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• WCF ChannelFactory caching

  - by Myles J

  I've just read this great article on WCF ChannelFactory caching by Wenlong Dong. My question is simply how can you actually prove that the ChannelFactory is in fact being cached between calls? I've followed the rules regarding the ClientBase’s constructors. We are using the following overloaded constructor on our object that inherits from ClientBase: ClientBase(string endpointConfigurationName, EndpointAddress remoteAddress); In the article mentioned above it is stated that: For these constructors, all arguments (including default ones) are in the following list: · InstanceContext callbackInstance · string endpointConfigurationName · EndpointAddress remoteAddress As long as these three arguments are the same when ClientBase is constructed, we can safely assume that the same ChannelFactory can be used. Fortunately, String and EndpointAddress types are immutable, i.e., we can make simple comparison to determine whether two arguments are the same. For InstanceContext, we can use Object reference comparison. The type EndpointTrait is thus used as the key of the MRU cache. To test the ChannelFactory cache theory we are checking the Hashcode in the ClientBase constructor e.g. var testHash = RuntimeHelpers.GetHashCode(base.ChannelFactory); The hash value is different between calls which makes us think that the ChannelFactory isn't actually cached. Any thoughts? Regards Myles

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• In Java Concurrency In Practice by Brian Goetz, why is the Memoizer class not annotated with @ThreadSafe?

  - by dig_dug

  Java Concurrency In Practice by Brian Goetz provides an example of a efficient scalable cache for concurrent use. The final version of the example showing the implementation for class Memoizer (pg 108) shows such a cache. I am wondering why the class is not annotated with @ThreadSafe? The client, class Factorizer, of the cache is properly annotated with @ThreadSafe. The appendix states that if a class is not annotated with either @ThreadSafe or @Immutable that it should be assumed that it isn't thread safe. Memoizer seems thread-safe though. Here is the code for Memoizer: public class Memoizer<A, V> implements Computable<A, V> { private final ConcurrentMap<A, Future<V>> cache = new ConcurrentHashMap<A, Future<V>>(); private final Computable<A, V> c; public Memoizer(Computable<A, V> c) { this.c = c; } public V compute(final A arg) throws InterruptedException { while (true) { Future<V> f = cache.get(arg); if (f == null) { Callable<V> eval = new Callable<V>() { public V call() throws InterruptedException { return c.compute(arg); } }; FutureTask<V> ft = new FutureTask<V>(eval); f = cache.putIfAbsent(arg, ft); if (f == null) { f = ft; ft.run(); } } try { return f.get(); } catch (CancellationException e) { cache.remove(arg, f); } catch (ExecutionException e) { throw launderThrowable(e.getCause()); } } } }

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• what's the alternative to readonlycollection when using lazy="extra"?

  - by Kunjan

  I am trying to use lazy="extra" for the child collection of Trades I have on my Client object. The trades is an Iset<Trade Trades, exposed as ReadOnlyCollection<Trade because I do not want anyone to modify the collection directly. As a result, I have added AddTrade and RemoveTrade methods. Now I have a Client Search page where I need to show the Trade Count. and on the Client details page I have a tab where I need to show all the trades for the Client in paged gridview. What I want to achieve is, for the search when I say on the client object as client.Trades.Count, nHibernate should only fire a select count(*) query. Hence I am using lazy="extra". But because I am using a ReadOnlyCollection, nHibernate fires a count query & a separate query to load the child collection trades completely. Also, I cannot include the Trades in my initial search request as this would disturb the paging because a counterparty can have n trades which would result in n rows, when I am searching clients only. So the child collections have to be loaded lazily. The second problem is that on the client details page -- Trades grid view, I have enabled paging for performance reasons. But by nature nHibernate loads the entire collection of trades as the user goes from one page to another. Ideally I want to control this by getting only trades specific to the page the user is on. How can I achieve this? I came across this very good article. http://stackoverflow.com/questions/876976/implementing-ipagedlistt-on-my-models-using-nhibernate But I am not sure if this will work for me, as lazy=extra currently doesnt work as expected with the ReadOnlyCollection. So, if I went ahead and implemented the solution this way and further enhanced it by making the List/Set Immutable, will lazy=extra give me the same problem as with ReadOnlyCollections?

