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  • How to void checked exceptions in Java?

    - by deamon
    I consider checked exception for a design mistake in the Java language. They lead to leaky abstractions and a lot of clutter in the code. It seems that they force the programmer to handle exceptions early although they are in most cases better handled lately. So my question is how to avoid checked exception? My idea is to execute the actual code inside an exception translator using lambda expressions. Example: ExceptionConverter.convertToRuntimeException(() => { // do things that could throw checked exceptions here }); If for example a IOException occurs it gets rethrown as an exception with the same name but from a different class hierarchy (based on RuntimeException). This approach would effectivly remove the need to handle or declare checked exceptions. Exceptions could then be handled where and if it makes sense. Another solution would be to declare IOException throws Exception on each method. What do you think which solution is better? Do you know any better approach to avoid (suppress) checked exceptions in Java?

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  • Does semi-normalization exist as a concept? Is it "normalized"?

    - by Gracchus
    If you don't mind, a tldr on my experience: My experience tldr I have an application that's heavily dependent upon uncertainty, a bane to database design. I tried to normalize it as best as I could according to the capabilities of my database of choice, but a "simple" query took 50ms to read. Nosql appeals to me, but I can't trust myself with it, and besides, normalization has cut down my debugging time immensely over and over. Instead of 100% normalization, I made semi-redundant 1:1 tables with very wide primary keys and equivalent foreign keys. Read times dropped to a few ms, and write times barely degraded. The semi-normalized point Given this reality, that anyone who's tried to rely upon views of fully normalized data is aware of, is this concept codified? Is it as simple as having wide unique and foreign keys, or are there any hidden secrets to this technique? Or is uncertainty merely a special case that has extremely limited application and can be left on the ash heap?

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  • What are basic programming directions? [closed]

    - by Goward Gerald
    What are basic programming directions? Can you please list them and give a brief review of each? Would be nice to have a list for each direction (web-development/*enterprise*/standalone/*mobile*/etc, correct me if I skipped something) like this: 1). Most popular languages of this direction (php for web, objective C for iOS mobile development etc) 2). It's demand on market (from 0 to 5, subjective) 3). How much tasks differ (do you always create same-of-a-kind programs which are like clones of each oother or projects change and you often get to create something interesting, new and fresh?) 4). Freelance demand (from 0 to 5) 5). Fun factor (from 0 to 5, totally subjective but still write it please) Thanks!

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  • Fast set indexing data structure for superset retrieval

    - by Asterios
    I am given a set of sets: {{a,b}, {a,b,c}, {a,c}, {a,c,f}} I would like to have a data structure to index those sets such that the following "lookup" is executed fast: find all supersets of a given set. For example, given the set {a,c} the structure would return {{a,b,c}, {a,c,f}, {a,c}} but not {a,b}. Any suggestions? Could this be done with a smart trie-like data structure storing sets after a proper sorting? This data structures is going to be queried a lot. Thus, I'm searching for a structure that might be expensive in build but rather fast to query.

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  • Why don't we just fix Javascript?

    - by Jan Meyer
    Javascript sucks because of a few fatalities well pointed out by Douglas Crockford. We talk a lot about it. But the point here is, why we don't fix it? Coffeescript of course does that and a lot more. But the question here is another: if we provide a webservice that can convert one version of Javascript to the next, and so on, we can keep the language up to date. Such a conversion allows old code to run, albeit with an ever-increasing startup delay, as newer browsers convert old code to the new syntax. To avoid that delay, the site only needs to take the output of the code-transform and paste it in! The effort has immediate benefits for those businesses interested in the results. The rest can sleep tight: their code will continue to run. If we provide backward code-transformation also, then elder browsers can also run ANY new code! Migration scripts should be created by those that make changes to a language. Today they don't, which is in itself a fundamental omission! It should be am obvious part of their job to provide them, as their job isn't really done without them. The onus of making it work should be on them. With this system Any site will be able to run in Any browser, but new code will run best on the newest browsers. This way we reap the benefit of an up-to-date and productive development environment, where today we suffer, supposedly because of yesterday. This is a misconception. We are all trapped in committee-thinking, and we drag along things that only worsen our performance over time! We cause an ever increasing complexity that is hard to underestimate. Javascript is easily fixed. The fact is we don't. As an example, I have seen Patrick Michaud tackle the migration problem in PmWiki. It included forward migration scripts. Whenever syntax changes were made, a migration script was added to transform pages to the new syntax. As far as I know, ALL migrations have worked flawlessly. In other words, we don't tackle the migration problem, we just drag it along. We are incompetent! And why is that? Because technically incompetent people feel they must decide for us. Because they are incompetent, fear rules them. They are obnoxiously conservative, and we suffer the consequence of bad leadership. But the competent don't need to play by the same rules. They can (and must) change them. They are the path forward. It is about time to leave the past behind, and pursue the leanest meanest, no, eternal functionality. That would in and of itself revolutionize programming. So, why don't we stop whining and fix programming? Begin with Javascript and change the world. Even if the browser doesn't hook into this system, coders could. So language updaters should take it upon them to provide migration scripts. Once they exist, browsers may take advantage of them.

