered layout, and how can my layout be further optimised? I made the following changes to a standard QWERTY layout. (I don't use Dvorak, but there is a programmer Dvorak layout worth mentioning.) Swap numbers with symbols in the top row, because long or repeated literal numbers are typically replaced with named constants; Swap backquote with tilde, because backquotes are rare in many languages but destructors are common in C++; Swap minus with underscore, because underscores are common in identifiers; Swap curly braces with square brackets, because blocks are more common than subscripts; and Swap double quote with single quote, because strings are more common than character literals. I suspect this last is probably going to be the most controversial, as it interferes the most with running text by requiring use of shift to type common contractions. This layout has significantly increased my typing speed in C++, C, Java, and Perl, and somewhat increased it in LISP and Python.

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  • Code-Golf: Friendly Number Abbreviator

    - by David Murdoch
    Based on this question: Is there a way to round numbers into a friendly format? THE CHALLENGE - UPDATED! (removed hundreds abbreviation from spec) The shortest code by character count that will abbreviate an integer (no decimals). Code should include the full program. Relevant range is from 0 - 9,223,372,036,854,775,807 (the upper limit for signed 64 bit integer). The number of decimal places for abbreviation will be positive. You will not need to calculate the following: 920535 abbreviated -1 place (which would be something like 0.920535M). Numbers in the tens and hundreds place (0-999) should never be abbreviated (the abbreviation for the number 57 to 1+ decimal places is 5.7dk - it is unneccessary and not friendly). Remember to round half away from zero (23.5 gets rounded to 24). Banker's rounding is verboten. Here are the relevant number abbreviations: h = hundred (102) k = thousand (103) M = million (106) G = billion (109) T = trillion (1012) P = quadrillion (1015) E = quintillion (1018) SAMPLE INPUTS/OUTPUTS (inputs can be passed as separate arguments): First argument will be the integer to abbreviate. The second is the number of decimal places. 12 1 => 12 // tens and hundreds places are never rounded 1500 2 => 1.5k 1500 0 => 2k // look, ma! I round UP at .5 0 2 => 0 1234 0 => 1k 34567 2 => 34.57k 918395 1 => 918.4k 2134124 2 => 2.13M 47475782130 2 => 47.48G 9223372036854775807 3 => 9.223E // ect... . . . Original answer from related question (javascript, does not follow spec): function abbrNum(number, decPlaces) { // 2 decimal places => 100, 3 => 1000, etc decPlaces = Math.pow(10,decPlaces); // Enumerate number abbreviations var abbrev = [ "k", "m", "b", "t" ]; // Go through the array backwards, so we do the largest first for (var i=abbrev.length-1; i>=0; i--) { // Convert array index to "1000", "1000000", etc var size = Math.pow(10,(i+1)*3); // If the number is bigger or equal do the abbreviation if(size <= number) { // Here, we multiply by decPlaces, round, and then divide by decPlaces. // This gives us nice rounding to a particular decimal place. number = Math.round(number*decPlaces/size)/decPlaces; // Add the letter for the abbreviation number += abbrev[i]; // We are done... stop break; } } return number; }

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  • Is using a FSM a good design for general text parsing?

    - by eSKay
    I am reading a file that is filled with hex numbers. I have to identify a particular pattern, say "aaad" (without quotes) from it. Every time I see the pattern, I generate some data to some other file. This would be a very common case in designing programs - parsing and looking for a particular pattern. I have designed it as a Finite State Machine and structured structured it in C using switch-case to change states. This was the first implementation that occured to me. DESIGN: Are there some better designs possible? IMPLEMENTATION: Do you see some problems with using a switch case as I mentioned?

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  • any character notation for php regular expression

    - by Mith
    In my regex, I want to say that within the sample text, any characters are allowed, including a-z in upper and lower case, numbers and special characters. For example, my regular expression may be checking that a document is html. therefore: "/[]+/" i have tried []+ but it does not seem to like this?

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  • What is the purpose of Java's unary plus operator?