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• Invoice & Invoice lines: How do you store customer address information?

  - by elviejo

  Hi I'm developing an invoicing application. So the general idea is to have two tables: Invoice (ID, Date, CustomerAddress, CustomerState, CustomerCountry, VAT, Total); InvoiceLine (Invoice_ID, ID, Concept, Units, PricePerUnit, Total); As you can see this basic design leads to a lot of repetiton of records where the client will have the same addrres, state and country. So the alternative is to have an address table and then make a relationship Address<-Invoice. However I think that an invoice is immutable document and should be stored just the way it was first made. Sometimes customers change their addresses, or states and if it was coming from an Address catalog that will change all the previously made invoices. So What is your experience? How is the customer address stored in an invoice? In the Invoice table? an Address Table? or something else? Can you provide pointers to a book, article or document where this is discussed in further detail?

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• Django forms, inheritance and order of form fields

  - by Hannson

  I'm using Django forms in my website and would like to control the order of the fields. Here's how I define my forms: class edit_form(forms.Form): summary = forms.CharField() description = forms.CharField(widget=forms.TextArea) class create_form(edit_form): name = forms.CharField() The name is immutable and should only be listed when the entity is created. I use inheritance to add consistency and DRY principles. What happens which is not erroneous, in fact totally expected, is that the name field is listed last in the view/html but I'd like the name field to be on top of summary and description. I do realize that I could easily fix it by copying summary and description into create_form and loose the inheritance but I'd like to know if this is possible. Why? Imagine you've got 100 fields in edit_form and have to add 10 fields on the top in create_form - copying and maintaining the two forms wouldn't look so sexy then. (This is not my case, I'm just making up an example) So, how can I override this behavior? Edit: Apparently there's no proper way to do this without going through nasty hacks (fiddling with .field attribute). The .field attribute is a SortedDict (one of Django's internal datastructures) which doesn't provide any way to reorder key:value pairs. It does how-ever provide a way to insert items at a given index but that would move the items from the class members and into the constructor. This method would work, but make the code less readable. The only other way I see fit is to modify the framework itself which is less-than-optimal in most situations. In short the code would become something like this: class edit_form(forms.Form): summary = forms.CharField() description = forms.CharField(widget=forms.TextArea) class create_form(edit_form): def __init__(self,*args,**kwargs): forms.Form.__init__(self,*args,**kwargs) self.fields.insert(0,'name',forms.CharField()) That shut me up :)

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• Nested multithread operations tracing

  - by Sinix

  I've a code alike void ExecuteTraced(Action a, string message) { TraceOpStart(message); a(); TraceOpEnd(message); } The callback (a) could call ExecuteTraced again, and, in some cases, asynchronously (via ThreadPool, BeginInvoke, PLINQ etc, so I've no ability to explicitly mark operation scope). I want to trace all operation nested (even if they perform asynchronously). So, I need the ability to get last traced operation inside logical call context (there may be a lot of concurrent threads, so it's impossible to use lastTraced static field). There're CallContext.LogicalGetData and CallContext.LogicalSetData, but unfortunately, LogicalCallContext propagates changes back to the parent context as EndInvoke() called. Even worse, this may occure at any moment if EndInvoke() was called async. http://stackoverflow.com/questions/883486/endinvoke-changes-current-callcontext-why Also, there is Trace.CorrelationManager, but it based on CallContext and have all the same troubles. There's a workaround: use the CallContext.HostContext property which does not propagates back as async operation ended. Also, it does'nt clone, so the value should be immutable - not a problem. Though, it's used by HttpContext and so, workaround is not usable in Asp.Net apps. The only way I see is to wrap HostContext (if not mine) or entire LogicalCallContext into dynamic and dispatch all calls beside last traced operation. Help, please!

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• Safe to update separate regions of a BufferedImage in separate threads?