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  • How would you gather client's data on Google App Engine without using Datastore/Backend Instances too much?

    - by ruslan
    I'm relatively new to StackExchange and not sure if it's appropriate place to ask design question. Site gives me a hint "The question you're asking appears subjective and is likely to be closed". Please let me know. Anyway.. One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting? Thank you very much in advance for your thoughts.

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  • Is it typical for a provider of a web services to also provide client libraries?

    - by HDave
    My company is building a corporate Java web-app and we are leaning towards using GWT-RPC as the client-server protocol for performance reasons. However, in the future, we will need to provide an API for other enterprise systems to access our data as well. For this, we were thinking of a SOAP based web service. In my experience it is common for commercial providers of enterprise web applications to provide client libraries (Java, .NET, C#, etc.). Is this generally the case? I ask because if so, then why bother using SOAP or REST or any standard web services protocol at all? Why not just create a client libraries that communicate via GWT-RPC?

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  • What tools, libraries, or framework is needed to create a completely offline Javascript application?

    - by makerofthings7
    I am interested in creating a HTML application that can run as disconnected from the server as possible. Two examples of this include OWA in Exchange 2013 and to a lesser extent and the client available at www.ripple.com With the focus on OWA in Exchange 2013, what is needed to replicate the offline functionality available in a different application? A list technologies, frameworks, etc would be immensely helpful

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  • Using Sql Server Change Data Capture with a frequently changing schema

    - by Pete
    We are looking into enabling Sql Server Change Data Capture for a new subsystem we are building. It's not really because we need it, but we are being pushed for having a complete history traceability, and CDC would nicely solve this requirement with minimum effort on our parts. We are following an agile development process, which in this case means that we frequently make changes to the database schema, e.g. adding new columns, moving data to other columns, etc. We did a small test where we created a table, enabled CDC for that table, and then added a new column to the table. Changes to the new column is not registered in the CDC table. Is there a mechanism to update the CDC table to the new schema, and are there any best practices to how you deal with captured data when migrating the database schema?

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  • What is a good GUI text editor with code folding on Linux

    - by quanticle
    When I'm on Linux, I usually program using either gvim or emacs (depending on the language I'm working in, and the configuration of the machine). However, one thing I miss from the Windows world is code folding. Editors like Notepad++ and IDEs like Visual Studio allow shrink, or fold, blocks of code into single line headings. Are there any Linux editors with this facility? I know Eclipse can do code folding, but I don't want to launch Eclipse just to edit a HTML file.

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  • MVC Validation with ModelState.isValid through a wizard

    - by Emmanuel TOPE
    I'm working on a small educational project on MVC 3, and I'm facing a small problem, when attempting to handle validation in my application through a wizard. I tried to get benefit from the ability of MVC3 to deliver content of a different view using the same URL, when handling an [HttpPost] method on a page. I my case,my main model's class contains about ten [Required] properties, that I would like to expose through a small wizard in 3 steps , So I want that the user may be able to enter his personal informations in the first step, then respond to some questions in the second stepp and finally receive a confirmation mail from the web application whit his credentials in the last step. I can't access the last step, because of the ModelState.isValid method that I use to handle validations, and which can't perform properly if I define some properties as [Required], but don't put them on the first view. As the replies to those questions remain in a couple of choices, I've thinked that I may use some nullable bool? for in order to avoid validation issues, but know that it's not the proper way. Are there someone who would like to help me find a way to extend my validation to those three steps ? Thanks in advance and sorry for my english, I'm not a native speaker.

