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  • Best design for generating code from an AST?

    - by Sam Washburn
    I'm working on a pretty complex DSL that I want to compile down into a few high level languages. The whole process has been a learning experience. The compiler is written in java. I was wondering if anyone knew a best practice for the design of the code generator portion. I currently have everything parsed into an abstract syntax tree. I was thinking of using a template system, but I haven't researched that direction too far yet as I would like to hear some wisdom first from stack overflow. Thanks!

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  • django modeling

    - by SledgehammerPL
    Concept: Drinks are made of components. E.g. 10ml of Vodka. In some receipt the component is very particular (10ml of Finlandia Vodka), some not (10 ml of ANY Vodka). I wonder how to model a component to solve this problem - on stock I have particular product, which can satisfy more requirements. The model for now is: class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Product, through='ReceiptComponent') def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) class Admin: pass def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive class Product(models.Model): name = models.CharField(max_length = 128) (...) class Admin: pass def __unicode__(self): return self.name class Stock(Store): products = models.ManyToManyField(Product) class Admin: pass def __unicode__(self): return self.name I think about making some table which joins real product (on stock) with abstract product (receiptcomponent). But maybe there's easy solution?

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  • A problem with .NET 2.0 project, using a 3.0 DLL which implements WCF services.

    - by avance70
    I made a client for accessing my WCF services in one project, and all classes that work with services inherit from this class: public abstract class ServiceClient<TServiceClient> : IDisposable where TServiceClient : ICommunicationObject This class is where I do stuff like disposing, logging when the client was called, etc. some common stuff which all service classes would normally do. Everything worked fine, until I got the task to implement this on an old system. I got into a problem when I used this project (DLL) in an other project which cannot reference System.ServiceModel (since it's an old .NET 2.0 software that I still maintain, and upgrading it to 3.0 is out of the question). Here, if I omit where TServiceClient : ICommunicationObject then the project can build, but the ServiceClient cannot use, for example, client.Close() or client.State So, is my only solution to drop the where statement, and rewrite the service classes?

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  • Vector of objects

    - by Paul
    I've got a abstract class class A { public: virtual void somefunction() = ; }; and some different classes that inherit this class: class Ab { public: void somefunction(); }; etc. I want to make a vector containing some objects of these classes (how many depends on input parameters) so I can access these easily later. However I'm a bit lost on how to do this. My best idea is vector<A> *objectsVector; Ab AbObject; objectsVector.push_back(AbObject); However this gives me a huge amout of errors from various .h files in /usr/include/c++ How should i solve this?

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  • @MustOverride annotation?

    - by Harrypotter2k5
    In .NET, one can specify a "mustoverride" attribute to a method in a particular superclass to ensure that subclasses override that particular method. I was wondering whether anybody has a custom java annotation that could achieve the same effect. Essentially what i want is to push for subclasses to override a method in a superclass that itself has some logic that must be run-through. I dont want to use abstract methods or interfaces, because i want some common functionality to be run in the super method, but more-or-less produce a compiler warning/error denoting that derivative classes should override a given method.

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  • When should one use the Abstract, Implements, or extends keywords?

    - by kdavis8
    I'm just now moving from a beginner to intermediate level android programmer in the java language. i can successfully write a game framework of classes that work together to accomplish a task beyond basic things, like hello world. but i'm having issues with some pretty basic OOP concepts; When should i derive from an abstract class? When is it more efficient to use an Interface instead of simply sub classing a parent? Basically, between extends, implements, and the abstract keywords, which keywords should be used instead of the others? i'm not looking for a basic definition, as i know them. i need to no when and why i should apply them to my code? what advantages does one have over the other? which is best for game development?

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  • is 'protected' ever reasonable outside of virtual methods and destructors?

    - by notallama
    so, suppose you have some fields and methods marked protected (non-virtual). presumably, you did this because you didn't mark them public because you don't want some nincompoop to accidentally call them in the wrong order or pass in invalid parameters, or you don't want people to rely on behaviour that you're going to change later. so, why is it okay for that nincompoop to use those fields and methods from a subclass? as far as i can tell, they can still screw up in the same ways, and the same compatibility issues still exist if you change the implementation. the cases for protected i can think of are: non-virtual destructors, so you can't break things by deleting the base class. virtual methods, so you can override 'private' methods called by the base class. constructors in c++. in java/c# marking the class as abstract will do basically the same. any other use cases?