  - by finnw

  I have a collection of BufferedImage instances, one main image and some subimages created by calling getSubImage on the main image. The subimages do not overlap. I am also making modifications to the subimage and I want to split this into multiple threads, one per subimage. From my understanding of how BufferedImage, Raster and DataBuffer work, this should be safe because: Each instance of BufferedImage (and its respective WritableRaster) is accessed from only one thread. The shared ColorModel is immutable The DataBuffer has no fields that can be modified (the only thing that can change is elements of the backing array.) Modifying disjoint segments of an array in separate threads is safe. However I cannot find anything in the documentation that says that it is definitely safe to do this. Can I assume it is safe? I know that it is possible to work on copies of the child Rasters but I would prefer to avoid this because of memory constraints. Otherwise, is it possible to make the operation thread-safe without copying regions of the parent image?

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• Types issue in F#

  - by Andry

  Hello! In my ongoing adventure deep diving into f# I am understanding a lot of this powerful language but there are things that I still do not understand so clearly. One of the most important issues I need to master is types. Well the book I am reading is very straight forward and introduces entities and main functionalities with a direct approach. The first thing I could get start with is types. It introduces the main types as list, option, tuples, and so on... It is clearly underlined that all these types are IMMUTABLE for many reasons regarding functional programming and data consistance in functional programing. Well, no problems until now... But now I am getting started with Concrete Types... Well... I have problems in managing with types like list, option, tuples, types created through new operator and concrete types created using type keyword (for abbreviations, concrete types...). So my question is: how can I efficently catalogue/distinguish all types of data in f#???? I can create a perfect separation among types in C#, VB.NET... FOr example in VB.NET there are value and reference types while in C# there are only references and also int, double are treated as objects (they are objects while in VB.NET a value type is not a object and there is a split in types for this reason). Well in F# I cannot create such differences among types in the language. Can you help me? I hope I was clear.

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• Design suggestion for expression tree evaluation with time-series data

  - by Lirik

  I have a (C#) genetic program that uses financial time-series data and it's currently working but I want to re-design the architecture to be more robust. My main goals are: sequentially present the time-series data to the expression trees. allow expression trees to access previous data rows when needed. to optimize performance of the data access while evaluating the expression trees. keep a common interface so various types of data can be used. Here are the possible approaches I've thought about: I can evaluate the expression tree by passing in a data row into the root node and let each child node use the same data row. I can evaluate the expression tree by passing in the data row index and letting each node get the data row from a shared DataSet (currently I'm passing the row index and going to multiple synchronized arrays to get the data). Hybrid: an immutable data set is accessible by all of the expression trees and each expression tree is evaluated by passing in a data row. The benefit of the first approach is that the data row is being passed into the expression tree and there is no further query done on the data set (which should increase performance in a multithreaded environment). The drawback is that the expression tree does not have access to the rest of the data (in case some of the functions need to do calculations using previous data rows). The benefit of the second approach is that the expression trees can access any data up to the latest data row, but unless I specify what that row is, I'll have to iterate through the rows and figure out which one is the last one. The benefit of the hybrid is that it should generally perform better and still provide access to the earlier data. It supports two basic "views" of data: the latest row and the previous rows. Do you guys know of any design patterns or do you have any tips that can help me build this type of system? Should I use a DataSet to hold and present the data, or are there more efficient ways to present rows of data while maintaining a simple interface? FYI: All of my code is written in C#.

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• Java: Is clone() really ever used? What about defensive copying in getters/setters?

  - by GreenieMeanie

  Do people practically ever use defensive getters/setters? To me, 99% of the time you intend for the object you set in another object to be a copy of the same object reference, and you intend for changes you make to it to also be made in the object it was set in. If you setDate(Date dt) and modify dt later, who cares? Unless I want some basic immutable data bean that just has primitives and maybe something simple like a Date, I never use it. As far as clone, there are issues as to how deep or shallow the copy is, so it seems kind of "dangerous" to know what is going to come out when you clone an Object. I think I have only used clone() once or twice, and that was to copy the current state of the object because another thread (ie another HTTP request accessing the same object in Session) could be modifying it. Edit - A comment I made below is more the question: But then again, you DID change the Date, so it's kind of your own fault, hence whole discussion of term "defensive". If it is all application code under your own control among a small to medium group of developers, will just documenting your classes suffice as an alternative to making object copies? Or is this not necessary, since you should always assume something ISN'T copied when calling a setter/getter?

