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  • Language to learn metaprogramming

    - by Erup
    What's the best language (in terms of simplicity, readability and code elegancy) in your opinion, to learn and work with metaprogramming? I think metaprogramming is the "future of coding". Not saying that code will extinct, but we can see this scenario coming on new technologies.

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  • Event feed implementation - will it scale?

    - by SlappyTheFish
    Situation: I am currently designing a feed system for a social website whereby each user has a feed of their friends' activities. I have two possible methods how to generate the feeds and I would like to ask which is best in terms of ability to scale. Events from all users are collected in one central database table, event_log. Users are paired as friends in the table friends. The RDBMS we are using is MySQL. Standard method: When a user requests their feed page, the system generates the feed by inner joining event_log with friends. The result is then cached and set to timeout after 5 minutes. Scaling is achieved by varying this timeout. Hypothesised method: A task runs in the background and for each new, unprocessed item in event_log, it creates entries in the database table user_feed pairing that event with all of the users who are friends with the user who initiated the event. One table row pairs one event with one user. The problems with the standard method are well known – what if a lot of people's caches expire at the same time? The solution also does not scale well – the brief is for feeds to update as close to real-time as possible The hypothesised solution in my eyes seems much better; all processing is done offline so no user waits for a page to generate and there are no joins so database tables can be sharded across physical machines. However, if a user has 100,000 friends and creates 20 events in one session, then that results in inserting 2,000,000 rows into the database. Question: The question boils down to two points: Is this worst-case scenario mentioned above problematic, i.e. does table size have an impact on MySQL performance and are there any issues with this mass inserting of data for each event? Is there anything else I have missed?

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  • doubt in sizeof implementation

    - by aks
    Below is the program to find the size of a structure without using sizeof operator: struct MyStruct { int i; int j; }; int main() { struct MyStruct *p=0; int size = ((char*)(p+1))-((char*)p); printf("\nSIZE : [%d]\nSIZE : [%d]\n", size); return 0; } My doubt is: Why is typecasting to char * required? If I don't use the char* pointer, the output is 1 - WHY?

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  • MySQL Hashing Function Implementation

    - by Jonas Stevens
    I know that php has md5(), sha1(), and the hash() functions, but I want to create a hash using the MySQL PASSWORD() function. So far, the only way I can think of is to just query the server, but I want a function (preferably in php or Perl) that will do the same thing without querying MySQL at all. For example: MySQL hash - 464bb2cb3cf18b66 MySQL5 hash - *01D01F5CA7CA8BA771E03F4AC55EC73C11EFA229 Thanks!

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  • What's the recommended implementation for hashing OLE Variants?

    - by Barry Kelly
    OLE Variants, as used by older versions of Visual Basic and pervasively in COM Automation, can store lots of different types: basic types like integers and floats, more complicated types like strings and arrays, and all the way up to IDispatch implementations and pointers in the form of ByRef variants. Variants are also weakly typed: they convert the value to another type without warning depending on which operator you apply and what the current types are of the values passed to the operator. For example, comparing two variants, one containing the integer 1 and another containing the string "1", for equality will return True. So assuming that I'm working with variants at the underlying data level (e.g. VARIANT in C++ or TVarData in Delphi - i.e. the big union of different possible values), how should I hash variants consistently so that they obey the right rules? Rules: Variants that hash unequally should compare as unequal, both in sorting and direct equality Variants that compare as equal for both sorting and direct equality should hash as equal It's OK if I have to use different sorting and direct comparison rules in order to make the hashing fit. The way I'm currently working is I'm normalizing the variants to strings (if they fit), and treating them as strings, otherwise I'm working with the variant data as if it was an opaque blob, and hashing and comparing its raw bytes. That has some limitations, of course: numbers 1..10 sort as [1, 10, 2, ... 9] etc. This is mildly annoying, but it is consistent and it is very little work. However, I do wonder if there is an accepted practice for this problem.

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  • Is this implementation truely tail-recursive?

