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• Actor based concurrency and cancellation

  - by Akash

  I'm reading about actor based concurrency and I appreciate the simplicity of actors sequentially processing messages on a single thread. However there is one scenario that doesn't seen possible. Suppose that actor A sends a message to actor B, who then performs some long running task and returns a completion message to actor A. How can actor A force actor B to cancel the long running task after it has started? If actor B is running the task in its message queue thread, it won't pick up the cancellation message until it had completed the task; if actor B runs the task in a background thread then it seems to be violating the principle of actors. Is there a common way that this scenario is handled with actors? Or does each actor language/framework take a different approach? Or is this not a suitable problem to tackle via actors?

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• What triggered the popularity of lambda functions in modern mainstream programming languages?

  - by Giorgio

  In the last few years anonymous functions (AKA lambda functions) have become a very popular language construct and almost every major / mainstream programming language has introduced them or is planned to introduce them in an upcoming revision of the standard. Yet, anonymous functions are a very old and very well-known concept in Mathematics and Computer Science (invented by the mathematician Alonzo Church around 1936, and used by the Lisp programming language since 1958, see e.g. here). So why didn't today's mainstream programming languages (many of which originated 15 to 20 years ago) support lambda functions from the very beginning and only introduced them later? And what triggered the massive adoption of anonymous functions in the last few years? Is there some specific event, new requirement or programming technique that started this phenomenon? IMPORTANT NOTE The focus of this question is the introduction of anonymous functions in modern, main-stream (and therefore, maybe with a few exceptions, non functional) languages. Also, note that anonymous functions (blocks) are present in Smalltalk, which is not a functional language, and that normal named functions have been present even in procedural languages like C and Pascal for a long time. Please do not overgeneralize your answers by speaking about "the adoption of the functional paradigm and its benefits", because this is not the topic of the question.

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• How do I grok NHibernate's QueryOver API?

  - by Brant Bobby

  I've run into the limits of what NHibernate 3.0's LINQ provider is capable of and decided it's time to learn about one of the more powerful (or at least feature-complete) options: the QueryOver API. The problem is, I have zero experience with ICriteria, and all of the tutorials I've been able to find online either: Assume I'm an ICriteria expert and simply show me how to convert ICriteria code to the new fluent interface, or Are trivial "here's how you do an inner join" examples that don't really help me understand more complex concepts like projections, subqueries, requirements, or whatever other magic the API is capable of. What should I read to really learn about QueryOver, and how to make full use of it?

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• Class hierarchy problem in this social network model

  - by Gerenuk

  I'm trying to design a class system for a social network data model - basically a link/object system. Now I have roughly the following structure (simplified and only relevant methods shown) class Data: "used to handle the data with mongodb" "can link, unlink data and also return other linked data" "is basically a proxy object that only stores _id and accesses mongodb on requests" "it looks like {_id: ..., _out: [id1, id2,...], _inc: [id3, id4, ...]}" def get_node(self, id) "create a new Data object from the underlying mongodb" "each data object can potentially create a reference object to new mongo data" "this is needed when the data returns the linked objects" class Node: """ this class proxies linking calls to .data it includes additional network logic operations whereas Data only contains a basic database solution """ def __init__(self, data): "the infrastructure realization is stored as composition by an included object data" "Node bascially proxies most calls to the infrastructure object data" def get_node(self, data): "creates a new object of class Object or Link depending on data" class Object(Node): "can have multiple connections to Link" class Link(Node): "has one 'in' and one 'out' connection to an Object" This system is working, however maybe wouldn't work outside Python. Note that after reading links Now I have two questions here: 1) I want to infrastructure of the data storage to be replacable. Earlier I had Data as a superclass of Node so that it provided the neccessary calls. But (without dirty Python tricks) you cannot replace the superclass dynamically. Is using composition therefore recommended? The drawback is that I have to proxy most calls (link, unlink etc). Any thoughts? 2) The class Node contains the common method .get_node which is used to built new Object or Link instances after reading out the data. Some attribute of data decided whether the object which is only stored by id should be instantiated as an Object or Link class. The problem here is that Node needs to know about Object and Link in advance, which seems dodgy. Do you see a different solution? Both Object and Link need to instantiate one of all possible types depending on what the find in their linked data. Are there any other ideas how to implement a flexible Object/Link structure where the underlying database storage is isolated?

