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• Can an aggregate root hold references of members of another aggregate root?

  - by Rushino

  Hello, I know outside aggregates cant change anything inside an aggregate without passing by his root. That said i would like to know if an aggregate root can hold references of members (objects insides) of another aggregate root? (fellowing DDD rules) Example : a Calendar contain a list of phases which contain a list of sequences which contain a list of assignations Calendar is root because phases and sequences and assignations only work in context of a calendar. You also have Students and Groups of student (called groups) It is possible (fellowing DDD rules) to make Groups holding references of assignations or it need to pass by the root for accessing groups from assignations ? Thanks.

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• Low coupling processing big quantities of data

  - by vitalik

  Usually I achieve low coupling by creating classes that exchange lists, sets, and maps between them. Now I am developing a batch application and I can't put all the data inside a data structure because there isn't enough memory. I have to read and process one chunk of data and then going to the next one. So having low coupling is much more difficult because I have to check somewhere if there is still data to read, etc. What I am using now is: Source - Process - Persist The classes that process have to ask to the Source classes if there are more rows to read. What are the best practices and or useful patterns in such situations? I hope I am explaining myself, if not tell me.

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• Where should I draw the line between unit tests and integration tests? Should they be separate?

  - by Earlz

  I have a small MVC framework I've been working on. It's code base definitely isn't big, but it's not longer just a couple of classes. I finally decided to take the plunge and start writing tests for it(yes, I know I should've been doing that all along, but it's API was super unstable up until now) Anyway, my plan is to make it extremely easy to test, including integration tests. An example integration test would go something along these lines: Fake HTTP request object - MVC framework - HTTP response object - check the response is correct Because this is all doable without any state or special tools(browser automation etc), I could actually do this with ease with regular unit test frameworks(I use NUnit). Now the big question. Where exactly should I draw the line between unit tests and integration tests? Should I only test one class at a time(as much as possible) with unit tests? Also, should integration tests be placed in the same testing project as my unit testing project?

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• Dependency Injection/IoC container practices when writing frameworks

  - by Dave Hillier

  I've used various IoC containers (Castle.Windsor, Autofac, MEF, etc) for .Net in a number of projects. I have found they tend to encourage a number of bad practices. Are there any established practices for IoC container use, particularly when providing a platform/framework? My aim as a framework writer is to make code as simple and as easy to use as possible. I'd rather write one line of code to construct an object than ten or even just two. For example, a couple of code smells that I've noticed and don't have good suggestions to: Large number of parameters (5) for constructors. Creating services tends to be complex; all of the dependencies are injected via the constructor - despite the fact that the components are rarely optional (except for maybe in testing). Lack of private and internal classes; this one may be a specific limitation of using C# and Silverlight, but I'm interested in how it is solved. It's difficult to tell what a frameworks interface is if all the classes are public; it allows me access to private parts that I probably shouldnt touch. Coupling the object lifecycle to the IoC container. It is often difficult to manually construct the dependencies required to create objects. Object lifecycle is too often managed by the IoC framework. I've seen projects where most classes are registered as Singletons. You get a lack of explicit control and are also forced to manage the internals (it relates to the above point, all classes are public and you have to inject them). For example, .Net framework has many static methods. such as, DateTime.UtcNow. Many times I have seen this wrapped and injected as a construction parameter. Depending on concrete implementation makes my code hard to test. Injecting a dependency makes my code hard to use - particularly if the class has many parameters. How do I provide both a testable interface, as well as one that is easy to use? What are the best practices?

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• Is an undergraduate degree in CS required?

  - by Girish

  I will complete my undergrad in Material Science this spring. I am not interested in the subject but I am very interested in Computer Science and programming and have decided to make the shift. Do you think I should first get an undergraduate degree in Computer Science or should I apply for a master's program? My programming skills are pretty decent, but I lack a lot of concrete knowledge in algorithms and data structures? Will a master's degree help me with the basics?

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• Au revoir, Python?