    - by CFP
    Hello everyone! I've come up with the following code to compute in a tail-recursive way the result of an expression such as 3 4 * 1 + cos 8 * (aka 8*cos(1+(3*4))) The code is in OCaml. I'm using a list refto emulate a stack. type token = Num of float | Fun of (float->float) | Op of (float->float->float);; let pop l = let top = (List.hd !l) in l := List.tl (!l); top;; let push x l = l := (x::!l);; let empty l = (l = []);; let pile = ref [];; let eval data = let stack = ref data in let rec _eval cont = match (pop stack) with | Num(n) -> cont n; | Fun(f) -> _eval (fun x -> cont (f x)); | Op(op) -> _eval (fun x -> cont (op x (_eval (fun y->y)))); in _eval (fun x->x) ;; eval [Fun(fun x -> x**2.); Op(fun x y -> x+.y); Num(1.); Num(3.)];; I've used continuations to ensure tail-recursion, but since my stack implements some sort of a tree, and therefore provides quite a bad interface to what should be handled as a disjoint union type, the call to my function to evaluate the left branch with an identity continuation somehow irks a little. Yet it's working perfectly, but I have the feeling than in calling the _eval (fun y->y) bit, there must be something wrong happening, since it doesn't seem that this call can replace the previous one in the stack structure... Am I misunderstanding something here? I mean, I understand that with only the first call to _eval there wouldn't be any problem optimizing the calls, but here it seems to me that evaluation the _eval (fun y->y) will require to be stacked up, and therefore will fill the stack, possibly leading to an overflow... Thanks!

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  • Cross-Browser jQuery text-zoom implementation

    - by JMC Creative
    I've got some code to increase/decrease font size. This is giving me a headache because each browser seems to implement the $.css('font-size') differently (see jquery bug). The part that's really killing me, though, is that Firefox is scaling up okay, but when I use the scale down function below, it scales up. Webkit & IE are both working as expected. Any ideas on that? I put this in a fiddle here: http://jsfiddle.net/srQ3P/1/ where you can see it working as expected, and you can see it broken in firefox at the project page: http://cumberlandme.info/residents MAJOR EDIT Sorry, the issue is not the code, it's firefox buggy behavior. After I zoom in or out with the browser controls (ctrl + plus or ctrol + minus) the js goes haywire. This doesn't happen in other browsers. This is the real issue. Any advice on that

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  • Drag and drop an image from desktop to a web text editor (implementation in javascript)

    - by fatmatto
    I tried to write reasonably short title but i failed i guess.. Hi everybody here's what i'm trying to do: I want to implement a web text editor able to recognize when the user drag a image file over it's editing surface and it automa(gically) starts the upload and insert the image near the cursor position. In other words i don't want the user to do the usual "insert-image-browse-ok". Atm i am not very good at javascript ... i know JQuery but i have not a clear idea about how to implement this... i don't know if there's an event handler able to help me in this situation... if not then there should be i think or web apps would miss some kind of interactivity. I've heard miracles about HTML5 could it help me? I've seen such things in Google Wave but that surface doesn't seem to be a form field... google lab's black magic i guess.... Thank you in advance.

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  • Differences between matrix implementation in C

    - by tempy
    I created two 2D arrays (matrix) in C in two different ways. I don't understand the difference between the way they're represented in the memory, and the reason why I can't refer to them in the same way: scanf("%d", &intMatrix1[i][j]); //can't refer as &intMatrix1[(i * lines)+j]) scanf("%d", &intMatrix2[(i * lines)+j]); //can't refer as &intMatrix2[i][j]) What is the difference between the ways these two arrays are implemented and why do I have to refer to them differently? How do I refer to an element in each of the arrays in the same way (?????? in my printMatrix function)? int main() { int **intMatrix1; int *intMatrix2; int i, j, lines, columns; lines = 3; columns = 2; /************************* intMatrix1 ****************************/ intMatrix1 = (int **)malloc(lines * sizeof(int *)); for (i = 0; i < lines; ++i) intMatrix1[i] = (int *)malloc(columns * sizeof(int)); for (i = 0; i < lines; ++i) { for (j = 0; j < columns; ++j) { printf("Type a number for intMatrix1[%d][%d]\t", i, j); scanf("%d", &intMatrix1[i][j]); } } /************************* intMatrix2 ****************************/ intMatrix2 = (int *)malloc(lines * columns * sizeof(int)); for (i = 0; i < lines; ++i) { for (j = 0; j < columns; ++j) { printf("Type a number for intMatrix2[%d][%d]\t", i, j); scanf("%d", &intMatrix2[(i * lines)+j]); } } /************** printing intMatrix1 & intMatrix2 ****************/ printf("intMatrix1:\n\n"); printMatrix(*intMatrix1, lines, columns); printf("intMatrix2:\n\n"); printMatrix(intMatrix2, lines, columns); } /************************* printMatrix ****************************/ void printMatrix(int *ptArray, int h, int w) { int i, j; printf("Printing matrix...\n\n\n"); for (i = 0; i < h; ++i) for (j = 0; j < w; ++j) printf("array[%d][%d] ==============> %d\n, i, j, ??????); }

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  • Which Queue implementation to use in Java?

