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  • Impossible to use ref and out in Extension methods?

    - by Hun1Ahpu
    Why is it forbidden to call Extension method with ref modifier? This one is possible: public static void Change(ref TestClass testClass, TestClass testClass2) { testClass = testClass2; } And this one not: public static void ChangeWithExtensionMethod(this ref TestClass testClass, TestClass testClass2) { testClass = testClass2; } But why?

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  • Are programming languages and methods inefficient? (assembler and C knowledge needed)

    - by b-gen-jack-o-neill
    Hi, for a long time, I am thinking and studying output of C language compiler in assembler form, as well as CPU architecture. I know this may be silly to you, but it seems to me that something is very ineffective. Please, don´t be angry if I am wrong, and there is some reason I do not see for all these principles. I will be very glad if you tell me why is it designed this way. I actually truly believe I am wrong, I know the genius minds of people which get PCs together knew a reason to do so. What exactly, do you ask? I´ll tell you right away, I use C as a example: 1: Stack local scope memory allocation: So, typical local memory allocation uses stack. Just copy esp to ebp and than allocate all the memory via ebp. OK, I would understand this if you explicitly need allocate RAM by default stack values, but if I do understand it correctly, modern OS use paging as a translation layer between application and physical RAM, when address you desire is further translated before reaching actual RAM byte. So why don´t just say 0x00000000 is int a,0x00000004 is int b and so? And access them just by mov 0x00000000,#10? Because you wont actually access memory blocks 0x00000000 and 0x00000004 but those your OS set the paging tables to. Actually, since memory allocation by ebp and esp use indirect addressing, "my" way would be even faster. 2: Variable allocation duplicity: When you run application, Loader load its code into RAM. When you create variable, or string, compiler generates code that pushes these values on the top o stack when created in main. So there is actual instruction for do so, and that actual number in memory. So, there are 2 entries of the same value in RAM. One in form of instruction, second in form of actual bytes in the RAM. But why? Why not to just when declaring variable count at which memory block it would be, than when used, just insert this memory location?

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  • extension methods with generics - when does caller need to include type parameters?

    - by Greg
    Hi, Is there a rule for knowing when one has to pass the generic type parameters in the client code when calling an extension method? So for example in the Program class why can I (a) not pass type parameters for top.AddNode(node), but where as later for the (b) top.AddRelationship line I have to pass them? class Program { static void Main(string[] args) { // Create Graph var top = new TopologyImp<string>(); // Add Node var node = new StringNode(); node.Name = "asdf"; var node2 = new StringNode(); node2.Name = "test child"; top.AddNode(node); top.AddNode(node2); top.AddRelationship<string, RelationshipsImp>(node,node2); // *** HERE *** } } public static class TopologyExtns { public static void AddNode<T>(this ITopology<T> topIf, INode<T> node) { topIf.Nodes.Add(node.Key, node); } public static INode<T> FindNode<T>(this ITopology<T> topIf, T searchKey) { return topIf.Nodes[searchKey]; } public static void AddRelationship<T,R>(this ITopology<T> topIf, INode<T> parentNode, INode<T> childNode) where R : IRelationship<T>, new() { var rel = new R(); rel.Child = childNode; rel.Parent = parentNode; } } public class TopologyImp<T> : ITopology<T> { public Dictionary<T, INode<T>> Nodes { get; set; } public TopologyImp() { Nodes = new Dictionary<T, INode<T>>(); } }

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  • What are Class methods in Python for?

    - by Dave Webb
    I'm teaching myself Python and my most recent lesson was that Python is not Java, and so I've just spent a while turning all my Class methods into functions. I now realise that I don't need to use Class methods for what I would done with static methods in Java, but now I'm not sure when I would use them. All the advice I can find about Python Class methods is along the lines of newbies like me should steer clear of them, and the standard documentation is at its most opaque when discussing them. Does anyone have a good example of using a Class method in Python or at least can someone tell me when Class methods can be sensibly used?

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  • Should I be using abstract methods in this Python scenario?

