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  • Are Multiple Iterators possible in php?

    - by artvolk
    Good day! I know that C# allows multiple iterators using yield, like described here: http://stackoverflow.com/questions/1754041/is-multiple-iterators-is-possible-in-c In PHP there is and Iterator interface. Is it possible to implement more than one iteration scenario for a class? More details (EDIT): For example I have class TreeNode implementing single tree node. The whole tree can be expressed using only one this class. I want to provide iterators for iterating all direct and indirect children of current node, for example using BreadthFirst or DepthFirst order. I can implement this Iterators as separate classes but doing so I need that tree node should expose it's children collection as public. C# pseudocode: public class TreeNode<T> { ... public IEnumerable<T> DepthFirstEnumerator { get { // Some tree traversal using 'yield return' } } public IEnumerable<T> BreadthFirstEnumerator { get { // Some tree traversal using 'yield return' } } }

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  • Aren't Information Expert / Tell Don't Ask at odds with Single Responsibility Principle?

    - by moffdub
    It is probably just me, which is why I'm asking the question. Information Expert, Tell Don't Ask, and SRP are often mentioned together as best practices. But I think they are at odds. Here is what I'm talking about: Code that favors SRP but violates Tell Don't Ask, Info Expert: Customer bob = ...; // TransferObjectFactory has to use Customer's accessors to do its work, // violates Tell Don't Ask CustomerDTO dto = TransferObjectFactory.createFrom(bob); Code that favors Tell Don't Ask / Info Expert but violates SRP: Customer bob = ...; // Now Customer is doing more than just representing the domain concept of Customer, // violates SRP CustomerDTO dto = bob.toDTO(); If they are indeed at odds, that's a vindication of my OCD. Otherwise, please fill me in on how these practices can co-exist peacefully. Thank you. Edit: someone wants a definition of the terms - Information Expert: objects that have the data needed for the operation should host the operation Tell Don't Ask: don't ask objects for data in order to do work; tell the objects to do the work Single Responsibility Principle: each object should have a narrowly defined responsibility

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  • How to make this OO?

    - by John
    Hello, Sorry for the poor title,I'm new to OOP so I don't know what is the term for what I need to do. I have, say, 10 different Objects that inherit one Object.They have different amount and type of class members,but all of them have one property in common - Visible. type TObj1=class(TObject) private a:integer; ...(More members) Visible:Boolean; end; TObj2=class(TObject) private b:String; ...(More members) Visible:Boolean; end; ...(Other 8 objects) For each of them I have a variable. var Obj1:TObj1; Obj2:TObj2; Obj3:TObj3; ....(Other 7 objects) Rule 1: Only one object can be initialized at a time(others have to be freed) to be visible. For this rule I have a global variable var CurrentVisibleObj:TObject; //Because they all inherit TObject Finally there is a procedure that changes visibility. procedure ChangeObjVisibility(newObj:TObject); begin CurrentVisibleObj.Free; //Free the old object CurrentVisibleObj:=newObj; //assign the new object CurrentVisibleObj:= ??? //Create new object CurrentVisibleObj.Visible:=true; //Set visibility to new object end; There is my problem,I don't know how to initialize it,because the derived class is unknown. How do I do this? I simplified the explanation,in the project there are TFrames each having different controls and I have to set visible/not visible the same way(By leaving only one frame initialized). Sorry again for the title,I'm very new to OOP.