  - by GuySmiley

  I'm an ex-C++ programmer who's recently discovered (and fallen head-over-heels with) Python. I've taken some time to become reasonably fluent in Python, but I've encountered some troubling realities that may lead me to drop it as my language of choice, at least for the time being. I'm writing this in the hopes that someone out there can talk me out of it by convincing me that my concerns are easily circumvented within the bounds of the python universe. I picked up python while looking for a single flexible language that will allow me to build end-to-end working systems quickly on a variety of platforms. These include: - web services - mobile apps - cross-platform client apps for PC Development speed is more of a priority at the time-being than execution speed. However, in order to improve performance over time without requiring major re-writes or architectural changes I think it's imperative to be able to interface easily with Java. That way, I can use Java to optimize specific components as the application scales, without throwing away any code. As far as I can tell, my requirement for an enterprise-capable, platform-independent, fast language with a large developer base means it would have to be Java. .NET or C++ would not cut it due to their respective limitations. Also Java is clearly de rigeur for most mobile platforms. Unfortunately, tragically, there doesn't seem to be a good way to meet all these demands. Jython seems to be what I'm looking for in principle, except that it appears to be practically dead, with no one developing, supporting, or using it to any great degree. And also Jython seems too married to the Java libraries, as you can't use many of the CPython standard libraries with it, which has a major impact on the code you end up writing. The only other option that I can see is to use JPype wrapped in marshalling classes, which may work although it seems like a pain and I wonder if it would be worth it in the long run. On the other hand, everything I'm looking for seems to be readily available by using JRuby, which seems to be much better supported. As things stand, I think this is my best option. I'm sad about this because I absolutely love everything about Python, including the syntax. The perl-like constructs in Ruby just feel like such a step backwards to me in terms of readability, but at the end of the day most of the benefits of python are available in Ruby as well. So I ask you - am I missing something here? Much of what I've said is based on what I've read, so is this summary of the current landscape accurate, or is there some magical solution to the Python-Java divide that will snuff these concerns and allow me to comfortably stay in my happy Python place?

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• Databinding to an Entity Framework in WPF

  - by King Chan

  Is it good to use databinding to Entity Framework's Entity in WPF? I created a singleton entity framework context: To have only one connection and it won't open and close all the time. So I can pass the Entity around to any class, and can modify the Entity and make changes to the database. All ViewModels getting the entity out from the same Context and databinding to the View saves me time from mapping new object, but now I imagine there is problem in not using the newest Context: A ViewModel databinding to a Entity, then someone else updated the data. The ViewModel will still display the old data, because the Context is never being dispose to refresh. I always create new Context and then dispose of it. If I want to pass the Entity around, then there will be conflicts between Context and Entity. What is the suggested way of doing this ?

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• scalablity of Scala over Java

  - by Marcus

  I read an article that says Scala handles concurrency better than Java. http://www.theserverside.com/feature/Solving-the-Scalability-Paradox-with-Scala-Clojure-and-Groovy ...the scalability limitation is confined specifically to the Java programming language itself, but it is not a limitation of the Java platform as a whole... The scalability issues with Java aren't a new revelation. In fact, plenty of work has been done to address these very issues, with two of the most successful projects being the programming languages named Scala and Clojure... ...Scala is finding ways around the problematic thread and locking paradigm of the Java language... How is this possible? Doesn't Scala use Java's core libraries which brings all the threading and locking issues from Java to Scala?

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• Are Language Comparisons Meaningful?

  - by Prasoon Saurav

  Dr Bjarne Stroustrup in his book D&E says Several reviewers asked me to compare C++ to other languages. This I have decided against doing. Thereby, I have reaffirmed a long-standing and strongly held view: "Language comparisons are rarely meaningful and even less often fair" . A good comparison of major programming languages requires more effort than most people are willing to spend, experience in a wide range of application areas, a rigid maintenance of a detached and impartial point of view, and a sense of fairness. I do not have the time, and as the designer of C++, my impartiality would never be fully credible. -- The Design and Evolution of C++(Bjarne Stroustrup) Do you people agree with his this statement "Language comparisons are rarely meaningful and even less often fair"? Personally I think that comparing a language X with Y makes sense because it gives many more reasons to love/despise X/Y :-P What do you people think?

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• Are C++ templates just a kind of glorified macros?