    - by sfjedi
    I'm not sure my approach is good design and I'm hoping I can get a tip. I'm thinking somewhere along the lines of an abstract method, but in this case I want the method to be optional. This is how I'm doing it now... from pymel.core import * class A(object): def __init__(self, *args, **kwargs): if callable(self.createDrivers): self._drivers = self.createDrivers(*args, **kwargs) select(self._drivers) class B(A): def createDrivers(self, *args, **kwargs): c1 = circle(sweep=270)[0] c2 = circle(sweep=180)[0] return c1, c2 b = B() In the above example, I'm just creating 2 circle arcs in PyMEL for Maya, but I fully intend on creating more subclasses that may or may not have a createDrivers method at all! So I want it to be optional and I'm wondering if my approach is—well, if my approach could be improved?

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  • In scala can I pass repeated parameters to other methods?

    - by Fred Haslam
    Here is something I can do in java, take the results of a repeated parameter and pass it to another method: public void foo(String ... args){bar(args);} public void bar(String ... args){System.out.println("count="+args.length);} In scala it would look like this: def foo(args:String*) = bar(args) def bar(args:String*) = println("count="+args.length) But this won't compile, the bar signature expects a series of individual strings, and the args passed in is some non-string structure. For now I'm just passing around arrays. It would be very nice to use starred parameters. Is there some way to do it?

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  • Are programming languages and methods ineffective? (assembler and C knowledge needed)

    - by b-gen-jack-o-neill
    Hi, for a long time, I am thinking and studying output of C language compiler in asemlber form, as well as CPU architecture. I know this may be silly to you, but it seems to me that something is very ineffective. Please, don´t be angry if I am wrong, and there is some reason I do not see for all these principles. I will be very glad if you tell me why is it designed this way. I actually trully believe I am wrong, I know the genius minds of people which get PCs together knew a reason to do so. What exactly, do you ask? I´ll tell you right away, I use C as a example: 1, Stack local scope memory allocation: So, typical local memory allocation uses stack. Just copy esp to ebp and than allocate all the memory via ebp. OK, I would understand this if you explicitly need allocate RAM by default stack values, but if I do understand it correctly, modern OS use paging as a translation layer between application and physical RAM, when adress you desire is further translated before reaching actuall RAM byte. So why don´t just say 0x00000000 is int a,0x00000004 is int b and so? And access them just by mov 0x00000000,#10? Becouse you wont actually access memory blocks 0x00000000 and 0x00000004 but those your OS set the paging tables to. Actually, since memory allocation by ebp and esp use indirect adressing, "my" way would be even faster. 2, Variable allocation duplicitly: When you run aaplication, Loader load its code into RAM. When you create variable, or string, compiler generates code that pushes these values on the top o stack when created in main. So there is actuall instruction for do so, and that actuall number in memory. So, there are 2 entries of the same value in RAM. One in fomr of instruction, second in form of actuall bytes in the RAM. But why? Why not to just when declaring variable count at which memory block it would be, than when used, just insert this memory location?

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  • When should methods be made private?

    - by AaronSzy
    There are lots of times where i'm not sure whether a particular method should be made private or not. For example, i'm building a class right now, which, is responsible for generating a report. This class has a buildReport method and several methods which collect the necessary data for buildReport. // single public method // uses a set of helper methods public buildReport() // helper methods private avgSurveyTime() private fetchVendors() private fetchSendCounts() private ... Im debating whether i should make these helper methods public. The only method i really plan on calling outside at the moment is buildReport. However, it might be useful to get just a list of the vendors with fetchVendors etc. I see two schools of thought on this: You can always expose as little as possible. (In which case, many of my classes would only have one public method) OR you can expose all you can that might be useful to the user of the class. Is there a good rule of thumb to use for deciding when methods should be made public/private?