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  • Is it okay to have many Abstract classes in your application?

    - by JoseK
    We initially wanted to implement a Strategy pattern with varying implementations of the methods in a commmon interface. These will get picked up at runtime based on user inputs. As it's turned out, we're having Abstract classes implementing 3 - 5 common methods and only one method left for a varying implementation i.e. the Strategy. Update: By many abstract classes I mean there are 6 different high level functionalities i.e. 6 packages , and each has it's Interface + AbstractImpl + (series of Actual Impl). Is this a bad design in any way? Any negative views in terms of later extensibility - I'm preparing for a code/design review with seniors.

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  • Could a singleton type replace static methods and classes?

    - by MKO
    In C# Static methods has long served a purpose allowing us to call them without instantiating classes. Only in later year have we became more aware of the problems of using static methods and classes. They can’t use interfaces They can’t use inheritance They are hard to test because you can’t make mocks and stubs Is there a better way ? Obviously we need to be able to access library methods without instantiated classes all the time otherwise our code would become pretty cluttered One possibly solution is to use a new keyword for an old concept: the singleton. Singleton’s are global instances of a class, since they are instances we can use them as we would normal classes. In order to make their use nice and practical we'd need some syntactic sugar however Say that the Math class would be of type singleton instead of an actual class. The actual class containing all the default methods for the Math singleton is DefaultMath, which implements the interface IMath. The singleton would be declared as singleton Math : IMath { public Math { this = new DefaultMath(); } } If we wanted to substitute our own class for all math operations we could make a new class MyMath that inherits DefaultMath, or we could just inherit from the interface IMath and create a whole new Class. To make our class the active Math class, you'd do a simple assignment Math = new MyMath(); and voilá! the next time we call Math.Floor it will call your method. Note that for a normal singleton we'd have to write something like Math.Instance.Floor but the compiler eliminates the need for the Instance property Another idea would be to be able to define a singletons as Lazy so they get instantiated only when they're first called, like lazy singleton Math : IMath What do you think, would it have been a better solution that static methods and classes? Is there any problems with this approach?

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  • Designing interfaces: predict methods needed, discipline yourself and deal with code that comes to m

    - by fireeyedboy
    Was: Design by contract: predict methods needed, discipline yourself and deal with code that comes to mind I like the idea of designing by contract a lot (at least, as far as I understand the principal). I believe it means you define intefaces first before you start implementing actual code, right? However, from my limited experience (3 OOP years now) I usually can't resist the urge to start coding pretty early, for several reasons: because my limited experience has shown me I am unable to predict what methods I will be needing in the interface, so I might as well start coding right away. or because I am simply too impatient to write out the whole interfaces first. or when I do try it, I still wind up implementing bits of code already, because I fear I might forget this or that imporant bit of code, that springs to mind when I am designing the interfaces. As you see, especially with the last two points, this leads to a very disorderly way of doing things. Tasks get mixed up. I should draw a clear line between designing interfaces and actual coding. If you, unlike me, are a good/disciplined planner, as intended above, how do you: ...know the majority of methods you will be needing up front so well? Especially if it's components that implement stuff you are not familiar with yet. ...resist the urge to start coding right away? ...deal with code that comes to mind when you are designing the interfaces? UPDATE: Thank you for the answers so far. Valuable insights! And... I stand corrected; it seems I misinterpreted the idea of Design By Contract. For clarity, what I actually meant was: "coming up with interface methods before implementing the actual components". An additional thing that came up in my mind is related to point 1): b) How do you know the majority of components you will be needing. How do you flesh out these things before you start actually coding? For arguments sake, let's say I'm a novice with the MVC pattern, and I wanted to implement such a component/architecture. A naive approach would be to think of: a front controller some abstract action controller some abstract view ... and be done with it, so to speak. But, being more familiar with the MVC pattern, I know now that it makes sense to also have: a request object a router a dispatcher a response object view helpers etc.. etc.. If you map this idea to some completely new component you want to develop, with which you have no experience yet; how do you come up with these sort of additional components without actually coding the thing, and stuble upon the ideas that way? How would you know up front how fine grained some components should be? Is this a matter of disciplining yourself to think it out thoroughly? Or is it a matter of being good at thinking in abstractions?