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• How do you handle measuring Code Coverage in JavaScript

  - by Dancrumb

  In order to measure Code Coverage for JavaScript unit tests, one needs to instrument the code, run the tests and then perform post-processing. My concern is that, as a result, you are unit testing code that will never be run in production. Since JavaScript isn't compiled, what you test should be precisely what you execute. So here's my question, how do you handle this? One thought I had was to run Unit Testing on the production code and use that for my pass fail. I would then create a shadow of my production code, with instrumentation and run my unit tests again; this would give me my code coverage stats. Has anyone come across a method that is a little more graceful than this?

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• How many copies are needed to enlarge an array?

  - by user10326

  I am reading an analysis on dynamic arrays (from the Skiena's algorithm manual). I.e. when we have an array structure and each time we are out of space we allocate a new array of double the size of the original. It describes the waste that occurs when the array has to be resized. It says that (n/2)+1 through n will be moved at most once or not at all. This is clear. Then by describing that half the elements move once, a quarter of the elements twice, and so on, the total number of movements M is given by: This seems to me that it adds more copies than actually happen. E.g. if we have the following: array of 1 element +--+ |a | +--+ double the array (2 elements) +--++--+ |a ||b | +--++--+ double the array (4 elements) +--++--++--++--+ |a ||b ||c ||c | +--++--++--++--+ double the array (8 elements) +--++--++--++--++--++--++--++--+ |a ||b ||c ||c ||x ||x ||x ||x | +--++--++--++--++--++--++--++--+ double the array (16 elements) +--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--+ |a ||b ||c ||c ||x ||x ||x ||x || || || || || || || || | +--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--+ We have the x element copied 4 times, c element copied 4 times, b element copied 4 times and a element copied 5 times so total is 4+4+4+5 = 17 copies/movements. But according to formula we should have 1*(16/2)+2*(16/4)+3*(16/8)+4*(16/16)= 8+8+6+4=26 copies of elements for the enlargement of the array to 16 elements. Is this some mistake or the aim of the formula is to provide a rough upper limit approximation? Or am I missunderstanding something here?

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• Many small scripts, one repository or multiple?

  - by The Jug

  A co-worker and myself have run into an issue that we have multiple opinions on. Currently we have a git repository that we are keeping all of our cronjobs in. There are about 20 crons and they are not really related except for the fact that they are all small python scripts and essential for some activity. We are using a fabric.py file to deploy and a requirements.txt file to manage requirements for all of the scripts. Our issue is basically, do we keep all of these scripts in one git repository or should we be separating them out into their own repositories? By keeping them in one repository it is easier to deploy them onto one server. We can use just one cron file for all the scripts. However this feels wrong, as the 20 cronjobs are not logically related. Additionally, when using one requirements.txt file for all the scripts, it's hard to figure out what the dependencies are for a particular script and they all have to use the same versions of packages. We could separate all of the scripts out into their own repositories but this creates 20 different repositories that need to be remembered and dealt with. Most of these scripts are not very large and that solution seems to be overkill. A related question is, do we use one big crontab file for all cronjobs, or a separate file for each? If each has their own, how does one crontab's installation avoid overwriting the other 19? This also seems like a pain as there would then by 20 different cron files to keep track of. In short, our main question and issue is do we keep them all closely bundled as one repository or do we separate them out into their own repository with their own requirements.txt and fabfile.py? We feel like we're also probably looking over some really simple solution. Is there an easier way to deal with this issue?