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  • How to Manage project in this scenario

    - by vijay.shad
    Hi All, I am working on a web application which has got good amount of static or pre-login pages. These pages can have some simple forms as well where we would like to capture the visitor's details. Post login, I have got my main application. I am confused about the development and deployment architecture of my application. Post login part of my application has a release cycle of 1-2 months while pre-login pages are to be updated on a weekly basis. It is difficult to make a release of pre-login pages as the overall war also contains post-login application & which sometimes is not release ready. Currently, I have got both these parts bundled in the single war project. Please help me by letting me know the best practices whereby I can achieve following: Manage the releases of these two parts independently. I am using Maven. So is there a way I can share the resources, such as CSS, images etc between these two parts. Header and footer of my application is going to be same on pre-login & post-login pages. I was thinking of deploying these apps as two war files in my tomcat container. But then how will I manage the common resources like Css, images etc. Rgds Vijay

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  • adding one time options to items

    - by rap-uvic
    Hello, I'm building an Event Registration site. For any given event, we'll have a handful of items to choose from. I have a table for these items. For each event we might have special options for users. For example, for one of the events new users get to buy an item which is not available to other users. This may not apply to all the events. For other events we might have some other restriction on items. I will obviously be checking this programmatically on application side. I would like to though, set up a column containing flag in the items table. But I don't find it feasible because this condition may only apply to one particular event. I don't want all the future items to have this column. What is a good approach to take in such a situation? Should I create a special "restrictions" table and just do a join? How would I handle this on the application side?

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  • Why eGet() in EMF returns Object rather than EObject?

    - by Gabriel Šcerbák
    I am working on some code using the EMF framework in Java, but it is really hard to use, e.g. I cannot implement OCL-like query API on top of EMF which would be type-safe. One of the reasons is that eGet() for a EStructuralFeature return just an Object, not EObject. So anything I would write must use much of null checking, type checking and type casting which is unsafe, not performant and cannot be generalized in a reusable way. Why doesn't EMF generate dummy implementations with EObject wrappers for arbitrary Object value? Implementing the EObject and hence the EClass interfaces even with simple throw UnsupportedOperationException is really a pain (the APIs are too big). The same holds for the eContainer() method which makes navigatinng the model upwards painful.

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  • Algorithm for max integer in an array of integers

    - by gagneet
    Explain which algorithm you would use to implement a function that takes an array of integers and returns the maximum integer in the collection, assuming that the length of the array is less than 1000. Would you use Bubble Sort or Merge Sort and Why? Also, what happens to the above algorithm choice, if the array length is greater than 1000?

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  • document.getElementById not working in IE

    - by Alloi
    Hi, I am using the below js code in order to change the class when a link is clicked. document.getElementById("gifts").setAttribute("class", "gkvSprite selected"); This is not working in IE but it does in FF and Chrome Then I changed the code to : document.getElementById("gifts").setAttribute("className", "gkvSprite selected"); Then it worked in IE stopped working in FF and Chrome. Could someone please help me out here? Thanks in Advance Alloi

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  • Testing system where App-level and Request-level IoC containers exist

    - by Bobby
    My team is in the process of developing a system where we're using Unity as our IoC container; and to provide NHibernate ISessions (Units of work) over each HTTP Request, we're using Unity's ChildContainer feature to create a child container for each request, and sticking the ISession in there. We arrived at this approach after trying others (including defining per-request lifetimes in the container, but there are issues there) and are now trying to decide on a unit testing strategy. Right now, the application-level container itself is living in the HttpApplication, and the Request container lives in the HttpContext.Current. Obviously, neither exist during testing. The pain increases when we decided to use Service Location from our Domain layer, to "lazily" resolve dependencies from the container. So now we have more components wanting to talk to the container. We are also using MSTest, which presents some concurrency dilemmas during testing as well. So we're wondering, what do the bright folks out there in the SO community do to tackle this predicament? How does one setup an application that, during "real" runtime, relies on HTTP objects to hold the containers, but during test has the flexibility to build-up and tear-down the containers consistently, and have the ServiceLocation bits get to those precise containers. I hope the question is clear, thanks!

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  • In .NET, Why Can I Access Private Members of a Class Instance within the Class?