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  • I am getting this error on each machine after installing ruby and rails, I created one web site and

    - by Santodsh
    D:\PROJECTS\RubyOnRail\webapp\Welcome>ruby script\server => Booting WEBrick => Rails 2.3.4 application starting on http://0.0.0.0:3000 => Call with -d to detach => Ctrl-C to shutdown server [2010-01-31 21:19:34] INFO WEBrick 1.3.1 [2010-01-31 21:19:34] INFO ruby 1.8.6 (2007-09-24) [i386-mswin32] [2010-01-31 21:19:34] INFO WEBrick::HTTPServer#start: pid=6576 port=3000 /!\ FAILSAFE /!\ Sun Jan 31 21:19:38 +0530 2010 Status: 500 Internal Server Error uninitialized constant Encoding c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.4/lib/active_support/depend encies.rb:443:in `load_missing_constant' c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.4/lib/active_support/depend encies.rb:80:in `const_missing' c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.4/lib/active_support/depend encies.rb:92:in `const_missing' c:/ruby/lib/ruby/gems/1.8/gems/sqlite3-0.0.6/lib/sqlite3/encoding.rb:9:in `f ind' c:/ruby/lib/ruby/gems/1.8/gems/sqlite3-0.0.6/lib/sqlite3/database.rb:69:in ` initialize' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/sqlite3_adapter.rb:13:in `new' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/sqlite3_adapter.rb:13:in `sqlite3_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:223:in `send' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:223:in `new_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:245:in `checkout_new_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:188:in `checkout' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:184:in `loop' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:184:in `checkout' c:/ruby/lib/ruby/1.8/monitor.rb:242:in `synchronize' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:183:in `checkout' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:98:in `connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:326:in `retrieve_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_specification.rb:123:in `retrieve_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_specification.rb:115:in `connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/query_ca che.rb:9:in `cache' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/query_ca che.rb:28:in `call' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:361:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/head.rb:9:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/methodoverride.rb:24:in ` call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/params _parser.rb:15:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/sessio n/cookie_store.rb:93:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/failsa fe.rb:26:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `synchroniz e' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/dispat cher.rb:114:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/reload er.rb:34:in `run' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/dispat cher.rb:108:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/rails/rack/static.rb:31:in `c all' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:46:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `each' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/rails/rack/log_tailer.rb:17:i n `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/content_length.rb:13:in ` call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/handler/webrick.rb:50:in `service' c:/ruby/lib/ruby/1.8/webrick/httpserver.rb:104:in `service' c:/ruby/lib/ruby/1.8/webrick/httpserver.rb:65:in `run' c:/ruby/lib/ruby/1.8/webrick/server.rb:173:in `start_thread' c:/ruby/lib/ruby/1.8/webrick/server.rb:162:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:162:in `start_thread' c:/ruby/lib/ruby/1.8/webrick/server.rb:95:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:92:in `each' c:/ruby/lib/ruby/1.8/webrick/server.rb:92:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:23:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:82:in `start' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/handler/webrick.rb:14:in `run' c:/ruby/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/commands/server.rb:111 c:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_origina l_require' c:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' script/server:3 /!\ FAILSAFE /!\ Sun Jan 31 21:19:39 +0530 2010 Status: 500 Internal Server Error uninitialized constant Encoding c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.4/lib/active_support/depend encies.rb:443:in `load_missing_constant' c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.4/lib/active_support/depend encies.rb:80:in `const_missing' c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.4/lib/active_support/depend encies.rb:92:in `const_missing' c:/ruby/lib/ruby/gems/1.8/gems/sqlite3-0.0.6/lib/sqlite3/encoding.rb:9:in `f ind' c:/ruby/lib/ruby/gems/1.8/gems/sqlite3-0.0.6/lib/sqlite3/database.rb:69:in ` initialize' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/sqlite3_adapter.rb:13:in `new' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/sqlite3_adapter.rb:13:in `sqlite3_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:223:in `send' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:223:in `new_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:245:in `checkout_new_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:188:in `checkout' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:184:in `loop' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:184:in `checkout' c:/ruby/lib/ruby/1.8/monitor.rb:242:in `synchronize' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:183:in `checkout' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:98:in `connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:326:in `retrieve_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_specification.rb:123:in `retrieve_connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_specification.rb:115:in `connection' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/query_ca che.rb:9:in `cache' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/query_ca che.rb:28:in `call' c:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connecti on_adapters/abstract/connection_pool.rb:361:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/head.rb:9:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/methodoverride.rb:24:in ` call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/params _parser.rb:15:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/sessio n/cookie_store.rb:93:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/failsa fe.rb:26:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `synchroniz e' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/dispat cher.rb:114:in `call' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/reload er.rb:34:in `run' c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/action_controller/dispat cher.rb:108:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/rails/rack/static.rb:31:in `c all' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:46:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `each' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `call' c:/ruby/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/rails/rack/log_tailer.rb:17:i n `call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/content_length.rb:13:in ` call' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/handler/webrick.rb:50:in `service' c:/ruby/lib/ruby/1.8/webrick/httpserver.rb:104:in `service' c:/ruby/lib/ruby/1.8/webrick/httpserver.rb:65:in `run' c:/ruby/lib/ruby/1.8/webrick/server.rb:173:in `start_thread' c:/ruby/lib/ruby/1.8/webrick/server.rb:162:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:162:in `start_thread' c:/ruby/lib/ruby/1.8/webrick/server.rb:95:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:92:in `each' c:/ruby/lib/ruby/1.8/webrick/server.rb:92:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:23:in `start' c:/ruby/lib/ruby/1.8/webrick/server.rb:82:in `start' c:/ruby/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/handler/webrick.rb:14:in `run' c:/ruby/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/commands/server.rb:111 c:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_origina l_require' c:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' script/server:3

