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  • Dealing with state problems in functional programming

    - by Andrew Martin
    I've learned how to program primarily from an OOP standpoint (like most of us, I'm sure), but I've spent a lot of time trying to learn how to solve problems the functional way. I have a good grasp on how to solve calculational problems with FP, but when it comes to more complicated problems I always find myself reverting to needing mutable objects. For example, if I'm writing a particle simulator, I will want particle "objects" with a mutable position to update. How are inherently "stateful" problems typically solved using functional programming techniques?

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  • MySQL port 3306 blocked in csf yet can still telnet to port 3306 from external host

    - by Neek
    We have a Centos 6 VPS that was recently migrated to a new machine within the same web hosting company. It's running WHM/cPanel and has csf/lfd installed. csf is set up with mostly vanilla config. I'm no iptables expert, csf has not let me down before. If a port isn't in the TCP_IN list, it should be blocked on the firewall by iptables. My problem is that I can telnet to port 3306 from an external host, yet I think iptables ought to be blocking 3306 because of csf's rules. We are now failing a security check because of this open port. (this output is obfuscated to protect the innocent: www.ourhost.com is the host with the firewall problem) [root@nickfenwick log]# telnet www.ourhost.com 3306 Trying 158.255.45.107... Connected to www.ourhost.com. Escape character is '^]'. HHost 'nickfenwick.com' is not allowed to connect to this MySQL serverConnection closed by foreign host. So the connection is established, and MySQL refuses the connection due to its configuration. I need the network connection to be refused at the firewall level, before it reaches MySQL. Using WHM's csf web UI I can see 'Firewall Configuration' includes a fairly sensible TCP_IN line: TCP_IN: 20,21,22,25,53,80,110,143,222,443,465,587,993,995,2077,2078,2082,2083,2086,2087,2095,2096,8080 (lets ignore that I could trim that a little for now, my concern is that 3306 is not listed in that list) When csf is restarted it logs the usual slew of output as it sets up iptables rules, for example what looks like it blocking all traffic and then allowing specific ports like SSH on 22: [cut] DROP all opt -- in * out * 0.0.0.0/0 -> 0.0.0.0/0 [cut] ACCEPT tcp opt -- in !lo out * 0.0.0.0/0 -> 0.0.0.0/0 state NEW tcp dpt:22 [cut] I can see that iptables is running, service iptables status returns a long list of firewall rules. Here is my Chain INPUT section from service iptables status, hopefully that's enough to show how the firewall is configured. Table: filter Chain INPUT (policy DROP) num target prot opt source destination 1 acctboth all -- 0.0.0.0/0 0.0.0.0/0 2 ACCEPT tcp -- 217.112.88.10 0.0.0.0/0 tcp dpt:53 3 ACCEPT udp -- 217.112.88.10 0.0.0.0/0 udp dpt:53 4 ACCEPT tcp -- 217.112.88.10 0.0.0.0/0 tcp spt:53 5 ACCEPT udp -- 217.112.88.10 0.0.0.0/0 udp spt:53 6 ACCEPT tcp -- 8.8.4.4 0.0.0.0/0 tcp dpt:53 7 ACCEPT udp -- 8.8.4.4 0.0.0.0/0 udp dpt:53 8 ACCEPT tcp -- 8.8.4.4 0.0.0.0/0 tcp spt:53 9 ACCEPT udp -- 8.8.4.4 0.0.0.0/0 udp spt:53 10 ACCEPT tcp -- 8.8.8.8 0.0.0.0/0 tcp dpt:53 11 ACCEPT udp -- 8.8.8.8 0.0.0.0/0 udp dpt:53 12 ACCEPT tcp -- 8.8.8.8 0.0.0.0/0 tcp spt:53 13 ACCEPT udp -- 8.8.8.8 0.0.0.0/0 udp spt:53 14 LOCALINPUT all -- 0.0.0.0/0 0.0.0.0/0 15 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 16 INVALID tcp -- 0.0.0.0/0 0.0.0.0/0 17 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 18 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:20 19 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21 20 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22 21 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25 22 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:53 23 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80 24 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:110 25 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:143 26 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:222 27 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:443 28 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:465 29 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:587 30 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:993 31 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:995 32 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2077 33 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2078 34 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2082 35 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2083 36 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2086 37 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2087 38 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2095 39 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2096 40 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:8080 41 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:20 42 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:21 43 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:53 44 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:222 45 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:8080 46 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 8 47 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 0 48 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 11 49 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 3 50 LOGDROPIN all -- 0.0.0.0/0 0.0.0.0/0 What's the next thing to check?