  - by Gulshan

  From different comparisons among C++ templates and C#/Java generics like this one- http://stackoverflow.com/questions/31693/what-are-the-differences-between-generics-in-c-and-java-and-templates-in-c/31929#31929 I have a got a perception that, C++ templates are implemented by some kind of preprocessing, not compiling. In other words, they are just a kind of C macros. Is this right? Then I felt that, if C++ templates are implemented by preprocessing, dynamic linking(.dll) cannot be used. A quick google search also supports this. And lastly, how can we use macros in C to deliver C++ templates like functionalities? Another thing came in my mind about templates similar to some kind of preprocessor that, there can be integers passed as arguments to some templates. And it even supports kind of recursion. But the recursion is not in the assembly/machine code. So, am I wrong calling templates glorified macros? Unlike normal macros, it has some superior abilities. But isn't it a kind of preprocessing?

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• How does key-based caching work?

  - by Dominic Santos

  I recently read an article on the 37Signals blog and I'm left wondering how it is that they get the cache key. It's all well and good having a cache key that includes the object's timestamp (this means that when you update the object the cache will be invalidated); but how do you then use the cache key in a template without causing a DB hit for the very object that you are trying to fetch from the cache. Specifically, how does this affect One to Many relations where you are rendering a Post's Comments for example. Example in Django: {% for comment in post.comments.all %} {% cache comment.pk comment.modified %} <p>{{ post.body }}</p> {% endcache %} {% endfor %} Is caching in Rails different to just requests to memcached for example (I know that they convert your cache key to something different). Do they also cache the cache key?

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• When using method chaining, do I reuse the object or create one?

  - by MainMa

  When using method chaining like: var car = new Car().OfBrand(Brand.Ford).OfModel(12345).PaintedIn(Color.Silver).Create(); there may be two approaches: Reuse the same object, like this: public Car PaintedIn(Color color) { this.Color = color; return this; } Create a new object of type Car at every step, like this: public Car PaintedIn(Color color) { var car = new Car(this); // Clone the current object. car.Color = color; // Assign the values to the clone, not the original object. return car; } Is the first one wrong or it's rather a personal choice of the developer? I believe that he first approach may quickly cause the intuitive/misleading code. Example: // Create a car with neither color, nor model. var mercedes = new Car().OfBrand(Brand.MercedesBenz).PaintedIn(NeutralColor); // Create several cars based on the neutral car. var yellowCar = mercedes.PaintedIn(Color.Yellow).Create(); var specificModel = mercedes.OfModel(99).Create(); // Would `specificModel` car be yellow or of neutral color? How would you guess that if // `yellowCar` were in a separate method called somewhere else in code? Any thoughts?

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• What have you learnt that has a steep learning curve?

  - by Jonathan Khoo

  Recently, I've invested time in learning the intricacies of Git and it has got me thinking about time and learning. (My previous experience with version control systems was only limited use of CVS and SVN.) It took me a whole day's worth of reading to be able to understand the concepts and differences of Git. There are an infinite number of things available for us to learn. Some, more useful than others. I don't know Fortran - I'm relatively young. But looking back at the preceding years of my life, I notice that I'm busier and busier as time goes on. The amount of things I have to get through in a day is increasingly out of my control. It doesn't take a genius to extrapolate that information and realise I'll have even less time in the future - unless I get fired, but I have no strong plans relating to that idea for now. So, given that I have much more time and energy now than I will have in the future: what have you learnt, that has a steep learning curve, that you would possibly recommend to a fellow programmer? Edit: I've stumbled upon the excellent question What programming skills have provided you the best return on investment? and hav realised that my way of approaching how to spend learning time was naive - it doesn't matter if ten useful concepts can be learnt in the time of one if they're worth it.

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• Cross-platform desktop programming: C++ vs. Python

  - by John Wells

  Alright, to start off, I have experience as an amateur Obj-C/Cocoa and Ruby w/Rails programmer. These are great, but they aren't really helpful for writing cross-platform applications (hopefully GNUStep will one day be complete enough for the first to be multi platform, but that day is not today). C++, from what I can gather, is extremely powerful but also a huge, ugly behemoth that can take half a decade or more to master. I've also read that you can very easily not only shoot yourself in the foot, but blow your entire leg off with it since memory management is all manual. Obviously, this is all quite intimidating. Is it correct? Python seems to provide most of the power of C++ and is much easier to pick up at the cost of speed. How big is this sacrifice? Is it meaningful or can it be ignored? Which will have me writing fast, stable, highly reliable applications in a reasonable amount of time? Also, is it better to use Qt for your UI or instead maintain separate, native front ends for each platform? EDIT: For extra clarity, there are two types applications I want to write: one is an extremely friendly and convenient database frontend and the other, which no doubt will come much later on, is a 3D world editor.