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• How to associate static entity instances in a Session without database retrieval

  - by Michael Hedgpeth

  I have a simple Result class that used to be an Enum but has evolved into being its own class with its own table. public class Result { public static readonly Result Passed = new Result(StatusType.Passed) { Id = [Predefined] }; public static readonly Result NotRun = new Result(StatusType.NotRun) { Id = [Predefined] }; public static readonly Result Running = new Result(StatusType.Running) { Id = [Predefined] }; } Each of these predefined values has a row in the database at their predefined Guid Id. There is then a failed result that has an instance per failure: public class FailedResult : Result { public FailedResult(string description) : base(StatusType.Failed) { . . . } } I then have an entity that has a Result: public class Task { public Result Result { get; set; } } When I save a Task, if the Result is a predefined one, I want NHibernate to know that it doesn't need to save that to the database, nor does it need to fetch it from the database; I just want it to save by Id. The way I get around this is when I am setting up the session, I call a method to load the static entities: protected override void OnSessionOpened(ISession session) { LockStaticResults(session, Result.Passed, Result.NotRun, Result.Running); } private static void LockStaticResults(ISession session, params Result[] results) { foreach (var result in results) { session.Load(result, result.Id); } } The problem with the session.Load method call is it appears to be fetching to the database (something I don't want to do). How could I make this so it does not fetch the database, but trusts that my static (immutable) Result instances are both up to date and a part of the session?

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• Applying for .net jobs as a "self learner"

  - by DeanMc

  Hi All, I have recently started applying for .Net jobs. I currently work in a sales role with a large telco. I found out quite late that I like programming and as such bought my house and made commitments that mean college is not an option. What I would like to know is, is it harder to get a junior job as a self learner? I have gotten a few enquiries regarding my C.V but nothing concrete yet. I try to be involved in projects as I get the chance and tend to put up any worthwhile projects as I develop them. Some examples of my work are: A Xaml lexer and parser: http://www.xlight.mendhak.com A font obfuscation tool: http://www.silverlightforums.com/showthread.php?1516-Font-Obsfucation-Tool-ALPHA A tagger for m4a: http://projectaudiophile.codeplex.com/SourceControl/list/changesets I, of course think that these are great examples of my work but that is my opinion based on self learning. The other query is how much should I actually know? I've never used linked lists but I know that strings are immutable and I understand what that means. I am only touching on T-SQL but I understand things like how properties function in IL (as two standard methods :) ). I suppose I understand a lot of concepts but specific features need some looking up to implement as I may not know the syntax off the top of my head.

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• How should I avoid memoization causing bugs in Ruby?

  - by Andrew Grimm

  Is there a consensus on how to avoid memoization causing bugs due to mutable state? In this example, a cached result had its state mutated, and therefore gave the wrong result the second time it was called. class Greeter def initialize @greeting_cache = {} end def expensive_greeting_calculation(formality) case formality when :casual then "Hi" when :formal then "Hello" end end def greeting(formality) unless @greeting_cache.has_key?(formality) @greeting_cache[formality] = expensive_greeting_calculation(formality) end @greeting_cache[formality] end end def memoization_mutator greeter = Greeter.new first_person = "Bob" # Mildly contrived in this case, # but you could encounter this in more complex scenarios puts(greeter.greeting(:casual) << " " << first_person) # => Hi Bob second_person = "Sue" puts(greeter.greeting(:casual) << " " << second_person) # => Hi Bob Sue end memoization_mutator Approaches I can see to avoid this are: greeting could return a dup or clone of @greeting_cache[formality] greeting could freeze the result of @greeting_cache[formality]. That'd cause an exception to be raised when memoization_mutator appends strings to it. Check all code that uses the result of greeting to ensure none of it does any mutating of the string. Is there a consensus on the best approach? Is the only disadvantage of doing (1) or (2) decreased performance? (I also suspect freezing an object may not work fully if it has references to other objects) Side note: this problem doesn't affect the main application of memoization: as Fixnums are immutable, calculating Fibonacci sequences doesn't have problems with mutable state. :)