    - by Syntactic
    Java's unary plus operator appears to have come over from C, via C++. As near as I can tell, it has the following effects: promotes its operand to int, if it's not already an int or wider unboxes its operand, if it's a wrapper object complicates slightly the parsing of evil expressions containing large numbers of consecutive plus signs It seems to me that there are better (or, at least, clearer) ways to do all of these things. In this SO question, concerning the counterpart operator in C#, someone said that "It's there to be overloaded if you feel the need." But in Java, one cannot overload any operator. So does this operator exist in Java just because it existed in C++?

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  • A two way minimum spanning tree of a directed graph

    - by mvid
    Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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  • C: 8x8 -> 16 bit multiply precision guaranteed by integer promotions?

    - by craig-blome
    I'm trying to figure out if the C Standard (C90, though I'm working off Derek Jones' annotated C99 book) guarantees that I will not lose precision multiplying two unsigned 8-bit values and storing to a 16-bit result. An example statement is as follows: unsigned char foo; unsigned int foo_u16 = foo * 10; Our Keil 8051 compiler (v7.50 at present) will generate a MUL AB instruction which stores the MSB in the B register and the LSB in the accumulator. If I cast foo to a unsigned int first: unsigned int foo_u16 = (unsigned int)foo * 10; then the compiler correctly decides I want a unsigned int there and generates an expensive call to a 16x16 bit integer multiply routine. I would like to argue beyond reasonable doubt that this defensive measure is not necessary. As I read the integer promotions described in 6.3.1.1, the effect of the first line shall be as if foo and 10 were promoted to unsigned int, the multiplication performed, and the result stored as unsigned int in foo_u16. If the compiler knows an instruction that does 8x8-16 bit multiplications without loss of precision, so much the better; but the precision is guaranteed. Am I reading this correctly? Best regards, Craig Blome

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  • How to balance number of ratings versus the ratings themselves?

    - by zneak
    Hello guys, For a school project, we'll have to implement a ranking system. However, we figured that a dumb rank average would suck: something that one user ranked 5 stars would have a better average that something 188 users ranked 4 stars, and that's just stupid. So I'm wondering if any of you have an example algorithm of "smart" ranking. It only needs to take in account the rankings given and the number of rankings. Thanks!

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  • What do we log and why do we log it?

    - by Lucas
    This has been bugging me for quite some time. Reading various questions on SO, blogs and listening to colleagues, I keep hearing how important "logging" is. How various logging frameworks stack up against each other, and how there are so many to pick from it's (apparently) ridiculous. Now, I know what logging is. What I don't know is what is supposed to be logged and why. Sure, I can guess. Exceptions? Sounds like something one might want to log... but which exceptions? And is it only exceptions? And what do I do with the logged information? If it's an in-house app, then that could probably be put to good use, but if it's a commercial desktop application, how is the log of... whatever... helping anyone? I doubt regular users would be peeking inside. Is it then something you ask the users to provide on request? I'm deeply frustrated by my own ignorance in this. It's also surprising how little information there is about this. The info on the websites of the various logging frameworks is all written for an audience that already knows what it wants to log, and knows why it needs to do so. Same things goes for the various discussions on SO about logging, like for instance this highly voted up question on Logging best practices. For a question with so many votes, it's almost comical how there's next to nothing in there that would answer my what and why questions. So being finally fed up, I'm asking here: what do people log, and why do they log it?

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  • Is it possible to create thread-safe collections without locks?

    - by Andrey
    This is pure just for interest question, any sort of questions are welcome. So is it possible to create thread-safe collections without any locks? By locks I mean any thread synchronization mechanisms, including Mutex, Semaphore, and even Interlocked, all of them. Is it possible at user level, without calling system functions? Ok, may be implementation is not effective, i am interested in theoretical possibility. If not what is the minimum means to do it? EDIT: Why immutable collections don't work. This of class Stack with methods Add that returns another Stack. Now here is program: Stack stack = new ...; ThreadedMethod() { loop { //Do the loop stack = stack.Add(element); } } this expression stack = stack.Add(element) is not atomic, and you can overwrite new stack from other thread. Thanks, Andrey

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  • Does this data structure have a name? Sort of a "linked matrix"?

    - by Bob
    Let's say I wanted similar functionality to a doubly linked list but needed a matrix instead so that each node was structured like this: public class Node { Node Up, Down, Left, Right; object Value; } Is there a name for such a structure? I've looked through this Wikipedia listing of data structures but didn't see anything similar. Unless I just missed it.

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