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  • wbadmin incremental system state backup

    - by user74513
    I am doing system state backups on a Windows Server 2008 R2 Enterprise (Service Pack 1) machine and expected the backups after the first one to be incremental. However with each backup a new directory with vhd files are created and the vhd files are almost the same size as the with the first backup. So the backups does not seem to be incremental. I used the following command to do the backup: wbadmin start systemstatebackup -backupTarget:f: I played around with the settings under "Configure Performance Settings" in the Windows Server Backup plugin in Server Manager but according to the description at the top of the dialog these settings are not applied to system state backups. Are there any settings available for wbadmin system state backup to make the backups incremental?

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  • RESTFul: state changing actions

    - by Miro Svrtan
    I'am planning to build RESTfull API but there are some architectural questions that are creating some problems in my head. Adding backend bussiness logic to clients is option that I would like to avoid since updating multiple client platforms is hard to maintain in real time when bussiness logic can rapidly change. Lets say we have article as a resource ( api/article ), how should we implement actions like publish, unpublish,activate or deactivate and so on but to try to keep it as simple as possible? 1) Should we use api/article/{id}/{action} since a lot of backend logic can happen there like pushing to remote locations or change of multiple properties. Probably the hardest thing here is that we need to send all article data back to API for updating and multiuser work could not be implemented. For instance editor could send 5 seconds older data and overwrite fix that some other journalist just did 2 seconds ago and there is no way that I could explain to clients this since those publishing an article is really not in any way connected to updating the content. 2) Creating new resource can also be an option, api/article-{action}/id , but then returned resource would not be article-{action} but article which I'am not sure if this is proper. Also in server side code article class is handling actuall work on both resource and I'm not sure if this goes against RESTfull thinking Any suggestions are welcomed..

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  • Role of an entity state in a component based system?

    - by Paul
    Component-based entity systems are all the rage these days; everyone seems to agree they are the way to go, but no one really has a definitive implementation of such a system. I was wondering, what role do entity states (walking-left, standing, jumping, etc) have in a CBS? Do they act like controllers (i.e. they handle events and change the entity's attributes based on those events)? What about cases where a state would, for example, require that the entity enters no-clip mode? Should, that state, when it enters, maybe set the CollisionComponent of the entity to a null pointer or something? (Then, on exit, the state should restore the entity's CollisionComponent to its previous state.) Also, I guess it's the current state's job to change the entity's state to something else, right?

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  • How should I design a wizard for generating requirements and documentation

    - by user1777663
    I'm currently working in an industry where extensive documentation is required, but the apps I'm writing are all pretty much cookie cutter at a high level. What I'd like to do is build an app that asks a series of questions regarding business rules and marketing requirements to generate a requirements spec. For example, there might be a question set that asks "Does the user need to enter their age?" and a follow-up question of "What is the minimum age requirement?" If the inputs are "yes" and "18", then this app will generate requirements that look something like this: "The registration form shall include an age selector" "The registration form shall throw an error if the selected age is less than 18" Later on down the line, I'd like to extend this to do additional things like generate test cases and even code, but the idea is the same: generate some output based on rules determined by answering a set of questions. Are there any patterns I could research to better design the architecture of such an application? Is this something that I should be modeling as a finite state machine?

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  • wbadmin incremental system state backup

    - by user74513
    I am doing system state backups on a Windows Server 2008 R2 Enterprise (Service Pack 1) machine and expected the backups after the first one to be incremental. However with each backup a new directory with vhd files are created and the vhd files are almost the same size as the with the first backup. So the backups does not seem to be incremental. I used the following command to do the backup: wbadmin start systemstatebackup -backupTarget:f: I played around with the settings under "Configure Performance Settings" in the Windows Server Backup plugin in Server Manager but according to the description at the top of the dialog these settings are not applied to system state backups. Are there any settings available for wbadmin system state backup to make the backups incremental?

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  • C# Cursor stuck on busy state

    - by Ben
    So I implemented a fixed time step loop for my C# game. All it does at the moment is make a square bounce around the screen. The problem I'm having is that when I execute the program, the window doesn't allow me to close the program and the cursor is stuck on the busy icon. I have to go into visual studio and stop the program manually. Here's the loop at the moment public void run() { int updates = 0; int frames = 0; double msPerTick = 1000.0 / 60.0; double threshhold = 0; long lastTime = getCurrentTime(); long lastTimer = getCurrentTime(); while (true) { long currTime = getCurrentTime(); threshhold += (currTime - lastTime) / msPerTick; lastTime = currTime; while (threshhold >= 1) { update(); updates++; threshhold -= 1; } this.Refresh(); frames++; if ((getCurrentTime() - lastTimer) >= 1000) { this.Text = updates + " updates and " + frames + " frames per second"; updates = 0; frames = 0; lastTimer += 1000; } } }

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  • Current state of the art for holographic displays?