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  • java : how to handle the design when template methods throw exception when overrided method not throw

    - by jiafu
    when coding. try to solve the puzzle: how to design the class/methods when InputStreamDigestComputor throw IOException? It seems we can't use this degisn structure due to the template method throw exception but overrided method not throw it. but if change the overrided method to throw it, will cause other subclass both throw it. So can any good suggestion for this case? abstract class DigestComputor{ String compute(DigestAlgorithm algorithm){ MessageDigest instance; try { instance = MessageDigest.getInstance(algorithm.toString()); updateMessageDigest(instance); return hex(instance.digest()); } catch (NoSuchAlgorithmException e) { LOG.error(e.getMessage(), e); throw new UnsupportedOperationException(e.getMessage(), e); } } abstract void updateMessageDigest(MessageDigest instance); } class ByteBufferDigestComputor extends DigestComputor{ private final ByteBuffer byteBuffer; public ByteBufferDigestComputor(ByteBuffer byteBuffer) { super(); this.byteBuffer = byteBuffer; } @Override void updateMessageDigest(MessageDigest instance) { instance.update(byteBuffer); } } class InputStreamDigestComputor extends DigestComputor{ // this place has error. due to exception. if I change the overrided method to throw it. evey caller will handle the exception. but @Override void updateMessageDigest(MessageDigest instance) { throw new IOException(); } }

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  • Should I use a collection here?

    - by Eva
    So I have code set up like this: public interface IInterface { public void setField(Object field); } public abstract class AbstractClass extends JPanel implements IInterface { private Object field_; public void setField(Object field) { field_ = field; } } public class ClassA extends AbstractClass { public ClassA() { // unique ClassA constructor stuff } public Dimension getPreferredSize() { return new Dimension(1, 1); } } public class ClassB extends AbstractClass { public ClassB() { // unique ClassB constructor stuff } public Dimension getPreferredSize() { return new Dimension(42, 42); } } public class ConsumerA { public ConsumerA(Collection<AbstractClass> collection) { for (AbstractClass abstractClass : collection) { abstractClass.setField(this); abstractClass.repaint(); } } } All hunky-dory so far, until public class ConsumerB { // Option 1 public ConsumerB(ClassA a, ClassB b) { methodThatOnlyTakesA(a); methodThatOnlyTakesB(b); } // Option 2 public ConsumerB(Collection<AbstractClass> collection) { for (IInterface i : collection) { if (i instanceof ClassA) { methodThatOnlyTakesA((ClassA) i); else if (i instanceof ClassB) { methodThatOnlyTakesB((ClassB) i); } } } } public class UsingOption1 { public static void main(String[] args) { ClassA a = new ClassA(); ClassB b = new ClassB(); Collection<AbstractClass> collection = Arrays.asList(a, b); ConsumerA consumerA = new ConsumerA(collection); ConsumerB consumerB = new ConsumerB(a, b); } } public class UsingOption2 { public static void main(String[] args) { Collection<AbstractClass> collection = Arrays.asList(new ClassA(), new ClassB()); ConsumerA = new ConsumerA(collection); ConsumerB = new ConsumerB(collection); } } With a lot more classes extending AbstractClass, both options get unwieldly. Option1 would make the constructor of ConsumerB really long. Also UsingOption1 would get long too. Option2 would have way more if statements than I feel comfortable with. Is there a viable Option3? If it helps, ClassA and ClassB have all the same methods, they're just implemented differently. Thanks for slogging through my code!

