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  • Rails 3 - yield return or callback won't call in view <%= yield(:sidebar) || render('shared/sidebar'

    - by rzar
    Hey folks, I'm migrating a Website from Rails 2 (latest) to Rails 3 (beta2). Testing with Ruby 1.9.1p378 and Ruby 1.9.2dev (2010-04-05 trunk 27225) Stuck in a situation, i don't know which part will work well. Suspect yield is the problem, but don't know exactly. In my Layout Files I use the following technique quite often: app/views/layouts/application.html.erb: <%= yield(:sidebar) || render('shared/sidebar') %> For Example the partial look like: app/views/shared/_sidebar.html.erb: <p>Default sidebar Content. Bla Bla</p> Now it is time for the key part! In any view, I want to create a content_for block (optional). This can contain a pice of HTML etc. example below. If this block is set, the pice HTML inside should render in application.html.erb. If not, Rails should render the Partial at shared/_sidebar.html.erb on the right hand side. app/views/books/index.html.erb: <% content_for :sidebar do %> <strong>You have to read REWORK, a book from 37signals!</strong> <% end %> So you've got the idea. Hopefully. This technique worked well in any Rails 2.x Application. Now, in Rails 3 (beta2) only the yield Part is working. || render('shared/sidebar') The or side will not process by rails or maybe ruby. Thanks for input and time!

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  • What do you think of this generator syntax?

    - by ChaosPandion
    I've been working on an ECMAScript dialect for quite some time now and have reached a point where I am comfortable adding new language features. I would love to hear some thoughts and suggestions on the syntax. Example generator { yield 1; yield 2; yield 3; if (true) { yield break; } yield continue generator { yield 4; yield 5; yield 6; }; } Syntax GeneratorExpression:     generator  {  GeneratorBody  } GeneratorBody:     GeneratorStatementsopt GeneratorStatements:     StatementListopt GeneratorStatement GeneratorStatementsopt GeneratorStatement:     YieldStatement     YieldBreakStatement     YieldContinueStatement YieldStatement:     yield  Expression  ; YieldBreakStatement:     yield  break  ; YieldContinueStatement:     yield  continue  Expression  ; Semantics The YieldBreakStatement allows you to end iteration early. This helps avoid deeply indented code. You'll be able to write something like this: generator { yield something1(); if (condition1 && condition2) yield break; yield something2(); if (condition3 && condition4) yield break; yield something3(); } instead of: generator { yield something1(); if (!condition1 && !condition2) { yield something2(); if (!condition3 && !condition4) { yield something3(); } } } The YieldContinueStatement allows you to combine generators: function generateNumbers(start) { return generator { yield 1 + start; yield 2 + start; yield 3 + start; if (start < 100) { yield continue generateNumbers(start + 1); } }; }

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  • C# yield in nested method

    - by Fastidious
    If I step through the following code the call to ReturnOne() is skipped. static IEnumerable<int> OneThroughFive() { ReturnOne(); yield return 2; yield return 3; yield return 4; yield return 5; } static IEnumerator<int> ReturnOne() { yield return 1; } I can only assume that the compiler is stripping it out because what I'm doing is not valid. I'd like the ability to isolate my enumeration into various methods. Is this possible?

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  • putting <%=yield %> in a partial for ajax jquery calls

    - by odpogn
    I'm trying to make the "home" link in my <%= render 'layouts/header' %> do an ajax/jquery call to change the <%= yield %> in a partial inside my content div. all i get are blanks in the view.. <%= yield %> works fine when put in a partial without ajax, but it doesn't display anything when using ajax... can yield not be used this way? all I'm really looking for is the ability to click on my sites navigation links without having to reload the entire page... my application.html.erb file looks like so: <head> $(function() { $("#home").live("click", function() { $.get(this.href, null, null, "script"); return false; }); }); </head> <body> <div id="container"> <%= render 'layouts/header' %> <div id="content"> <%= render 'layouts/content' %> </div> <%= render 'layouts/footer' %> </div> </body> my <%= render 'layouts/header' %> contains: <%= link_to "Home", root_path, :id => "home" %> my <%= render 'layouts/content' %> only contains: <%= yield %> home.js.erb $("#content").html("<%= escape_javascript(render("layouts/content")) %>");