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• How to get better at solving Dynamic programming problems

  - by newbie

  I recently came across this question: "You are given a boolean expression consisting of a string of the symbols 'true', 'false', 'and', 'or', and 'xor'. Count the number of ways to parenthesize the expression such that it will evaluate to true. For example, there is only 1 way to parenthesize 'true and false xor true' such that it evaluates to true." I knew it is a dynamic programming problem so i tried to come up with a solution on my own which is as follows. Suppose we have a expression as A.B.C.....D where '.' represents any of the operations and, or, xor and the capital letters represent true or false. Lets say the number of ways for this expression of size K to produce a true is N. when a new boolean value E is added to this expression there are 2 ways to parenthesize this new expression 1. ((A.B.C.....D).E) ie. with all possible parenthesizations of A.B.C.....D we add E at the end. 2. (A.B.C.(D.E)) ie. evaluate D.E first and then find the number of ways this expression of size K can produce true. suppose T[K] is the number of ways the expression with size K produces true then T[k]=val1+val2+val3 where val1,val2,val3 are calculated as follows. 1)when E is grouped with D. i)It does not change the value of D ii)it inverses the value of D in the first case val1=T[K]=N.( As this reduces to the initial A.B.C....D expression ). In the second case re-evaluate dp[K] with value of D reversed and that is val1. 2)when E is grouped with the whole expression. //val2 contains the number of 'true' E will produce with expressions which gave 'true' among all parenthesized instances of A.B.C.......D i) if true.E = true then val2 = N ii) if true.E = false then val2 = 0 //val3 contains the number of 'true' E will produce with expressions which gave 'false' among all parenthesized instances of A.B.C.......D iii) if false.E=true then val3=( 2^(K-2) - N ) = M ie. number of ways the expression with size K produces a false [ 2^(K-2) is the number of ways to parenthesize an expression of size K ]. iv) if false.E=false then val3 = 0 This is the basic idea i had in mind but when i checked for its solution http://people.csail.mit.edu/bdean/6.046/dp/dp_9.swf the approach there was completely different. Can someone tell me what am I doing wrong and how can i get better at solving DP so that I can come up with solutions like the one given above myself. Thanks in advance.

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• Calling COM from Intel Fortran?

  - by user57460

  I'm trying to get COM working from my Fortran application. I do a "COMINITIALIZE" followed by a "COMCreateObjectByProgID". Both of these appear to be successful and return a status of zero. However, when I try to use the COM object, I get "Unhandled exception at 0x00000000 in FortranProg01.exe: 0xC0000005: Access violation." I realize that this error can mean almost anything, but has anyone got some suggestions of common problems with COM that produce this problem? Here are some more details. My program code: program FortranProg01 use myolepg implicit none integer*4 comInitStatus integer:: comCreateStatus INTEGER(INT_PTR_KIND()) $OBJECT INTEGER(4) funcResult REAL(8) pkgVersion call COMINITIALIZE(comInitStatus) print *, comInitStatus call COMCreateObjectByProgID('MyOlePg.MyOlePkg', $OBJECT, comCreateStatus) print *, comCreateStatus funcResult = IMyOlePkg_GetPackageVersion($OBJECT, pkgVersion) print *, funcResult call COMUNINITIALIZE() end program FortranProg01 The wizard-generated interface code: INTERFACE !property PackageVersion INTEGER(4) FUNCTION IMyOlePkg_GetPackageVersion($OBJECT, pVal) INTEGER(INT_PTR_KIND()), INTENT(IN) :: $OBJECT ! Object Pointer !DEC$ ATTRIBUTES VALUE :: $OBJECT REAL(8), INTENT(OUT) :: pVal !DEC$ ATTRIBUTES REFERENCE :: pVal !DEC$ ATTRIBUTES STDCALL :: IMyOlePkg_GetPackageVersion END FUNCTION IMyOlePkg_GetPackageVersion END INTERFACE Any help would be much appreciated! Thanks! Brad.

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• How to pick a great working team?

  - by Javierfdr

  I've just finished my master and I'm starting to dig into the laboral world, i.e. learning how programming teams and technology companies work in the real world. I'm starting to design the idea of my own service or product based on free software, and I will require a well coupled, enthusiast and fluid team to build and the idea. My problem is that I'm not sure which would be the best skills to ask for a programming team of 4-5 members. I have many friends and acquaintances, with whom I've worked during my studies. Must of those ones I have in mind are very capable and smart people, with a good logic and programming base, although some of them have some characteristics that I believe that could influtiate negatively in the group: lack of communication, fear to debate ideas, hard to give when debating, lack of structured programming (testing, good commenting, previous design and analysis). Some of them have this negative characteristics, but must of them have a lot of enthusiasm, nice working skills (from an individual point of view), and ability to see the whole picture. The question is: how to pick the best team for a large scale project, with a lot of programming? Which of these negative skills do you think are just too influential? Which can be softened with good leadership? Wich good skills are to be expected? And any other opinion about social and programming skills of a programming team.