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  • Email function using templates. Includes via ob_start and global vars

    - by Geo
    I have a simple Email() class. It's used to send out emails from my website. <? Email::send($to, $subj, $msg, $options); ?> I also have a bunch of email templates written in plain HTML pierced with a few PHP variables. E.g. /inc/email/templates/account_created.php: <p>Dear <?=$name?>,</p> <p>Thank you for creating an account at <?=$SITE_NAME?>. To login use the link below:</p> <p><a href="https://<?=$SITE_URL?>/account" target="_blank"><?=$SITE_NAME?>/account</a></p> In order to have the PHP vars rendered I had to include the template into my function. But since include does not return the contents but rather just sends it directly to the output, I had to wrap it with the buffer functions: <? abstract class Email { public static function send($to, $subj, $msg, $options = array()) { /* ... */ ob_start(); include '/inc/email/templates/account_created.php'; $msg = ob_get_clean(); /* ... */ } } After that I realized that the PHP vars are not rendered as they are being inside of the function scope, so I had to globalize the variables inside of the template: <? global $SITE_NAME, $SITE_URL, $name; ?> <p>Dear <?=$name?>,</p> ... So the question is whether there is a more elegant solution to this? Mainly I am concerned about my workarounds using ob_start() and global. For some reason that seems to me odd. Or this is pretty much the common practice?

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  • When do instance variables get initialized and values assigned?

    - by AKh
    When doees the instance variable get initialized? Is it after the constructor block is done or before it? Consider this example: public abstract class Parent { public Parent(){ System.out.println("Parent Constructor"); init(); } public void init(){ System.out.println("parent Init()"); } } public class Child extends Parent { private Integer attribute1; private Integer attribute2 = null; public Child(){ super(); System.out.println("Child Constructor"); } public void init(){ System.out.println("Child init()"); super.init(); attribute1 = new Integer(100); attribute2 = new Integer(200); } public void print(){ System.out.println("attribute 1 : " +attribute1); System.out.println("attribute 2 : " +attribute2); } } public class Tester { public static void main(String[] args) { Parent c = new Child(); ((Child)c).print(); } } OUTPUT: Parent Constructor Child init() parent Init() Child Constructor attribute 1 : 100 attribute 2 : null When the memory for the atribute 1 & 2 are allocated in the heap ? Curious to know why is attribute 2 is NULL ? Are there any design flaws?

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  • Linking a template class using another template class (error LNK2001)

    - by Luís Guilherme
    I implemented the "Strategy" design pattern using an Abstract template class, and two subclasses. Goes like this: template <class T> class Neighbourhood { public: virtual void alter(std::vector<T>& array, int i1, int i2) = 0; }; and template <class T> class Swap : public Neighbourhood<T> { public: virtual void alter(std::vector<T>& array, int i1, int i2); }; There's another subclass, just like this one, and alter is implemented in the cpp file. Ok, fine! Now I declare another method, in another class (including neighbourhood header file, of course), like this: void lSearch(/*parameters*/, Neighbourhood<LotSolutionInformation> nhood); It compiles fine and cleanly. When starting to link, I get the following error: 1>SolverFV.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall lsc::Neighbourhood<class LotSolutionInformation>::alter(class std::vector<class LotSolutionInformation,class std::allocator<class LotSolutionInformation> > &,int,int)" (?alter@?$Neighbourhood@VLotSolutionInformation@@@lsc@@UAEXAAV?$vector@VLotSolutionInformation@@V?$allocator@VLotSolutionInformation@@@std@@@std@@HH@Z)

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  • Injecting correct object graph using StructureMap in Queue of different Objects