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  • Attribute lost with yield

    - by Nelson
    Here's an interesting one... There is some code that I'm trying to convert from IList to IEnumerable: [Something(123)] public IEnumerable<Foo> GetAllFoos() { SetupSomething(); DataReader dr = RunSomething(); while (dr.Read()) { yield return Factory.Create(dr); } } The problem is, SetupSomething() comes from the base class and uses: Attribute.GetCustomAttribute(new StackTrace().GetFrame(1).GetMethod(), typeof(Something)) Yield ends up creating MoveNext(), MoveNext() calls SetupSomething(), and MoveNext() does not have the [Something(123)] attribute. I can't change the base class, so it appears I am forced to stay with IList or implement IEnumerable manually (and add the attribute to MoveNext()). Is there any other way to make yield work in this scenario?

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  • Problem with debug watch in Visual Studio with yield return enumerator methods

    - by Stuart
    I have a method which returns an IEnumerable<> which it builds up using the yield return syntax: public IEnumerable<ValidationError> Validate(User user) { if (String.IsNullOrEmpty(user.Name)) { yield return new ValidationError("Name", ValidationErrorType.Required); } [...] yield break; } If I put a breakpoint in the method, I can step over each line, but if I try to use the Watch or Immediate windows to view the value of a variable I get this error: Cannot access a non-static member of outer type '[class name].Validate' via nested type '[class name]' Does anyone know why this is and how I can get around it?

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  • implementing a state machine using the "yield" keyword

    - by Matt Warren
    Is it feasible to use the yield keyword to implement a simple state machine as shown here. To me it looks like the C# compiler has done the hard work for you as it internally implements a state machine to make the yield statement work. Can you piggy-back on top of the work the compiler is already doing and get it to implement most of the state machine for you? Has anyone done this, is it technically possible?

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  • scala for yield setting a value

    - by coubeatczech
    Hi, I want to create a list of GridBagPanel.Constraints. I read it in the scala programming book, that there is a cool for-yield construction, but I probably haven't understood the way it works correctly, because my code doesn't compile. Here it is: val d = for { i <- 0 until 4 j <- 0 until 4 } yield { c = new Constraints c.gridx = j c.gridy = i } I want to generate a List[Constraints] and for every constraint set different x,y values so later, when I later add the components, they're going to be in a grid.

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  • Multithreading, when to yield versus sleep

    - by aaa
    hello. To clarify terminology, yield is when thread gives up its time slice. My platform of interest is POSIX threads, but I think question is general. Suppose I have consumer/producer pattern. If I want to throttle either consumer or producer, which is better to use, sleep or yield? I am mostly interested in efficiency of using either function. Thanks

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  • When should I use Yield in c#?

    - by Steve
    I have a vage understanding of the Yield keyword in c#, but I haven't yet seen the need to use it in my code. This probably comes from a lack of understanding of it.. So; What are some typical good usages of Yield?

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  • using yield in C# like I would in Ruby

    - by Sarah Vessels
    Besides just using yield for iterators in Ruby, I also use it to pass control briefly back to the caller before resuming control in the called method. What I want to do in C# is similar. In a test class, I want to get a connection instance, create another variable instance that uses that connection, then pass the variable to the calling method so it can be fiddled with. I then want control to return to the called method so that the connection can be disposed. I guess I'm wanting a block/closure like in Ruby. Here's the general idea: private static MyThing getThing() { using (var connection = new Connection()) { yield return new MyThing(connection); } } [TestMethod] public void MyTest1() { // call getThing(), use yielded MyThing, control returns to getThing() // for disposal } [TestMethod] public void MyTest2() { // call getThing(), use yielded MyThing, control returns to getThing() // for disposal } ... This doesn't work in C#; ReSharper tells me that the body of getThing cannot be an iterator block because MyThing is not an iterator interface type. That's definitely true, but I don't want to iterate through some list. I'm guessing I shouldn't use yield if I'm not working with iterators. Any idea how I can achieve this block/closure thing in C# so I don't have to wrap my code in MyTest1, MyTest2, ... with the code in getThing()'s body?