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  • Partial view links not working in Fire Fox

    - by user329540
    I have a MVC4 asp.net application, I have two layouts a main layout for the main page and a second layout for the nested pages. The problem I have is with the second layout, on this layout I call a partial view which has my navigation links. In IE the navigation menu displays fine and when each item is clicked it navigates as expected. However in FF when the page renders the navigation bar is displayed but it has no 'click functionality' if you will its as if its simply text. My layout of nested page: <header> <img src="../../Images/fronttop.png" id="nestedPageheader" alt="Background Img"/> <div class="content-wrapper"> <section > <nav> <div id="navcontainer"> </div> </nav> </section> <div> </header> The script to retreive partial view and information for dynamic links on layout page. <script type="text/javascript"> var menuLoaded = false; $(document).ready(function () { if($('#navcontainer')[0].innerHTML.trim() == "") { $.ajax({ url: "@Url.Content("~/Home/MenuLayout")", type: "GET", success: function (response, status, xhr) { var nvContainer = $('#navcontainer'); nvContainer.html(response); menuLoaded = true; }, error: function (XMLHttpRequest, textStatus, errorThrown) { var nvContainer = $('#navcontainer'); nvContainer.html(errorThrown); } }); } }); </script> May partial view: @model Mscl.OpCost.Web.Models.stuffmodel <div class="menu"> <ul> <li><a>@Html.ActionLink("Home", "Index", "Home")</a></li> <li><a>@Html.ActionLink("some stuff", "stuffs", "stuff")</a></li> <li> <h5><a><span>somestuff</span></a></h5> <ul> <li><a>stuffs1s</a> <ul> @foreach (var image in Model.stuffs.Where(g => g.Grouping == 1)) { <li> <a>@Html.ActionLink(image.Title, "stuffs", "stuff", new { Id = image.CategoryId }, null)</a> </li> } </ul> </li> </ul> </il> </ul> </div> I need to know why this works fine in IE but why its not working in FF(all versions). Any assistance would be appreciated.

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  • Online betting system design [closed]

    - by Rafal
    I am a Computer Science student, preparing for my exam in software engineering. I am strugging with answering one of the sample questions to the scenario below. My understanding is that the system design approach should probably be a mixture of agile and plan driven elements but - since I've no practical experience - it's hard for me to decide on the balance and tolls that should be used. I will appreciate any hints from experienced business analysts who were involved in similar kind of projects. Ray Sing is the owner of “Last Betz", a bookmakers with 7 outlets across Louth and Meath. With the advent of smartphones Ray would now like to allow his clients to place their bets online using their mobile devices. Clients would register for an account and password and would log their credit card details via the Last Betz website. To begin using the facility customers must 'load' their accounts with 100 euros. Any winnings, minus commission, will be placed in the account whilst any losses will be automatically deducted from the account. Assuming you have been selected to develop the above system: How would you approach the design of this system? Discuss the design methods and models you would use.

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  • javadoc and overloaded methods

    - by skrebbel
    Hi all, I'm developing an API with many identically named methods that just differ by signature, which I guess is fairly common. They all do the same thing, except that they initialize various values by defaults if the user does not want to specify. As a digestible example, consider public interface Forest { public Tree addTree(); public Tree addTree(int amountOfLeaves); public Tree addTree(int amountOfLeaves, Fruit fruitType); public Tree addTree(int amountOfLeaves, int height); public Tree addTree(int amountOfLeaves, Fruit fruitType, int height); } The essential action performed by all of these methods is the same; a tree is planted in the forest. Many important things users of my API need to know about adding trees hold for all these methods. Ideally, I would like to write one Javadoc block that is used by all methods: /** * Plants a new tree in the forest. Please note that it may take * up to 30 years for the tree to be fully grown. * * @param amountOfLeaves desired amount of leaves. Actual amount of * leaves at maturity may differ by up to 10%. * @param fruitType the desired type of fruit to be grown. No warranties * are given with respect to flavour. * @param height desired hight in centimeters. Actual hight may differ by * up to 15%. */ In my imagination, a tool could magically choose which of the @params apply to each of the methods, and thus generate good docs for all methods at once. With Javadoc, if I understand it correctly, all I can do is essentially copy&paste the same javadoc block five times, with only a slightly differing parameter list for each method. This sounds cumbersome to me, and is also difficult to maintain. Is there any way around that? Some extension to javadoc that has this kind of support? Or is there a good reason why this is not supported that I missed?