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• How do I know when should I package my classes in Ruby?

  - by Omega

  In Ruby, I'm creating a small game development framework. Just some personal project - a very small group of friends helping. Now I am in need of handling geometric concepts. Rectangles, Circles, Polygons, Vectors, Lines, etc. So I made a class for each of these. I'm stuck deciding whether I should package such classes in a module, such as Geometry. So I'd access them like Geometry::Rectangle, or just Rectangle if I include the module. Now then, my question isn't about this specific scenario. I'd like to know, when is it suitable to package similar classes into one module in Ruby? What factors should I consider? Amount of classes? Usage frequency? Complexity?

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• Rule of thumb for cost vs. savings for code re-use

  - by Styler

  Is it a good rule of thumb to always write code for the intent of re-using it somewhere down the road? Or, depending on the size of the component you are writing, is it better practice to design it for re-use when it makes sense with regards to time spent on it. What is a good rule of thumb for spending extra time on analysis and design on project components that have "some probability" of being needed later down the road for other things that may or may need this part. For example, if I have the need for project X to do things A, and B. A definitely needs to be written for re-use because it just makes sense to do so. B is very project specific at the moment, and I can hack it all together in a couple days to finish the project on time and give everyone kudos for being a great team, etc. Or if we say, lets spend a whole friggin' 2 weeks figuring out what project Y/Z might need this thing for and spend a load of extra time on on part B because someday we might need to use it on project Y/Z (where the savings will be realized). I'd imagine a perfect world situation would be a nicely crafted combination of project specific vs. re-use architected components given the project. However some code shops might feel it would be a great idea to write everything for the intention of using it at some point down the road.

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• How easy is it to alter a browser fingerprint?

  - by JFig

  I am researching this question for a possible paper. Given the exploitation of user identities for risk management and market tracking, how easy is it to alter a browser enough to throw off fingerprinting techniques? My current sources are the EFF Panopticlick project- https://www.eff.org/deeplinks/2010/01/primer-information-theory-and-privacy and Peter Eckersly's follow-up presentation at Def Con 18- http://privacy-pc.com/articles/how-safe-is-your-browser-peter-ackersley-on-personally-identifiable-information-basics.html

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• What is the precise definition of programming paradigm?

  - by Kazark

  Wikipedia defines programming paradigm thus: a fundamental style of computer programming which is echoed in the descriptive text of the paradigms tag on this site. I find this a disappointing definition. Anyone who knows the words programming and paradigm could do about that well without knowing anything else about it. There are many styles of computer programming at many level of abstraction; within any given programming paradigm, multiple styles are possible. For example, Bob Martin says in Clean Code (13), Consider this book a description of the Object Mentor School of Clean Code. The techniques and teachings within are the way that we practice our art. We are willing to claim that if you follow these teachings, you will enjoy the benefits that we have enjoyed, and you will learn to write code that is clean and professional. But don't make the mistake of thinking that we are somehow "right" in any absolute sense. Thus Bob Martin is not claiming to have the correct style of Object-Oriented programming, even though he, if anyone, might have some claim to doing so. But even within his school of programming, we might have different styles of formatting the code (K&R, etc). There are many styles of programming at many levels. So how can we define programming paradigm rigorously, to distinguish it from other categories of programming styles? Fundamental is somewhat helpful, but not specific. How can we define the phrase in a way that will communicate more than the separate meanings of each of the two words—in other words, how can we define it in a way that will provide additional meaning for someone who speaks English but isn't familiar with a variety of paradigms?