    - by davy
    I have a queuing service that has to inject a different dependency graph depending on the type of object in the queue. I'm using Structure Map. So, if the object in the queue is TypeA the concrete classes for TypeA are used and if it's TypeB, the concrete classes for TypeB are used. I'd like to avoid code in the queue like: if (typeA) { // setup TypeA graph } else if (typeB) { // setup TypeB graph } Within the graph, I also have a generic classes such as an IReader(ISomething, ISpomethingElse) where IReader is generic but needs to inject the correct ISomething and ISomethingElse for the type. ISomething will also have dependencies and so on. Currently I create a TypeA or TypeB object and inject a generic Processor class using StructureMap into it and then pass a factory manually inject a TypeA or TypeB factory into a method like: Processor.Process(new TypeAFactory) // perhaps I should have an abstract factory... However, because the factory then creates the generic IReader mentioned above, I end up manually injecting all the TypeA or TypeB classes fro there on. I hope enough of this makes sense. I am new to StructureMap and was hoping somebody could point me in the right direction here for a flexible and elegant solution. Thanks

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  • Should I Teach My Son Programming? What approaches should I take? [closed]

    - by DaveDev
    I was wondering if it's a good idea to teach object oriented programming to my son? I was never really good at math as a kid, but I think since I've started programming it's given me a greater ability to understand math by being better able to visualise relationships between abstract models. I thought it might give him a better advantage in learning & applying logical & mathematical concepts throughout his life if he was able to take advantage of the tools available to programmers. what would be the best programming fields, techniques and/or concepts? What approach should I take? what concepts should I avoid? what fields of mathematics would he find this benfits him most? He's only 2 now so it wouldn't be for another few years before I do this, (and even at that, only from a very high level point of view). I thought I'd put it to the programming community and see what you guys thought? Possible Duplicate: What are some recommended programming resources for pre-teens?

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  • iPhone SDK: selectRowAtIndexPath with delegate methods

    - by norskben
    Hi SO I am using selectRowAtIndexPath to select a tableview in the same ViewController class, but this does not run the delegate methods, eg: tableView:didSelectRowAtIndexPath I would like these delegate methods to also be called. Is there another API call I can be using? Thanks From the apple docs: selectRowAtIndexPath:animated:scrollPosition: Selects a row in the receiver identified by index path, optionally scrolling the row to a location in the receiver. - (void)selectRowAtIndexPath:(NSIndexPath *)indexPath animated:(BOOL)animated scrollPosition:(UITableViewScrollPosition)scrollPosition Calling this method does not cause the delegate to receive a tableView:willSelectRowAtIndexPath: or tableView:didSelectRowAtIndexPath: message, nor will it send UITableViewSelectionDidChangeNotification notifications to observers.

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  • NSFetchedResultsController - Delegate methods crashing under iPhone OS 3.0, but NOT UNDER 3.1

    - by Scott Langendyk
    Hey guys, so I've got my NSFetchedResultsController working fine under the 3.1 SDK, however I start getting some weird errors, specifically in the delegate methods when I try it under 3.0. I've determined that this is related to the NSFetchedResultsControllerDelegate methods. This is what I have set up. The inEditingMode stuff has to do with the way I've implemented adding another static section to the table. - (void)controllerWillChangeContent:(NSFetchedResultsController*)controller { [self.tableView beginUpdates]; } - (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type{ NSIndexSet *sectionSet = [NSIndexSet indexSetWithIndex:sectionIndex]; if(self.inEditingMode){ sectionSet = [NSIndexSet indexSetWithIndex:sectionIndex + 1]; } switch (type) { case NSFetchedResultsChangeInsert: [self.tableView insertSections:sectionSet withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [self.tableView deleteSections:sectionSet withRowAnimation:UITableViewRowAnimationFade]; break; default: [self.tableView reloadData]; break; } } - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath{ NSIndexPath *relativeIndexPath = indexPath; NSIndexPath *relativeNewIndexPath = newIndexPath; if(self.inEditingMode){ relativeIndexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:indexPath.section + 1]; relativeNewIndexPath = [NSIndexPath indexPathForRow:newIndexPath.row inSection:newIndexPath.section + 1]; } switch(type) { case NSFetchedResultsChangeInsert: [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:relativeNewIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:relativeIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; default: [self.tableView reloadData]; break; } } -(void)controllerDidChangeContent:(NSFetchedResultsController *)controller{ [self.tableView endUpdates]; } When I add an entity to the managed object context, I get the following error: Serious application error. Exception was caught during Core Data change processing: *** -[NSCFArray objectAtIndex:]: index (1) beyond bounds (1) with userInfo (null) I put a breakpoint on objc_exception_throw, and the crash seems to be occuring inside of controllerDidChangeContent. If I comment out all of the self.tableView methods, and put a single [self.tableView reloadData] inside of controllerDidChangeContent, everything works as expected. Anybody have any idea as to why this is happening?