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  • MsChart : Partial view error

    - by Poomjai
    Hi I have a problem when i using Mschart on my MVC project, when i use the first index page of project to render for the partial view name index2 the code is <% Html.RenderPartial("Index2"); %> But when i run it the error is occur which the message is CS0029: Cannot implicitly convert type 'ASP.views_home_index2_ascx' to 'System.Web.UI.Page' -it said that the problem line of code is : // Render chart control Line 52: Chart2.Page = this; << At here Line 53: HtmlTextWriter writer = new HtmlTextWriter(Page.Response.Output); Line 54: Chart2.RenderControl(writer); But when i put all of code in Index2.ascx to the index.aspx and not to render the partial view it work fine Code of Index2.ascx is <% System.Web.UI.DataVisualization.Charting.Chart Chart2 = new System.Web.UI.DataVisualization.Charting.Chart(); Chart2.Width = 412; Chart2.Height = 296; Chart2.RenderType = RenderType.ImageTag; Chart2.Palette = ChartColorPalette.BrightPastel; Title t = new Title("No Code Behind Page", Docking.Top, new System.Drawing.Font("Trebuchet MS", 14, System.Drawing.FontStyle.Bold), System.Drawing.Color.FromArgb(26, 59, 105)); Chart2.Titles.Add(t); Chart2.ChartAreas.Add("Series 1"); Chart2.Series.Add("Series 1"); // add points to series 1 Chart2.Series["Series 1"].Points.AddY(3); Chart2.Series["Series 1"].Points.AddY(4); Chart2.Series["Series 1"].Points.AddY(5); Chart2.BorderSkin.SkinStyle = BorderSkinStyle.Emboss; Chart2.BorderColor = System.Drawing.Color.FromArgb(26, 59, 105); Chart2.BorderlineDashStyle = ChartDashStyle.Solid; Chart2.BorderWidth = 2; Chart2.Legends.Add("Legend1"); // Render chart control Chart2.Page = this; HtmlTextWriter writer = new HtmlTextWriter(Page.Response.Output); Chart2.RenderControl(writer); %

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  • UpdatePanel doesn't do partial-page update, and IsInAsyncPostBack is always false

    - by Joseph Anderson
    I'm attempting to use an UpdatePanel, but can't get partial-page updates to work. When I look at the ScriptManager's IsInAsyncPostBack property, it's always false. Here's a page that reproduces the issue. It has a ScriptManager, an UpdatePanel, a LinkButton within the update panel, and a Button wired up to the UpdatePanel via the Triggers collection. <%@ Page Language="C#" %> <script runat="server"> protected void Page_Load(object sender, EventArgs e) { Label1.Text = DateTime.Now.ToString(); if (IsPostBack) Label1.Text += " - Postback!"; if (ScriptManager1.IsInAsyncPostBack) Label1.Text += " - Async!"; } </script> <html xmlns="http://www.w3.org/1999/xhtml"> <body> <form id="form1" runat="server"> <asp:ScriptManager ID="ScriptManager1" EnablePartialRendering="true" runat="server" /> <asp:UpdatePanel ID="UpdatePanel1" UpdateMode="Conditional" runat="server"> <ContentTemplate>Panel 1:<asp:Label runat=server ID=Label1 /><br /> <asp:LinkButton runat=server ID="LinkButton1" Text="Update!"></asp:LinkButton></ContentTemplate> <Triggers><asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" /></Triggers> </asp:UpdatePanel> <asp:Button ID="Button1" Text="Refresh Panel 1" runat="server" UseSubmitBehavior=false /> </form> </body> </html> If I run this code and click on either of the buttons, I see "Panel 1:2/8/2010 3:38:41 PM - Postback!" I expected that clicking either button would cause a partial-page update for UpdatePanel1, that IsInAsyncPostBack would be true, and that " - Async!" would be appended to Label1. Any idea why IsInAsyncPostBack is always false?