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• Simple Architecture Verification

  - by Jean Carlos Suárez Marranzini

  I just made an architecture for an application with the function of scoring, saving and loading tennis games. The architecture has 2 kinds of elements: components & layers. Components: Standalone elements that can be consumed by other components or by layers. They might also consume functionality from the model/bottom layer. Layers: Software components whose functionality rests on previous layers (except for the model layer). -Layers: -Models: Data and it's behavior. -Controllers: A layer that allows interaction between the views and the models. -Views: The presentation layer for interacting with the user. -Components: -Persistence: Makes sure the game data can be stored away for later retrieval. -Time Machine: Records changes in the game through time so it's possible to navigate the game back and forth. -Settings: Contains the settings that determine how some of the game logic will apply. -Game Engine: Contains all the game logic, which it applies to the game data to determine the path the game should take. This is an image of the architecture (I don't have enough rep to post images): http://i49.tinypic.com/35lt5a9.png The requierements which this architecture should satisfy are the following: Save & load games. Move through game history and see how the scoreboard changes as the game evolves. Tie-breaks must be properly managed. Games must be classified by hit-type. Every point can be modified. Match name and player names must be stored. Game logic must be configurable by the user. I would really appreciate any kind of advice or comments on this architecture. To see if it is well built and makes sense as a whole. I took the idea from this link. http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller

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• Which is more important in a web application code promotion hierarchy? production environment to repo equivalence or unidirectional propagation?

  - by ghbarratt

  Lets say you have a code promotion hierarchy consisting of several environments, (the polar end) two of which are development (dev) and production (prod). Lets say you also have a web application where important (but not developer controlled) files are created (and perhaps altered) in the production environment. Lets say that you (or someone above you) decided that the files which are controlled/created/altered/deleted in the production environment needed to go into the repository. Which of the following two sets of practice / approaches do you find best: Committing these non-developed file modifications made in the production environment so that the repository reflects the production environment as closely and as often as possible. Generally ignoring the non-developed production environment alterations, placing confidence in backups to restore the production environment should it be harmed, and keeping a resolution to avoid pushing developments through the promotion hierarchy in the reverse direction (avoiding pushing from prod to dev), only committing the files found in the production environment if they were absolutely necessary in other environments for development. So, 1 or 2, and why? PS - I am currently slightly biased toward maintaining production environment to repository equivalence (option 1), but I keep an open mind and would accept an answer supporting either.

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• Can an object oriented program be seen as a Finite State Machine?

  - by Peretz

  This might be a philosophical/fundamental question, but I just want to clarify it. In my understanding a Finite State Machine is a way of modeling a system in which the system's output will not only depend on the current inputs, but also the current state of the system. Additionally, as the name suggests it, a finite state machine can be segmented in a finite N number of states with its respective state and behavior. If this is correct, shouldn't every single object with data and function members be a state in our object oriented model, making any object oriented design a finite state machine? If that is not the interpretation of a FSM in object design, what exactly people mean when they implement a FSM in software? am I missing something? Thanks

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• Code review process when using GIT as a repository?

  - by Sid

  What is the best process for code review when using GIT? Current process: We have a GIT server with a master branch to which everyone commits Devs work off the local master mirror or a local feature branch Devs commit to server's master branch Devs request code review on last commit Problem: Any bug in code review are already in master by the time it's caught. Worse, usually someone has burnt a few hours trying to figure out what happened... So, we would like To do code review BEFORE delivery into the 'master'. Have a process that works with a global team (no over the shoulder reviews!) something that doesn't require an individual dev to be at his desk/machine to be powered up so someone else can remote in (remove human dependency, devs go home at different timezones) We use TortoiseGIT for a visual representation of a list of files changed, diff'ing files etc. Some of us drop into a GIT shell when the GUI isn't enough, but ideally we'd like the workflow to be simple and GUI based (I want the tool to lift any burden, not my devs).

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• How can I use UML to model a relationship between two classes, where one has functions exposed as friend to the other?

  - by user1796528

  I have a two classes: ------------ --------------- X Y ------------ --------------- relation ------------ ------------------ --------------- A() C() B() D() E() ------------ --------------- I want to inherit just these two functions from X class, where they are defined with the friend access modifier. My class will be: --------------- Y --------------- --------------- C() A() D() --------------- Y class uses some functions of X class namely A and D. How can I model this relationship in a UML class diagram?