    - by devoured elysium
    I need to use a FIFO structure in my application. It needs to have at most 5 elements. I'd like to have something easy to use (I don't care for concurrency) that implements the Collection interface. I've tried the LinkedList, that seems to come from Queue, but it doesn't seem to allow me to set it's maximum capacity. It feels as if I just want at max 5 elements but try to add 20, it will just keep increasing in size to fit it. I'd like something that'd work the following way: XQueue<Integer> queue = new XQueue<Integer>(5); //where 5 is the maximum number of elements I want in my queue. for (int i = 0; i < 10; ++i) { queue.offer(i); } for (int i = 0; i < 5; ++i) { System.out.println(queue.poll()); } That'd print: 5 6 7 8 9 Thanks

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  • Implementation of APIs on diferent platforms

    - by b-gen-jack-o-neill
    OK, this is basicly just about any non-default OS API running on all different OS. But for my example let´s consider platform Windows, API SDL (Simple DirectMedia Layer). Actually this question came to my mind when I was reading about SDL. Originally, I thought that on Windows (and basicly any other OS) you must use OS API to make certain actions, like wrtiting to screen, creating window and so on, becouse that API knows what kernel calls and system subroutines calls it has to do. But when I read about SDL, I surprised me, becouse, you cannot make computer to do anything more than OS can, since you cannot acess HW directly, only thru OS API, from Console allocation to DirectX. So, my question actually is, how does this not-default-OS APIs work? Do they use (wrap) original system API (like MFC wraps win32 api)? Or, do they actually have direct acess to Windows kernel? Or is there any third, way in between? Thanks.

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  • NSDateFormatter - set device language as locale?

    - by Emil
    Hey. I'm trying to get the iPhone to display dates formatted by an NSDateFormatter in the current device language. I have tried setLocale:[NSLocale currentLocale], but that only returns 5 instead of May (or Mai, as I want it to be). Any help is appreciated. Thanks! :)

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  • Programming Language Choices for High Integrity Systems

    - by Finbarr
    What programming languages are a good choice for High Integrity Systems? An example of a bad choice is Java as there is a considerable amount of code that is inaccessible to the programmer. I am looking for examples of strongly typed, block structured languages where the programmer is responsible for 100% of the code, and there is as little interference from things like a JVM as possible. Compilers will obviously be an issue. Language must have a complete and unambiguous definition.

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  • Question regarding ideal database implementation for iPhone app

    - by Jeff
    So I have a question about the ideal setup for an app I am getting ready to build. The app is basically going to be a memorization tool and I already have an sqlite database full of content that I will be using for the app. The user will navigate through the contents of the database(using the uipickerview), and select something for memorization. If that row or cell of data is selected, it is put into a pool or a uitableview that is dedicated to showing which items you have in your "need to memorize" pool. When you go to that tableview, you can select the row, and the actual data would be populated. All information in the tableview would be deletable, in the event that they don't want it there anymore... Thats it. I know that with database interfacing, there are a few different options out there, in this particular setup, is core data the easiest approach? Is there any other way that would be better? I am just kind of looking for a point in the right direction, any help is greatly appreciated!!

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  • Is there a faster TList implementation ?

    - by dmauric.mp
    My application makes heavy use of TList, so I was wondering if there are any alternative implementations that are faster or optimized for particular use case. I know of RtlVCLOptimize.pas 2.77, which has optimized implementations of several TList methods. But I'd like to know if there is anything else out there. I also don't require it to be a TList descendant, I just need the TList functionality regardless of how it's implemented. It's entirely possible, given the rather basic functionality TList provides, that there is not much room for improvement, but would still like to verify that, hence this question.

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