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  • Unit test complex classes with many private methods

    - by Simon G
    Hi, I've got a class with one public method and many private methods which are run depending on what parameter are passed to the public method so my code looks something like: public class SomeComplexClass { IRepository _repository; public SomeComplexClass() this(new Repository()) { } public SomeComplexClass(IRepository repository) { _repository = repository; } public List<int> SomeComplexCalcualation(int option) { var list = new List<int>(); if (option == 1) list = CalculateOptionOne(); else if (option == 2) list = CalculateOptionTwo(); else if (option == 3) list = CalculateOptionThree(); else if (option == 4) list = CalculateOptionFour(); else if (option == 5) list = CalculateOptionFive(); return list; } private List<int> CalculateOptionOne() { // Some calculation } private List<int> CalculateOptionTwo() { // Some calculation } private List<int> CalculateOptionThree() { // Some calculation } private List<int> CalculateOptionFour() { // Some calculation } private List<int> CalculateOptionFive() { // Some calculation } } I've thought of a few ways to test this class but all of them seem overly complex or expose the methods more than I would like. The options so far are: Set all the private methods to internal and use [assembly: InternalsVisibleTo()] Separate out all the private methods into a separate class and create an interface. Make all the methods virtual and in my tests create a new class that inherits from this class and override the methods. Are there any other options for testing the above class that would be better that what I've listed? If you would pick one of the ones I've listed can you explain why? Thanks

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  • UIWebView: webViewDidStartLoad/webViewDidFinishLoad delegate methods not called when loading certain URLs

    - by Dia
    I have basic web browser implemented using a UIWebView. I've noticed that for some pages, none of the UIWebViewDelegate methods are called. An example page in which this happens is: http://www.youtube.com/user/google. Here are the steps to reproduce the issue (make sure you insert NSLog calls in your controller's UIWebViewDelegate methods): Load the above youtube URL into the UIWebView [notice that here, the UIWebViewDelegate methods do get called when the page loads] Touch the "Uploads" category on the page Touch any video in that category [issue: notice that a new page is loaded, but none of the UIWebView delegates are called] I know that this is not an issue of UIWebView's delegate not being set properly, since the delegate methods do get invoked when loading other links (e.g. if you try clicking on a link that takes you outside of youtube, you'll notice the delegate methods getting called). My gut feeling initially was that it might be because the page is loaded using AJAX, which may not invoke the delegate method. But then when I checked Safari, it did not exhibit this problem, so it must be something on my side. I've also noticed that Three20's TTWebController has the exact same issue as I'm having. But the problem that arises from this issue is that without the delegate methods called, I'm unable to update the UI to enable/disable the back and forward browsing buttons when new requests are loaded. And idea why this is happening or how can I work around it to update the UI when a new request is made?

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  • designing an ASP.NET MVC partial view - showing user choices within a large set of choices

    - by p.campbell
    Consider a partial view whose job is to render markup for a pizza order. The desire is to reuse this partial view in the Create, Details, and Update views. It will always be passed an IEnumerable<Topping>, and output a multitude of checkboxes. There are lots... maybe 40 in all (yes, that might smell). A-OK so far. Problem The question is around how to include the user's choices on the Details and Update views. From the datastore, we've got a List<ChosenTopping>. The goal is to have each checkbox set to true for each chosen topping. What's the easiest to read, or most maintainable way to achieve this? Potential Solutions Create a ViewModel with the List and List. Write out the checkboxes as per normal. While writing each, check whether the ToppingID exists in the list of ChosenTopping. Create a new ViewModel that's a hybrid of both. Perhaps call it DisplayTopping or similar. It would have property ID, Name and IsUserChosen. The respective controller methods for Create, Update, and Details would have to create this new collection with respect to the user's choices as they see fit. The Create controller method would basically set all to false so that it appears to be a blank slate. The real application isn't pizza, and the organization is a bit different from the fakeshot, but the concept is the same. Is it wise to reuse the control for the 3 different scenarios? How better can you display the list of options + the user's current choices? Would you use jQuery instead to show the user selections? Any other thoughts on the potential smell of splashing up a whole bunch of checkboxes?