    - by AMissico
    While cleaning some code today written by someone else, I changed the access modifier from Public to Private on a class variable/member/field. I expected a long list of compiler errors that I use to "refactor/rework/review" the code that used this variable. Imagine my surprise when I didn't get any errors. After reviewing, it turns out that another instance of the Class can access the private members of another instance declared within the Class. Totally unexcepted. Is this normal? I been coding in .NET since the beginning and never ran into this issue, nor read about it. I may have stumbled onto it before, but only "vaguely noticed" and move on. Can anyone explain this behavoir to me? I would like to know the "why" I can do this. Please explain, don't just tell me the rule. Am I doing something wrong? I found this behavior in both C# and VB.NET. The code seems to take advantage of the ability to access private variables. Sincerely, Totally Confused Class Jack Private _int As Integer End Class Class Foo Public Property Value() As Integer Get Return _int End Get Set(ByVal value As Integer) _int = value * 2 End Set End Property Private _int As Integer Private _foo As Foo Private _jack As Jack Private _fred As Fred Public Sub SetPrivate() _foo = New Foo _foo.Value = 4 'what you would expect to do because _int is private _foo._int = 3 'TOTALLY UNEXPECTED _jack = New Jack '_jack._int = 3 'expected compile error _fred = New Fred '_fred._int = 3 'expected compile error End Sub Private Class Fred Private _int As Integer End Class End Class

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  • Evenly select N elems from array

    - by ninuhadida
    Hi, I need to evenly select n elements from an array. I guess the best way to explain is by example. say I have: array [0,1,2,3,4] and I need to select 3 numbers.. 0,3,4. of course, if the array length <= n, I just need to return the whole array. I'm pretty sure there's a defined algorithm for this, been trying to search, and I took a look at Introduction to algorithms but couldn't find anything that met my needs (probably overlooked it) The problem I'm having is that I can't figure out a way to scale this up to any array [ p..q ], selecting N evenly elements. note: I can't just select the even elements from the example above.. A couple other examples; array[0,1,2,3,4,5,6], 3 elements ; I need to get 0,3,6 array[0,1,2,3,4,5], 3 elements ; I need to get 0, either 2 or 3, and 5

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  • Reasons to start a new project in COBOL

    - by luvieere
    Are there any feasible reasons to start a new project in COBOL? What benefits of this language one would find convincing enough to start a new project in it? I'm thinking more about viewing the language in terms of Behavior Driven Development, something related to the steps involved in using a framework such as Cucumber, only that behavior description and step definition would be integrated into one unit by using tha language's features.

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  • Teradata equivalent of persisted computed column (in SQL Server)

    - by Cade Roux
    We have a few tables with persisted computed columns in SQL Server. Is there an equivalent of this in Teradata? And, if so, what is the syntax and are there any limitations? The particular computed columns I am looking at conform some account numbers by removing leading zeros - an index is also created on this conformed account number: ACCT_NUM_std AS ISNULL(CONVERT(varchar(39), SUBSTRING(LTRIM(RTRIM([ACCT_NUM])), PATINDEX('%[^0]%', LTRIM(RTRIM([ACCT_NUM])) + '.' ), LEN(LTRIM(RTRIM([ACCT_NUM]))) ) ), '' ) PERSISTED With the Teradata TRIM function, the trimming part would be a little simpler: ACCT_NUM_std AS COALESCE(CAST(TRIM(LEADING '0' FROM TRIM(BOTH FROM ACCT_NUM))) AS varchar(39)), '' ) I guess I could just make this a normal column and put the code to standardize the account numbers in all the processes which insert into the table. We did this to put the standardization code in one place.

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  • Perl vs Python but with more style than normally

    - by user350571
    I'm learning perl and everytime I search for perl stuff in the internet I get some random page with people saying that perl should die because code written in it looks like a lesson in steganography. Then they say that python is clean and stuff like that. Now, I know that those comparisons are always stupid and made by fellows that feel that languages are a extension of their boring personality so, let me ask instead: can you give me the implementation of a widely known algorithm to deal with a data structure like red-black trees in both languages so I can compare?