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  • C# yield return not returning an item as expected

    - by Jiho Han
    I have following code: private void ProcessQueue() { foreach (MessageQueueItem item in GetNextQueuedItem()) PerformAction(item); } private IEnumerable<MessageQueueItem> GetNextQueuedItem() { if (_messageQueue.Count > 0) yield return _messageQueue.Dequeue(); } Initially there is one item in the queue as ProcessQueue is called. During PerformAction, I would add more items to _messageQueue. However, the foreach loop quits after the initial item and does not see the subsequent items added. I sense that somehow the initial state of the queue is being captured by yield. Can someone explain what is happening and give a solution?

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  • Yield only as many are required from a generator

    - by Matt Joiner
    I wish to yield from a generator only as many items are required. In the following code a, b, c = itertools.count() I receive this exception: ValueError: too many values to unpack I've seen several related questions, however I have zero interest in the remaining items from the generator, I only wish to receive as many as I ask for, without providing that quantity in advance. It seems to me that Python determines the number of items you want, but then proceeds to try to read and store more than that number. How can I yield only as many items as I require, without passing in how many items I want?

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  • yield – Just yet another sexy c# keyword?

    - by George Mamaladze
    yield (see NSDN c# reference) operator came I guess with .NET 2.0 and I my feeling is that it’s not as wide used as it could (or should) be.   I am not going to talk here about necessarity and advantages of using iterator pattern when accessing custom sequences (just google it).   Let’s look at it from the clean code point of view. Let's see if it really helps us to keep our code understandable, reusable and testable.   Let’s say we want to iterate a tree and do something with it’s nodes, for instance calculate a sum of their values. So the most elegant way would be to build a recursive method performing a classic depth traversal returning the sum.           private int CalculateTreeSum(Node top)         {             int sumOfChildNodes = 0;             foreach (Node childNode in top.ChildNodes)             {                 sumOfChildNodes += CalculateTreeSum(childNode);             }             return top.Value + sumOfChildNodes;         }     “Do One Thing” Nevertheless it violates one of the most important rules “Do One Thing”. Our  method CalculateTreeSum does two things at the same time. It travels inside the tree and performs some computation – in this case calculates sum. Doing two things in one method is definitely a bad thing because of several reasons: ·          Understandability: Readability / refactoring ·          Reuseability: when overriding - no chance to override computation without copying iteration code and vice versa. ·          Testability: you are not able to test computation without constructing the tree and you are not able to test correctness of tree iteration.   I want to spend some more words on this last issue. How do you test the method CalculateTreeSum when it contains two in one: computation & iteration? The only chance is to construct a test tree and assert the result of the method call, in our case the sum against our expectation. And if the test fails you do not know wether was the computation algorithm wrong or was that the iteration? At the end to top it all off I tell you: according to Murphy’s Law the iteration will have a bug as well as the calculation. Both bugs in a combination will cause the sum to be accidentally exactly the same you expect and the test will PASS. J   Ok let’s use yield! That’s why it is generally a very good idea not to mix but isolate “things”. Ok let’s use yield!           private int CalculateTreeSumClean(Node top)         {             IEnumerable<Node> treeNodes = GetTreeNodes(top);             return CalculateSum(treeNodes);         }             private int CalculateSum(IEnumerable<Node> nodes)         {             int sumOfNodes = 0;             foreach (Node node in nodes)             {                 sumOfNodes += node.Value;             }             return sumOfNodes;         }           private IEnumerable<Node> GetTreeNodes(Node top)         {             yield return top;             foreach (Node childNode in top.ChildNodes)             {                 foreach (Node currentNode in GetTreeNodes(childNode))                 {                     yield return currentNode;                 }             }         }   Two methods does not know anything about each other. One contains calculation logic another jut the iteration logic. You can relpace the tree iteration algorithm from depth traversal to breath trevaersal or use stack or visitor pattern instead of recursion. This will not influence your calculation logic. And vice versa you can relace the sum with product or do whatever you want with node values, the calculateion algorithm is not aware of beeng working on some tree or graph.  How about not using yield? Now let’s ask the question – what if we do not have yield operator? The brief look at the generated code gives us an answer. The compiler generates a 150 lines long class to implement the iteration logic.       [CompilerGenerated]     private sealed class <GetTreeNodes>d__0 : IEnumerable<Node>, IEnumerable, IEnumerator<Node>, IEnumerator, IDisposable     {         ...        150 Lines of generated code        ...     }   Often we compromise code readability, cleanness, testability, etc. – to reduce number of classes, code lines, keystrokes and mouse clicks. This is the human nature - we are lazy. Knowing and using such a sexy construct like yield, allows us to be lazy, write very few lines of code and at the same time stay clean and do one thing in a method. That's why I generally welcome using staff like that.   Note: The above used recursive depth traversal algorithm is possibly the compact one but not the best one from the performance and memory utilization point of view. It was taken to emphasize on other primary aspects of this post.