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  • HOWTO: implement a jQuery version of ASP.Net MVC "Strongly Typed Partial Views"

    - by Sam Carleton
    I am working on a multi-page assessment form where the questions/responses are database driven. Currently I the basic system working with Html.BeginForm via standard ASP.Net MVC. At this point in time, the key to the whole system is the 'Strongly Typed Partial Views'. When the question/response is read from the database, the response type determines which derived model is created and added to the collection. The main view it iterates through the collection and uses the 'Strongly Typed Partial Views' system of ASP.Net MVC to determine which view to render the correct type of response (radio button, drop down, or text box). I would like to change this process from a Html.BeginForm to Ajax.BeginForm. The problem is I don't have a clue as to how to implement the dynamic creation of the question/response in the JavaScript/jQuery world. Any thoughts and/or suggestions? Here is the current code to generate the dynamic form: @using (Html.BeginForm(new { mdsId = @Model.MdsId, sectionId = @Model.SectionId })) { <div class="SectionTitle"> <span>Section @Model.SectionName - @Model.SectionDescription</span> <span style="float: right">@Html.CheckBoxFor(x => x.ShowUnansweredQuestions) Show only unaswered questions</span> </div> @Html.HiddenFor(x => x.PrevSectionId) @Html.HiddenFor(x => x.NextSectionId) for (var i = 0; i < Model.answers.Count(); i++) { @Html.EditorFor(m => m.answers[i]); } }

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  • Rails partial gets double escaped when using link_to_function

    - by dombesz
    Hi, I have the following code. def add_resume_link(name, form) link_to_function name do |page| html = form.fields_for :resumes, @general_resume.resumes.build, :child_index => 'NEW_RECORD' do |form_parent| render :partial => 'resume_form', :locals=>{:form=>form_parent} end page << "$('resumes').insert({ bottom: '#{escape_javascript(html)}'.replace(/NEW_RECORD/g, id) });" end end And on the resume_form i have somewhere: =add_skill_link("Add Skill", form, "resume_#{id}_skills") and the function looks like: def add_skill_link(name, form, id) link_to_function name do |page| html = form.fields_for :skill_items, @general_resume.skill_items.build, :child_index => 'NEW_RECORD' do |form_parent| render :partial=>'skill_form', :locals=>{:form=>form_parent, :parent=>id} end page << "$('#{id}').insert({ bottom: '#{escape_javascript(html)}'.replace(/NEW_RECORD/g, new Date().getTime()) });" end end So basically i have a javascript code which dinamically adds a piece of html (add_resume) and contains another javascript code which dinamically adds a select box to the page. My problem is that the add_skill_link works fine if i use from the server side, i mean rendering from server side. And gets double escaped when using within the upper described way. I tried to remove the escape_javascript from the add_skill_link bit still not good. Any ideas?

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  • What to call factory-like (java) methods used with immutable objects

    - by StaxMan
    When creating classes for "immutable objects" immutable meaning that state of instances can not be changed; all fields assigned in constructor) in Java (and similar languages), it is sometimes useful to still allow creation of modified instances. That is, using an instance as base, and creating a new instance that differs by just one property value; other values coming from the base instance. To give a simple example, one could have class like: public class Circle { final double x, y; // location final double radius; public Circle(double x, double y, double r) { this.x = x; this.y = y; this.r = r; } // method for creating a new instance, moved in x-axis by specified amount public Circle withOffset(double deltaX) { return new Circle(x+deltaX, y, radius); } } So: what should method "withOffset" be called? (note: NOT what its name ought to be -- but what is this class of methods called). Technically it is kind of a factory method, but somehow that does not seem quite right to me, since often factories are just given basic properties (and are either static methods, or are not members of the result type but factory type). So I am guessing there should be a better term for such methods. Since these methods can be used to implement "fluent interface", maybe they could be "fluent factory methods"? Better suggestions? EDIT: as suggested by one of answers, java.math.BigDecimal is a good example with its 'add', 'subtract' (etc) methods. Also: I noticed that there's this question (by Jon Skeet no less) that is sort of related (although it asks about specific name for method)