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  • Architecture- Tracking lead origin when data is submitted by a server

    - by Kevin
    I'm looking for some assistance in determining the least complex strategy for tracking leads on an affiliate's website. The idea is to make the affiliate's integration with my application as easy as possible. I've run into theoretical barriers, so i'm here to explore other options. Application Overview: This is a lead aggregation / distribution platform. We will be focusing on the affiliate portion of this website. Essentially affiliates sign up, enter in marketing campaigns and sell us their conversions. Problem to be solved: We want to track a lead's origin and other events on the affiliate site. We want to know what pages, ads, and forms they viewed before they converted. This can easily be solved with pixel tracking. Very straightforward. Theoretical Issues: I thought I would ask affiliates to place the pixel where I could log impressions and set a third party cookie when the pixel is first called. Then I could associate future impressions with this cookie. The problem is that when the visitor converts on the affiliate's site and I receive their information via HTTP POST from the Affiliate's server I wouldn't be able to access the cookie and associate it with the lead record unless the lead lands on my processor via a redirect and is then redirected back to the affiliate's landing page. I don't want to force the affiliates to submit their forms directly to my tracking site, so allowing them to make an HTTP POST from their server side form processor would be ideal. I've considered writing JavaScript to set a First Party cookie but this seems to make things more complicated for the affiliate. I also considered having the affiliate submit the lead's data via a conversion pixel. This seems to be the most ideal scenario so far as almost all pixels are as easy as copy/paste. The only complication comes from the conversion pixel- which would submit all of the lead information and the request would come from the visitor's machine so I could access my third party cookie.

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  • Why is testing MVC Views frowned upon?

    - by Peter Bernier
    I'm currently setting the groundwork for an ASP.Net MVC application and I'm looking into what sort of unit-tests I should be prepared to write. I've seen in multiple places people essentially saying 'don't bother testing your views, there's no logic and it's trivial and will be covered by an integration test'. I don't understand how this has become the accepted wisdom. Integration tests serve an entirely different purpose than unit tests. If I break something, I don't want to know a half-hour later when my integration tests break, I want to know immediately. Sample Scenario : Lets say we're dealing with a standard CRUD app with a Customer entity. The customer has a name and an address. At each level of testing, I want to verify that the Customer retrieval logic gets both the name and the address properly. To unit-test the repository, I write an integration test to hit the database. To unit-test the business rules, I mock out the repository, feed the business rules appropriate data, and verify my expected results are returned. What I'd like to do : To unit-test the UI, I mock out the business rules, setup my expected customer instance, render the view, and verify that the view contains the appropriate values for the instance I specified. What I'm stuck doing : To unit-test the repository, I write an integration test, setup an appropriate login, create the required data in the database, open a browser, navigate to the customer, and verify the resulting page contains the appropriate values for the instance I specified. I realize that there is overlap between the two scenarios discussed above, but the key difference it time and effort required to setup and execute the tests. If I (or another dev) removes the address field from the view, I don't want to wait for the integration test to discover this. I want is discovered and flagged in a unit-test that gets multiple times daily. I get the feeling that I'm just not grasping some key concept. Can someone explain why wanting immediate test feedback on the validity of an MVC view is a bad thing? (or if not bad, then not the expected way to get said feedback)

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  • Suggestions for connecting .NET WPF GUI with Java SE Server aoo

    - by Sam Goldberg
    BACKGROUND We are building a Java (SE) trading application which will be monitoring market data and sending trade messages based on the market data, and also on user defined configuration parameters. We are planning to provide the user with a thin client, built in .NET (WPF) for managing the parameters, controlling the server behavior, and viewing the current state of the trading. The client doesn't need real-time updates; it will instead update the view once every few seconds (or whatever interval is configured by the user). The client has about 6 different operations it needs to perform with the server, for example: CRUD with configuration parameters query subset of the data receive updates of current positions from server It is possible that most of the different operations (except for receiving data) are just different flavors of managing the configuration parameters, but it's too early in our analysis for us to be sure. To connect the client with the server, we have been considering using: SOAP Web Service RESTful service building a custom TCP/IP based API (text or xml) (least preferred - but we use this approach with other applications we have) As best as I understand, pros and cons of the different web service flavors are: SOAP pro: totally automated in .NET (and Java), modifying server side interface require no code changes in communication layer, just running refresh on Web Service reference to regenerate the classes. con: more overhead in the communication layer sending more text, etc. We're not using J2EE container so maybe doesn't work so well with J2SE REST pro: lighter weight, less data. Has good .NET and Java support. (I don't have any real experience with this, so don't know what other benefits it has.) con: client will not be automatically aware if there are any new operations or properties added (?), so communication layer needs to be updated by developer if server interface changes. con: (both approaches) Server cannot really push updates to the client at regular intervals (?) (However, we won't mind if client polls the server to get updates.) QUESTION What are your opinions on the above options or suggestions for other ways to connect the 2 parts? (Ideally, we don't want to put much work into the communication layer, because it's not the significant part of the application so the more off-the-shelf and automated the better.)