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• Looking for detailed explanation of Hibernate UserType methods for mutable objects

  - by Tom

  I am creating a custom UserType class in Hibernate. The specific case is for an HL7v3 clinical document (I work in health IT). It is a mutable object and most of the documentation around the Hibernate UserType interface seems to center around immutable types. I want a better understanding of how and when the interface methods are used, specifically: assemble - why two parameters (one Serializable, one Object)? What is the use case for this method? disassemble - should I just implement this method to return a serializable form (e.g. String representation)? When and how is this method invoked? equals - is this for update? read? contention? dirty reads? What are the consequences of simply returning false in most cases? replace - I really don't understand where the three Object parameters come from, when this method is invoked, and what Hibernate expects to return, or how that return value is used. Any pointers would be appreciated. I've searched and read all I can find on the subject, but have not found much documentation at all explaining how these methods are used for mutable objects.

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• Partially constructed object / Multi threading

  - by reto

  Heya! I'm using joda due to it's good reputation regarding multi threading. It goes great distances to make multi threaded date handling efficient, for example by making all Date/Time/DateTime objects immutable. But here's a situation where I'm not sure if Joda is really doing the right thing. It probably is correct, but I'd be very interested to see the explanation for it. When a toString() of a DateTime is being called Joda does the following: /* org.joda.time.base.AbstractInstant */ public String toString() { return ISODateTimeFormat.dateTime().print(this); } All formatters are thread safe, as they are as well ready-only. But what's about the formatter-factory: private static DateTimeFormatter dt; /* org.joda.time.format.ISODateTimeFormat */ public static DateTimeFormatter dateTime() { if (dt == null) { dt = new DateTimeFormatterBuilder() .append(date()) .append(tTime()) .toFormatter(); } return dt; } This is a common pattern in single threaded applications. I see the following dangers: Race condition during null check -- worst case: two objects get created. No Problem, as this is solely a helper object (unlike a normal singleton pattern situation), one gets saved in dt, the other is lost and will be garbage collected sooner or later. the static variable might point to a partially constructed object before the objec has been finished initialization (before calling me crazy, read about a similar situation in this Wikipedia article. So how does Joda ensure that not partially created formatter gets published in this static variable? Thanks for your explanations! Reto

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• Using Scala and StringTemplate, how do I loop through a Map

  - by Marcus Kazmierczak

  I have my environment setup nicely using Scala, StringTempalte within the Google AppEngine. I am having trouble looping through a Map and getting it to display in the template. When I assign a simple List of just Strings to the template it works using: In Scala Servlet: var photos = List[String]() //... get photo url and title ... photos = photo_url :: photos template.setAttribute("photos", photos: _*) In Template: $photos: { photo| <div><img src="$photo$_s.jpg"></div> }$ The above works. However, any attempt of creating a Map using url and title and assigning to the template gives me an error. Here is my attempt, which does not work: In Scala Servlet: var photos = List[Map[String,String]]() //... get photo url and title ... photos = Map("url" -> url, "title" -> title) :: photos template.setAttribute("photos", photos: _*) In Template: $photos: { photo| <div><img src="$photo.url$_s.jpg" title="$photo.title$"></div> }$ This gives me the following error Class scala.collection.immutable.Map$Map2 has no such attribute: title in template context Thoughts / Ideas ?