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  • MVC - Calling Controller Methods

    - by JT703
    Hello, My application is following the MVC design pattern. The problem I keep running into is needing to call methods inside a Controller class from outside that Controller class (ex. A View class wants to call a Controller method, or a Manager class wants to call a Controller method). Is calling Controller methods in this way allowed in MVC? If it's allowed, what's the proper way to do it? According to the version of MVC that I am following (there seems to be so many different versions out there), the View knows of the Model, and the Controller knows of the View. Doing it this way, I can't access the controller. Here's the best site I've found and the one describing the version of MVC I'm following: http://leepoint.net/notes-java/GUI/structure/40mvc.html. The Main Program code block really shows how this works. Thanks for any answers.

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  • jQuery plug-in with additional methods.

    - by Kieron
    I've a jQuery plug-in that operates on some ULs, adding and removing classes etc. During the life-cycle of the page, I'll need to add/ remove some classes in code, and as my plug-in needs to perform some additional operations when this happens I came up with the following: // This is the initialiser method... $.fn.objectBuilder = function (options) {...}; // These are the two new methods I need. $.fn.objectBuilder.setSelected(element) {...}; $.fn.objectBuilder.removeSelected() {...}; I'd then like to call them like this: $("#ob1").objectbuilder.removeSelected(); Any thoughts? Thanks, Kieron edit I suppose what I'm asking is, whats the best way of adding additional methods to a jQuery plug-in where it'll have access to the root object, in this case #obj when the method is called.

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  • UIViewController not oreintating. Methods not called

    - by capple
    Greetings, This question does seem to be an ongoing saga in the world of iphone SDK... so heres my contribution... Had two separate projects from the same template... one semi-works, the other not at all... Please let me explain my steps... used this basic GL ES template //iphonedevelopment.blogspot.com/2008/12/opengl-project-template-for-xcode.html had to sort out some of the 'Release' configuration but otherwises has eveything I need to add orientation to a GL ES project. One my first project, did my stuff, then added these methods.... -(BOOL)shouldAutoRotateToInterfaceOrientation ..... -(void)willRotateToInterfaceOrientation .... -(void)didRotateFromInterfaceOrientation .... -(void)willAnimateRotationToInterfaceOrientation .... And understand what they do (or are trying to do in my case), the (BOOL)should... gets called once when the view controller is created, and returns 'YES'. But after that none of the other methods are called! So I started from scratch with a blank template (GL ES one from above)...and added minimum to support auto rotation. But this time none of the methods get called! So I investigated .... //developer.apple.com/iphone/library/qa/qa2010/qa1688.html as it said, I added the GLViewController.view first, then added the GLview as subviews of the application delegate. Nothing! Then found this //www.iphonedevsdk.com/forum/iphone-sdk-development/44993-how-determine-ipad-launch-orientation.html which states to enable orientation notifications [[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications]; and then subsequently disable them in the view controller... makes sense...did it, nothing... I think the notifications might be on by default though, since I didn't need to enable them in the first project, yet it still try to verify a orientation (i.e (BOOL)shouldAutoRotate... )... If any one could help me out it would be greatly appreciated as this issue is driving me insane. Thanks in advance. The code can be found here ... http://rapidshare.com/files/392053688/autoRotation.zip N.B These projects avoid nib/xib resources, would like to keep it that way if possible. P.S iPad device not out where I am so I cannot test on a device yet. Would be nice for it to work on the simulator.

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  • Passing methods/functions as args in Objective C

    - by Baishampayan Ghose
    Hello, I am new to Objective C and I am trying to implement an async library which works with callbacks. I need to figure out a way to pass callback methods as args to my async methods so that the callback can be invoked when the task is finished. What is the best way to achieve this in Objective C? In Python, for example I could easily pass a function, but in Objective C it seems selectors are the way to go(?). Can anyone point me to an example from where I can get some ideas? Thanks in advance.

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