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  • Extreme Programming Dying? [closed]

    - by jonny
    Is Extreme Programming Dying? I've been reviewing my fellow students reports on extreme programming.(I am a student myself) Some students are claiming that extreme programming lacks in empirical evidences, and is relevantly new, hence lacking in empirical evidence. XP is already 13 years old it should be considered as new, from my perspective. I guess the practices of XP has been tweaked and used in newer methodologies such as scrum. What are your point of view on this, do you guys think XP is Dying?

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  • Do I really need to learn Python? [closed]

    - by Pouya
    These days, I see the name "Python" a lot. Mostly when I'm doing some programming on linux/mac, I see a trace of Python. I have a fair knowledge of C++ and I'm quite good at Java. I also know Delphi which comes handy sometimes. I've been good with these languages, however, I was wondering if learning Python could make it better. What does it offer that makes it worth learning? What are its key/unique advantages/features?

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  • How does one pronounce "cron" as in "cron job"?

    - by Rooke
    Before someone ban-hammers this question as they do with all other pronunciation questions, let me explain its relevance. Verbal communication among co-workers and partners is important; today I was on a conference call with people discussing what I thought was something to do with "Chrome", as in Google Chrome. I pronounce the "cron" in "cron job" with a short O, much like "tron", "gone," or "pawn", but this individual pronouced it with a long O, as in "hone", "bone", or "stone" (notice the e at the end of all those!). Is there a standard pronunciation? Or is this a matter of opinion. For example, there's nothing ambiguous about the pronunciation of "Firefox", but debate is raging over "potato" and "tomato".

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  • How Did we get from CLI to Graphics?

    - by Nathaniel Bennett
    I'm confused when looking into graphics - specifically with operating systems. I mean, how can a computer render a CLI/console along with a GUI. GUI's are completely different from Text. and How Can we have GUI windows that Display Text interfaces, ie how can we have CLI in modern Graphics Operating system - that's what I'm mainly trying to grip on to. How Do Graphic's get rendered to display? is there some sort of memory address that a GPU access which holds all pixel data, and there system's within OS's that Gather the pixel position of Windows and Widgets, along with the Z Index and rasterize them to that memory address, which then the GPU loads to the screen? How About the CLI's integrated with Graphics? how does the OS Tell the GPU that a certain part of the screen wants to display text while the rest, whats to display pixel data? it's all very confusing. Shed some light in it, will ya?

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  • Handling "related" work within a single agile work item

    - by Tesserex
    I'm on a project team of 4 devs, myself included. We've been having a long discussion on how to handle extra work that comes up in the course of a single work item. This extra work is usually things that are slightly related to the task, but not always necessary to accomplish the goal of the item (that may be an opinion). Examples include but are not limited to: refactoring of the code changed by the work item refactoring code neighboring the code changed by the item re-architecting the larger code area around the ticket. For example if an item has you changing a single function, you realize the entire class now could be redone to better accommodate this change. improving the UI on a form you just modified When this extra work is small we don't mind. The problem is when this extra work causes a substantial extension of the item beyond the original feature point estimation. Sometimes a 5 point item will actually take 13 points of time. In one case we had a 13 point item that in retrospect could have been 80 points or more. There are two options going around in our discussion for how to handle this. We can accept the extra work in the same work item, and write it off as a mis-estimation. Arguments for this have included: We plan for "padding" at the end of the sprint to account for this sort of thing. Always leave the code in better shape than you found it. Don't check in half-assed work. If we leave refactoring for later, it's hard to schedule and may never get done. You are in the best mental "context" to handle this work now, since you're waist deep in the code already. Better to get it out of the way now and be more efficient than to lose that context when you come back later. We draw a line for the current work item, and say that the extra work goes into a separate ticket. Arguments include: Having a separate ticket allows for a new estimation, so we aren't lying to ourselves about how many points things really are, or having to admit that all of our estimations are terrible. The sprint "padding" is meant for unexpected technical challenges that are direct barriers to completing the ticket requirements. It is not intended for side items that are just "nice-to-haves". If you want to schedule refactoring, just put it at the top of the backlog. There is no way for us to properly account for this stuff in an estimation, since it seems somewhat arbitrary when it comes up. A code reviewer might say "those UI controls (which you actually didn't modify in this work item) are a bit confusing, can you fix that too?" which is like an hour, but they might say "Well if this control now inherits from the same base class as the others, why don't you move all of this (hundreds of lines of) code into the base and rewire all this stuff, the cascading changes, etc.?" And that takes a week. It "contaminates the crime scene" by adding unrelated work into the ticket, making our original feature point estimates meaningless. In some cases, the extra work postpones a check-in, causing blocking between devs. Some of us are now saying that we should decide some cut off, like if the additional stuff is less than 2 FP, it goes in the same ticket, if it's more, make it a new ticket. Since we're only a few months into using Agile, what's the opinion of all the more seasoned Agile veterans around here on how to handle this?