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• Python class representation under the hood

  - by decentralised

  OK, here is a simple Python class: class AddSomething(object): __metaclass__ = MyMetaClass x = 10 def __init__(self, a): self.a = a def add(self, a, b): return a + b We have specified a metaclass, and that means we could write something like this: class MyMetaClass(type): def __init__(cls, name, bases, cdict): # do something with the class Now, the cdict holds a representation of AddSomething: AddSomething = type('AddSomething', (object,), {'x' : 10, '__init__': __init__, 'add': add}) So my question is simple, are all Python classes represented in this second format internally? If not, how are they represented? EDIT - Python 2.7

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• Modified Strategy Design Pattern

  - by Samuel Walker

  I've started looking into Design Patterns recently, and one thing I'm coding would suit the Strategy pattern perfectly, except for one small difference. Essentially, some (but not all) of my algorithms, need an extra parameter or two passed to them. So I'll either need to pass them an extra parameter when I invoke their calculate method or store them as variables inside the ConcreteAlgorithm class, and be able to update them before I call the algorithm. Is there a design pattern for this need / How could I implement this while sticking to the Strategy Pattern? I've considered passing the client object to all the algorithms, and storing the variables in there, then using that only when the particular algorithm needs it. However, I think this is both unwieldy, and defeats the point of the strategy pattern. Just to be clear I'm implementing in Java, and so don't have the luxury of optional parameters (which would solve this nicely).

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• Ruby Shoes for non-trivial apps

  - by marcof

  I've been taking a look at Ruby Shoes for GUI development with Ruby. So far, it's been a pretty good experience for making simple apps. However, I am quite worried about being able to write large scale applications with it. For example, how would I go about using MVP pattern with this framework ? For now, I have not been able to not make presentation concerns leak into the view because of the lack of some kind of "data binding". I have code that looks like this : Shoes.app do @view = SampleView.new @presenter = SamplePresenter.new @view @label = para @view.sample_property button "Update sample_property" do @presenter.update_sample_property end end Here, the call to @presenter.update_sample_property updates @view.sample_property but the label is not updated accordingly. For this to work, I would have to make @presenter.update_sample_property to return a string, and then call @label.text = return_value, but I think that would violate the MVP principle of not having presentation logic in the view. I'm used to work in .Net with the MVP pattern so I don't know if the pattern applies correctly to Shoes like I tried to do. Are there any ressources out there for making non-trivial apps with Shoes ? Especially using the MVP pattern or something similar ? EDIT : I took a look at the shoebox to see what other people have achieved with the framework. Though I did not look through it extensively, at first sight it seems like they are all simple projects with no real purposes.

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• How to turn on/off code modules?

  - by Safran Ali

  I am trying to run multiple sites using single code base and code base consist of the following module (i.e. classes) User module Q & A module Faq module and each class works on MVC pattern i.e. it consist of Entity class Helper class (i.e. static class) View (i.e. pages and controls) and let's say I have 2 sites site1.com and site2.com. And I am trying to achieve following functionality site1.com can have User, Q & A and Faq module up and running site2.com can have User and Q & A module live while Faq module is switched off but it can be turned-on if needed, so my query here is what is the best way to achieve such functionality Do I introduce a flag bit that I check on every page and control belonging to that module? It's more like CMS where you can turn on/off different features. I am trying to get my head around it, please provide me with an example or point out if I am taking the wrong approach.

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• What's the difference between implementing an Interface explicitly or implicitly?

  - by Rachel

  In Visual Studio I can right-click on an interface and choose to Implement Interface, or Implement Interface Explicitly. public class Test : ITest { public string Id // Generated by Implement Interface { get { throw new NotImplementedException(); } } string ITest.Id // Generated by Implement Interface Explicitly { get { throw new NotImplementedException(); } } } The only difference I see between the two is that the Interface name is added to the interface properties and methods when they're created if you choose to Implement Interface Explicitly. I find it makes the code a bit more readable since I can see where that method/property comes from, however does this make any difference in how the class is used or compiled? And does it really matter if I implement my interfaces implicitly or explicitly?

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• Can an issue tracking system be distributed?