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  • The underlying mechanism in 'yield return www' of Unity3D Game Engine

    - by thyandrecardoso
    In the Unity3D game engine, a common code sequence for getting remote data is this: WWW www = new WWW("http://remote.com/data/location/with/texture.png"); yield return www; What is the underlying mechanism here? I know we use the yield mechanism in order to allow the next frame to be processed, while the download is being completed. But what is going on under the hood when we do the yield return www ? What method is being called (if any, on the WWW class)? Is Unity using threads? Is the "upper" Unity layer getting hold of www instance and doing something?

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  • Is there a way to implement Caliburn-like co-routines in VB.NET since there's no yield keyword

    - by Miroslav Popovic
    Note that I'm aware of other yield in vb.net questions here on SO. I'm playing around with Caliburn lately. Bunch of great stuff there, including co-routines implementation. Most of the work I'm doing is C# based, but now I'm also creating an architecture guideline for a VB.NET only shop, based on Rob's small MVVM framework. Everything looks very well except using co-routines from VB. Since VB 10 is used, we can try something like Bill McCarthy's suggestion: Public Function Lines(ByVal rdr as TextReader) As IEnumerable(Of String) Return New GenericIterator(Of String) (Function(ByRef nextItem As String) As Boolean nextItem = rdr.ReadLine Return nextItem IsNot Nothing End Function) End Function I'm just failing to comprehend how a little more complex co-routine method like the one below (taken from Rob's GameLibrary) could be written in VB: public IEnumerable<IResult> ExecuteSearch() { var search = new SearchGames { SearchText = SearchText }.AsResult(); yield return Show.Busy(); yield return search; var resultCount = search.Response.Count(); if (resultCount == 0) SearchResults = _noResults.WithTitle(SearchText); else if (resultCount == 1 && search.Response.First().Title == SearchText) { var getGame = new GetGame { Id = search.Response.First().Id }.AsResult(); yield return getGame; yield return Show.Screen<ExploreGameViewModel>() .Configured(x => x.WithGame(getGame.Response)); } else SearchResults = _results.With(search.Response); yield return Show.NotBusy(); } Any idea how to achieve that, or any thoughts on using Caliburn co-routines in VB?

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  • How to Pythonically yield all values from a list?

    - by bodacydo
    Suppose I have a list that I wish not to return but to yield values from. What is the most Pythonic way to do that? Here is what I mean. Thanks to some non-lazy computation I have computed the list ['a', 'b', 'c', 'd'], but my code through the project uses lazy computation, so I'd like to yield values from my function instead of returning the whole list. I currently wrote it as following: List = ['a', 'b', 'c', 'd'] for item in List: yield item But this doesn't feel Pythonic to me. Looking forward to some suggestions, thanks. Boda Cydo.

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  • Is using YIELD a read-only way to return a collection?

    - by Eric
    I'm writing an interface which has a collection property which I want to be read only. I don't want users of the interface to be able to modify the collection. The typical suggestion I've found for creating a read only collection property is to set the type of the property to IEnumerable like this: private List<string> _mylist; public IEnumerable<string> MyList { get { return this._mylist; } } Yet this does not prevent the user from casting the IEnumerable back to a List and modifying it. If I use a Yield keyword instead of returning _mylist directly would this prevent users of my interface from being able to modify the collection. I think so because then I'm only returning the objects one by one, and not the actual collection. private List<string> _mylist; public IEnumerable<string> MyList { get { foreach(string str in this._mylist) { yield return str; } } }

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