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• On what basis would you split donation money among your open source team members without any strife?

  - by Vigneshwaran

  I am a developer of an open source project which is hosted in SourceForge. It started out as a little app then after some releases, it got more and more popular and it started consuming more time and responsibility from me. So I have enabled the donation option in SourceForge. I'm passionate to continue developing it for free but if (ever) any money comes in, how should I split it with my team? Should I split the amount equally among the number of team members? (50-50 as it is two-member team now) Number of classes, commits or any other valuable submissions by team members? Any other idea? What would you do in such situation? Please give your opinions. I hope this question will be useful for others.

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• Delivery terminology and order of magnitude

  - by Peter Turner

  What is the standard way of describing how software products are released and the proportionate order of magnitude to which the changes relative to the software product are conveyed? Is Release Update Patch Bug Fix redundant? or Is Update Patch too terse? As an end user I'd think that all bug fixes are patches (insofar as they are not 100% new code) and all patches should be updates (insofar as they don't degrade the product) and all updates should be releases (insofar as they are actually released), but this really doesn't help anyone understand why they need to get them. Then, if the person who makes the software change appends "critical" or "zero-day" in the notes, I would be unwise to leave the changes unapplied.

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• Why does F. Wagner consider "NOT (AI_LARGER_THAN_8.1)" to be ambiguous?

  - by oosterwal

  In his article on Virtual Environments (a part of his VFSM specification method) Ferdinand Wagner describes some new ways of thinking about Boolean Algebra as a software design tool. On page 4 of this PDF article, when describing operators in his system he says this: Control statements need Boolean values. Hence, the names must be used to produce Boolean results. To achieve this we want to combine them together using Boolean operators. There is nothing wrong with usage of AND and OR operators with their Boolean meaning. For instance, we may write: DI_ON OR AI_LARGER_THAN_8.1 AND TIMER_OVER to express the control situation: digital input is on or analog input is larger than 8.1 and timer is over. We cannot use the NOT operator, because the result of the Boolean negation makes sense only for true Boolean values. The result of, for instance, NOT (AI_LARGER_THAN_8.1) would be ambiguous. If "AI_LARGER_THAN_8.1" is acceptable, why would he consider "NOT (AI_LARGER_THAN_8.1)" to be ambiguous?

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• How long was Microsoft working on .NET before they released it?

  - by Richard DesLonde

  With the whole CLI, CTS, CLS, etc., not only did they release a powerful platform/infrastructure, but they released all the specs that describe it etc. It supports potentially infinite myriad languages, platforms, etc. This seems like an insane amount of work, even for a behemoth like Microsoft - especially since it turns out they did a damn good job. How long were they working on this before releasing it (.NET 1.0)?

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• How does one pluralize <see cref="Notation">'s?

  - by Jordan

  What is the most appropriate way of writing this comment: /// <summary> /// Order - Identifies the ordinal location of this category /// relative to other listed categories. /// </summary> if I'm wanting to wrap "category" in <see> tags? I've considered: /// <summary> /// Order - Identifies the ordinal location of this <see cref="Category"/> /// relative to other listed <see cref="Category"/>'s. /// </summary> Do you see my dilemma? Edit: I should add that I am using Visual Studio's XML Comments. So I am somewhat restricted as to the schema. I believe cref has to point to a valid type reference.

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• Mail Scanning System

  - by Mr D

  In the same way gmail can generate ads based on email content, I am looking for a way to develop a system which can: Allow users to connect their email address to our site It then would continously monitor all incomming emails From the incomming emails there would be a critera(e.g. a certain address or subject) if any of the emails matched the critea it would would be saved to a database Then once a new email had been found the users would receive an email notification will tells them to log back into the site to see it. My questions are: Would this be possible? What would be a good language to use(generally I like php, python and java) Are there any frameworks which would help do this? How would I connect the users email account to allow access to their emails(do I need a mail server?) Any advice? Thank you! If you need more information please let me know.

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