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  • Naming a predicate: "precondition" or "precondition_is_met"?

    - by RexE
    In my web app framework, each page can have a precondition that needs to be satisfied before it can be displayed to the user. For example, if user 1 and user 2 are playing a back-and-forth role-playing game, user 2 needs to wait for user 1 to finish his turn before he can take his turn. Otherwise, the user is displayed a waiting page. This is implemented with a predicate: def precondition(self): return user_1.completed_turn The simplest name for this API is precondition, but this leads to code like if precondition(): ..., which is not really obvious. Seems to me like it is more accurate to call it precondition_is_met(), but not sure about that either. Is there a best practice for naming methods like this?

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  • How Microsoft Market DotNet?

    - by Fendy
    I just read an Joel's article about Microsoft's breaking change (non-backwards compatibility) with dot net's introduction. It is interesting and explicitly reflected the condition during that time. But now almost 10 years has passed. The breaking change It is mainly on how bad is Microsoft introducing non-backwards compatibility development tools, such as dot net, instead of improving the already-widely used asp classic or VB6. As much have known, dot net is not natively embedded in windows XP (yes in vista or 7), so in order to use the .net apps, you need to install the .net framework of over 300mb (it's big that day). However, as we see that nowadays many business use .net as their main development tools, with asp.net or mvc as their web-based applications. C# nowadays be one of tops programming languages (the most questions in stackoverflow). The more interesing part is, win32api still alive even there is newer technology out there (and still widely used). Imagine if microsoft does not introduce the breaking change, there will many corporates still uses asp classic or vb-based applications (there still is, but not that much). There are many corporates use additional services such as azure or sharepoint (beside how expensive is it). Please note that I also know there are many flagships applications (maybe adobe's and blizzard's) still use C-based or older language and not porting to newer high-level language. The question How can Microsoft persuade the users to migrate their old applications into dot net? As we have known it is very hard and give no immediate value when rewrite the applications (netscape story), and it is very risky. I am more interested in Microsoft's way and not opinion such as "because dot net is OOP, or dot net is dll-embedable, etc". This question may be constructive, as the technology is vastly changes over times lately. As we can see, Microsoft changes Asp.Net webform to MVC, winform is legacy now, it is starting to change to use windows store rather than basic-installment, touchscreen and later on we will have see-through applications such as google class. And that will be breaking changes. We will need to account portability as an issue nowadays. We will need other than just mere technology choice, but also migration plans. Even maybe as critical as we might need multiplatform language compiler, as approached by Joel's Wasabi. (hey, I read his articles too much!)

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  • Why is there a "new" in Go?

    - by dystroy
    I'm still puzzled as why we have new in Go. When you want to instantiate a struct, you do t := Thing{} and, obviously, you can get a pointer to a new instance by doing t := &Thing{} But there's also this possibility : t := new(Thing) This last one seems a little alien to me. &Thing{} is as clear and concise as new(Thing) and it uses only constructs you often use elsewhere. It's also more extensible as you might change it to &Thing{3} or &Thing{Feets:7}. In my opinion, having a supplementary keyword is costly, it makes the language more complex and adds to what you must know. And it might mask to newcomers what's behind instantiating a struct. It also makes one more reserved word. So what's the reasoning behind new ? Is it something useful ? Should we use it ?

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  • Pros and cons of hosted scripts

    - by P.Brian.Mackey
    I have seen some developers use hosted scripts to link their libraries. cdn.jquerytools.org is one example. I have also seen people complain that a hosted script link has been hijacked. How safe is using hosted scripts in reality? Are the scripts automatically updated? For example, if jQuery 5 goes to 6 do I automatically get version 6 or do I need to update my link? I also see that Google has a large set of these scripts setup for hosting. What are the pros and cons?

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  • How often do CPUs make calculation errors?

    - by veryfoolish
    In Dijkstra's Notes on Structured Programming he talks a lot about the provability of computer programs as abstract entities. As a corollary, he remarks how testing isn't enough. E.g., he points out the fact that it would be impossible to test a multiplication function f(x,y) = x*y for any large values of x and y across the entire ranges of x and y. My question concerns his misc. remarks on "lousy hardware". I know the essay was written in the 1970s when computer hardware was less reliable, but computers still aren't perfect, so they must make calculation mistakes sometimes. Does anybody know how often this happens or if there are any statistics on this?

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  • How do we keep dependent data structures up to date?

    - by Geo
    Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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