  - by Klaim

  I was thinking about issue tracking software like Redmine, Trac or even the one that is in Fossil and something hit me: Is there a reason why Redmine and Trac are not possible to be distributed? Or maybe it's possible and I just don't know how it's possible? If it's not possible, why? By distributed I mean like Facebook or Google or other applications that effectively runs on multiple hardware a the same time but share data.

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• Is it possible to implement an infinite IEnumerable without using yield with only C# code?

  - by sinelaw

  This isn't a practical problem, it's more of a riddle. Problem I'm curious to know if there's a way to implement something equivalent to the following, but without using yield: IEnumerable<T> Infinite<T>() { while (true) { yield return default(T); } } Rules You can't use the yield keyword Use only C# itself directly - no IL code, no constructing dynamic assemblies etc. You can only use the basic .NET lib (only mscorlib.dll, System.Core.dll? not sure what else to include). However if you find a solution with some of the other .NET assemblies (WPF?!), I'm also interested. Don't implement IEnumerable or IEnumerator. Notes The closest I've come yet: IEnumerable<int> infinite = null; infinite = new int[1].SelectMany(x => new int[1].Concat(infinite)); This is "correct" but hits a StackOverflowException after 14399 iterations through the enumerable (not quite infinite). I'm thinking there might be no way to do this due to the CLR's lack of tail recursion optimization. A proof would be nice :)

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• Block elements vs inline elements in HTML: why the distinction?

  - by EpsilonVector

  The distinction between block and inline elements always seemed strange to me. The whole difference is that a block element takes up the entire width thus forcing a line break before and after the element, and an inline element only takes up as much as the content. Why not just have one type of element- an inline element where you can also apply custom height/width, and use that? You want line breaks? Insert a <br />, or maybe add a special tag in the CSS for that behavior. The way it's now, I don't see it solving any problem, and instead it only forces a property that in my opinion should be decided by a designer. So why the two types?

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• Why does void in C mean not void?

  - by Naftuli Tzvi Kay

  In strongly-typed languages like Java and C#, void (or Void) as a return type for a method seem to mean: This method doesn't return anything. Nothing. No return. You will not receive anything from this method. What's really strange is that in C, void as a return type or even as a method parameter type means: It could really be anything. You'd have to read the source code to find out. Good luck. If it's a pointer, you should really know what you're doing. Consider the following examples in C: void describe(void *thing) { Object *obj = thing; printf("%s.\n", obj->description); } void *move(void *location, Direction direction) { void *next = NULL; // logic! return next; } Obviously, the second method returns a pointer, which by definition could be anything. Since C is older than Java and C#, why did these languages adopt void as meaning "nothing" while C used it as "nothing or anything (when a pointer)"?

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• Representation of data in application versus database

  - by user1815201

  I'm going to make an application that will be given data to put in a database. The data will for the most part be the same, but the way it is formatted will vary a lot (could be in anything from text files to .xls to .doc). I'm not a very experienced developer, but I can see some potential issues and I want to minimize them. First off I have decided to use the DAO pattern, so that I can easily support new file formats or file suddenly formatted in different ways. What I really wonder about though, is how I should manage the data itself within my application. I'm thinking that the database DAO should have models representing each table of the database with the same relations between them, to make the uploading process easy. But should the filesystem DAO's have to use the same models? I can imaging that when the database changes, the change will suddenly propagate throughout the entire system, all DAOs and models alike. And that is obviously a bad thing. I'm a little bit tired and out of time. Will update with what ever questions you have. Thanks!

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• Good resources for learning Rails?

  - by Bobby Tables

  I just finished working through Peter Cooper's "Beginning Ruby". So now I've got a reasonable grounding in the Ruby language and would like to move onto learning Rails. This question's answers give some good pointers, but I'd like to hear some specific reviews of books and online materials. I generally learn best by working through books with good practical/technical examples AND some passive reading content that breaks up the study between practical and reading sessions (this is what made "Beginning Ruby" great for me), but I'm worried that RoR is evolving fast and that any printed book I order might be obsolete by the time I get it and work through it. Is this a fair worry? Or can anyone recommend a good Rails 3 book that should be up to date at least for the next year or so? Also, I had a brief look at some of the online resources from the other questions, and Rails for Zombies seems to get a lot of praise. Has anyone here actually used it as their introductory guide to Rails? Basically I'd like to hear first-hand accounts of people who went through this "Ruby-to-Rails" learning phase recently and which materials were useful to you.

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