    - by kamziro
    In another thread I was asking about independent arcade system development, and partly it was because I'm interested in using available 3D holographic technology for the displays. I saw one which involved a rotating mirror at very high speeds, so that's probably not going to be too feasible (I'd hate to think of what happens when something goes wrong). However, I looked around for videos from trade shows, and I found this: http://www.youtube.com/watch?v=Vl0EIngM-RA But information is scarce, and I'm led to believe it's just using mirrors and reflections, and does not convey true 3D depth like the one using rotating mirrors at high speed: http://www.youtube.com/watch?v=YKCUGQ-uo8c So yeah, does anyone know if there's something better available today?

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  • session management: verifying a user's log-in state

    - by good_computer
    I am storing sessions in my database. Everytime a user logs in, I create a new row corresponding to the new session, generate a new session id and send it as a cookie to the browser. My session data looks something like this: { 'user_id': 1234 'user_name': 'Sam' ... } When a request comes, I check whether a cookie with a session id is sent. If it is, I fetch session data from my database (or memcache) corresponding to that session id. When the user logs out, I remove the session data from my database (and memcache), and delete the cookie from the user's browser too. Notice that in my session data, I don't have something like logged_in: true. This is because if I find a session record in the database (or memcache) I deduce that the user is logged in, and if there is no session record found, the user is not logged in. My question is: is this the right approach? Should I have a logged_in key in my session data? Is there any possibility that a session record may be present on the server where the corresponding user is actually NOT logged in? Are there any security implications in having or not having such a key?

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  • Game state management (Game, Menu, Titlescreen, etc)

    - by munchor
    Basically, in every single game I've made so far, I always have a variable like "current_state", which can be "game", "titlescreen", "gameoverscreen", etc. And then on my Update function I have a huge: if current_state == "game" game stuf ... else if current_state == "titlescreen" ... However, I don't feel like this is a professional/clean way of handling states. Any ideas on how to do this in a better way? Or is this the standard way?

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  • How bad is it to have two methods with the same name but different signatures in two classes?

    - by Super User
    I have a design problem related to a public interface, the names of methods, and the understanding of my API and code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class has one public method named collision, and the second has one private method called _collision. The two methods differs in argument type and number. As an example let's say that _collision checks if the object is colliding with another object with certain conditions l, r, t, b (collide on the left side, right side, etc) and returns true or false. The public collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think it's better to avoid overloading the design with different names for methods that do almost the same thing, but in distinct contexts and classes. Is this clear enough to the reader or I should change the method's name?

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  • How bad it's have two methods with the same name but differents signatures in two classes?

    - by Super User
    I have a design problem relationated with the public interface, the names of methods and the understanding of my API and my code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class have one public method named collision and the second have one private method called _collision. The two methods differs in arguments type and number. In the API _m method is private. For the example let's say that the _collision method checks if the object is colliding with another_ object with certain conditions l, r, t, b (for example, collide the left side, the right side, etc) and returns true or false according to the case. The collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think is better avoid overload the design with different names for methods who do almost the same think, but in distinct contexts and classes. This is clear enough to the reader or I should change the method's name?

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  • Game State / Screen Management

    - by Ashylnn Mac
    What's the best way to handle game states / screens? My problem is this: PlayGameScreen adds a new InventoryGameScreen to the game during it's update. This immediately adds InventoryGameScreen to the array of GameScreens. That's throwing an exception when iterating over the array that the contents of the array have changed. Should I have two more arrays, like screensToBeAdded and screensToBeRemoved and do all the processing for them at the end of the game loop after drawing all the other screens?

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  • How to change the state of a singleton in runtime

    - by user34401
    Consider I am going to write a simple file based logger AppLogger to be used in my apps, ideally it should be a singleton so I can call it via public class AppLogger { public static String file = ".."; public void logToFile() { // Write to file } public static log(String s) { AppLogger.getInstance().logToFile(s); } } And to use it AppLogger::log("This is a log statement"); The problem is, what is the best time I should provide the value of file since it is a just a singleton? Or how to refactor the above code (or skip using singleton) so I can customize the log file path? (Assume I don't need to write to multiple at the same time) p.s. I know I can use library e.g. log4j, but consider it is just a design question, how to refactor the code above?

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  • State variables in VIM

    - by dotancohen
    Is there any way to have a state variable in VIM? Consider: " Relative line numbers in Normal mode, absolute in Insert mode. Ctrl-N to toggle set relativenumber autocmd InsertEnter * :set number autocmd InsertLeave * :set relativenumber inoremap <C-n> <C-o>:call NumberToggle()<cr> nnoremap <C-n> :call NumberToggle()<cr> function! NumberToggle() if(useRelNums != 1) let useRelNums=1 set number else let useRelNums=0 set relativenumber endif endfunc Of course, useRelNums is undefined. I would like to keep this variable defined between calls to the NumberToogle() function, i.e. a state variable. How is this done? I'm sure that I could repurpose some other VIM variable as a workaround (such as the state of paste for a bad example) but I would prefer a real solution. Thanks.

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