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  • Passing null child object from parent object to a partial view

    - by Mike
    I have an object which contains models for my ASP.NET MVC web app. The Model that is being passed into the view has sub models for "gadgets" on that particular view. Each of these sub models gets passed to a partial view (gadget). The problem is when I have a null model in the view model. See example below. View Model: public class FooBarHolder() { public FooBar1 FooBar1 { get; set; } public FooBar2 FooBar2 { get; set; } } We pass FooBarHolder into the view and inside the view we make calls such as <% Html.RenderPartial("Foo", Model.FooBar1); %> <% Html.RenderPartial("Foo2", Model.FooBar2); %> Now say for instance that Model.FooBar2 was null. What I am experiencing from the strongly typed partial view is an error that says "This view expected a model of type FooBar2 but got a model of type FooBarHolder." Why is this happening instead of just passing in a null?

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  • sending specific data into a collection partial

    - by mikeglaz
    I have a User class with a has_many :messages and a Message class which belongs_to :user. In the Message controller's show action has the corresponding view: <% if @messages.any? %> <ol class="microposts"> <%= render partial: 'shared/message', collection: @messages %> </ol> <% end %> And the shared/_message.html.erb template looks like this: <li id="<%= message.id %>"> <span class="content"><%= message.body %></span> <% user_id = message.from %> <% user = User.find(user_id) %> From: <%= user.name %> </li> I feel like the following two lines should be done in the Messages controller from what I read in tutorials on Rails: <% user_id = message.from %> <% user = User.find(user_id) %> But how would I pass each message's corresponding from value (which stores user.id) into the partial? thanks, mike

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  • What are the tradeoffs for using 'partial view models'?

    - by Kenny Evitt
    I've become aware of an itch due to some non-DRY code pertaining to view model classes in an (ASP.NET) MVC web application and I'm thinking of scratching my itch by organizing code in various 'partial view model' classes. By partial-view-model, I'm referring to a class like a view model class in an analogous way to how partial views are like views, i.e. a way to encapsulate common info and behavior. To strengthen the 'analogy', and to aid in visually organizing the code in my IDE, I was thinking of naming the partial-view-model classes with a _ prefix, e.g. _ParentItemViewModel. As a slightly more concrete example of why I'm thinking along these lines, imagine that I have a domain-model-entity class ParentItem and the user-friendly descriptive text that identifies these items to users is complex enough that I'd like to encapsulate that code in a method in a _ParentItemViewModel class, for which I can then include an object or a collection of objects of that class in all the view model classes for all the views that need to include a reference to a parent item, e.g. ChildItemViewModel can have a ParentItem property of the _ParentItemViewModel class type, so that in my ChildItemView view, I can use @Model.ParentItem.UserFriendlyDescription as desired, like breadcrumbs, links, etc. Edited 2014-02-06 09:56 -05 As a second example, imagine that I have entity classes SomeKindOfBatch, SomeKindOfBatchDetail, and SomeKindOfBatchDetailEvent, and a view model class and at least one view for each of those entities. Also, the example application covers a lot more than just some-kind-of-batches, so that it wouldn't really be useful or sensible to include info about a specific some-kind-of-batch in all of the project view model classes. But, like the above example, I have some code, say for generating a string for identifying a some-kind-of-batch in a user-friendly way, and I'd like to be able to use that in several views, say as breadcrumb text or text for a link. As a third example, I'll describe another pattern I'm currently using. I have a Contact entity class, but it's a fat class, with dozens of properties, and at least a dozen references to other fat classes. However, a lot of view model classes need properties for referencing a specific contact and most of those need other properties for collections of contacts, e.g. possible contacts to be referenced for some kind of relationship. Most of these view model classes only need a small fraction of all of the available contact info, basically just an ID and some kind of user-friendly description (i.e. a friendly name). It seems to be pretty useful to have a 'partial view model' class for contacts that all of these other view model classes can use. Maybe I'm just misunderstanding 'view model class' – I understand a view model class as always corresponding to a view. But maybe I'm assuming too much.

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