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  • Best Fit Scheduling Algorithim

    - by Teegijee
    I'm writing a scheduling program with a difficult programming problem. There are several events, each with multiple meeting times. I need to find an arrangement of meeting times such that each schedule contains any given event exactly once, using one of each event's multiple meeting times. Obviously I could use brute force, but that's rarely the best solution. I'm guessing this is a relatively basic computer science problem, which I'll learn about once I am able to start taking computer science classes. In the meantime, I'd prefer any links where I could read up on this, or even just a name I could Google.

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  • Algorithm to determine which points should be visible on a map based on zoom

    - by lgratian
    Hi! I'm making a Google Maps-like application for a course at my Uni (not something complex, it should load the map of a city for example, not the whole world). The map can have many layers, including markers (restaurants, hospitals, etc.) The problem is that when you have many points and you zoom out the map it doesn't look right. At this zoom level only some points need to be visible (and at the maximum map size, all points). The question is: how can you determine which points should be visible for a specified zoom level? Because I have implemented a PR Quadtree to speed up rendering I thought that I could define some "high-priority" markers (that are always visible, defined in the map editor) and put them in a queue. At each step a marker is removed from the queue and all it's neighbors that are at least D units away (D depends on the zoom levels) are chosen and inserted in the queue, and so on. Is there any better way than the algorithm I thought of? Thanks in advance!

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  • Builder pattern and singletons

    - by Berryl
    Does anyone have any links to some code they like that shows a good example of this in c#? As an example of bad code, here is what a builder I have now looks like. I'm trying to have a way to keep the flexibility of the builder pattern but not rebuild the properties. Cheers, Berryl public abstract class ActivityBuilder { public abstract ActivityBuilder Build(); public bool IsBuilt { get; protected set; } public IEnumerable<Project> Projects { get { if(_projects==null) { Build(); } return _projects; } } protected IEnumerable<Project> _projects; // .. other properties }

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  • Idiom vs. pattern

    - by Roger Pate
    In the context of programming, how do idioms differ from patterns? I use the terms interchangeably and normally follow the most popular way I've heard something called, or the way it was called most recently in the current conversation, e.g. "the copy-swap idiom" and "singleton pattern". The best difference I can come up with is code which is meant to be copied almost literally is more often called pattern while code meant to be taken less literally is more often called idiom, but such isn't even always true. This doesn't seem to be more than a stylistic or buzzword difference. Does that match your perception of how the terms are used? Is there a semantic difference?

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  • Producer/consumer in Grails?

    - by Mulone
    Hi all, I'm trying to implement a Consumer/Producer app in Grails, after several unsuccessful attempts at implementing concurrent threads. Basically I want to store all the events coming from a clients (through separate AJAX calls) in a single queue and then process such a queue in a linear way as soon as new events are added. This looks like a Producer/Consumer problem: http://en.wikipedia.org/wiki/Producer-consumer_problem How can I implement this in Grails (maybe with a timer or even better by generating an event 'process queue')? Basically I'd like to a have a singleton service waiting for new events in the queue and processing them linearly (even if the queue is loaded by several concurrent processes). Any hints? Cheers!

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  • Flex: Push the Button

    - by Rachel
    For what real time scenarios/use cases one should go to Flex Technology ? What real time problems you have solved using Flex Technology ? What real time problems have you faced because of using Flex Technology and what was your work around for that use case ?

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  • best practices - multiple functions vs single function with switch case

    - by Amit
    I have a situation where I need to perform several small (but similar) tasks. I can think of two ways to achieve this. First Approach: function doTask1(); function doTask2(); function doTask3(); function doTask4(); Second Approach: // TASK1, TASK2, ... TASK4 are all constants function doTask(TASK) { switch(TASK) { case TASK1: // do task1 break; case TASK2: // do task2 break; case TASK3: // do task3 break; case TASK4: // do task4 break; } } A few more tasks may be added in future (though the chances are rare. but this cannot be ruled out) Please suggest which of the two approaches (or if any other) is a best practice in such a situation.

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