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• Database Functional Programming in Clojure

  - by Ralph

  "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow I need to write a tool to dump a large hierarchical (SQL) database to XML. The hierarchy consists of a Person table with subsidiary Address, Phone, etc. tables. I have to dump thousands of rows, so I would like to do so incrementally and not keep the whole XML file in memory. I would like to isolate non-pure function code to a small portion of the application. I am thinking that this might be a good opportunity to explore FP and concurrency in Clojure. I can also show the benefits of immutable data and multi-core utilization to my skeptical co-workers. I'm not sure how the overall architecture of the application should be. I am thinking that I can use an impure function to retrieve the database rows and return a lazy sequence that can then be processed by a pure function that returns an XML fragment. For each Person row, I can create a Future and have several processed in parallel (the output order does not matter). As each Person is processed, the task will retrieve the appropriate rows from the Address, Phone, etc. tables and generate the nested XML. I can use a a generic function to process most of the tables, relying on database meta-data to get the column information, with special functions for the few tables that need custom processing. These functions could be listed in a map(table name -> function). Am I going about this in the right way? I can easily fall back to doing it in OO using Java, but that would be no fun. BTW, are there any good books on FP patterns or architecture? I have several good books on Clojure, Scala, and F#, but although each covers the language well, none look at the "big picture" of function programming design.

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• Tips on designing a .NET API for future use with F#

  - by Drew Noakes

  I'm in the process of designing a .NET API to allow developers to create RoboCup agents for the 3D simulated soccer league. I'm pretty happy with how the API work with C# code, however I would like to use this project to improve my F# skill (which is currently based on reading rather than practice). So I would like to ask what kinds of things I should consider when designing an API that is to be consumed by both C# and F# code. Some points. I make fairly heavy use of matrix and vector math. These are currently immutable classes/structs. The API currently defines a few interfaces with the consumer implements (eg: IAgent), using instances of their implementations (eg: MyAgent) to construct other API classes (eg: new Client(myAgent)). The API fires events. The API exposes a few delegate types. The API includes several enums. I'd like to release a version of the API as soon as possible and don't want to make major changes to it later if I realise it's too difficult to work with from F#. Any advice is appreciated.

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• How to store some of the entity's values in another table using hibernate?

  - by nimcap

  Hi guys, is there a simple way to persist some of the fields in another class and table using hibernate. For example, I have a Person class with name, surname, email, address1, address2, city, country fields. I want my classes to be: public class Person { private String name; private String surname; private String email; private Address address; // .. } public class Address { private Person person; // to whom this belongs private String address1; private String address2; private String city; private Address country; // .. } and I want to store Address in another table. What is the best way to achieve this? Edit: I am using annotations. It does not have to be the way I described, I am looking for best practices. PS. If there is a way to make Address immutable (to use as a value object) that is even better, or maybe not because I thought everything from wrong perspective :)

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• Are there more secure alternatives to the .Net SQLConnection class?

  - by KeyboardMonkey

  Hi SO people, I'm very surprised this issue hasn't been discussed in-depth: This article tells us how to use windbg to dump a running .Net process strings in memory. I spent much time researching the SecureString class, which uses unmanaged pinned memory blocks, and keeps the data encrypted too. Great stuff. The problem comes in when you use it's value, and assign it to the SQLConnection.ConnectionString property, which is of the System.String type. What does this mean? Well... It's stored in plain text Garbage Collection moves it around, leaving copies in memory It can be read with windbg memory dumps That totally negates the SecureString functionality! On top of that, the SQLConnection class is non-inheritable, I can't even roll my own with a SecureString property instead; Yay for closed-source. Yay. A new DAL layer is in progress, but for a new major version and for so many users it will be at least 2 years before every user is upgraded, others might stay on the old version indefinitely, for whatever reason. Because of the frequency the connection is used, marshalling from a SecureString won't help, since the immutable old copies stick in memory until GC comes around. Integrated Windows security isn't an option, since some clients don't work on domains, and other roam and connect over the net. How can I secure the connection string, in memory, so it can't be viewed with windbg?

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• Passing information safely between Wicket and Hibernate in long running conversations

  - by Peter Tillemans

  We are using Wicket with Hibernate in the background. As part of out UI we have quite long running conversations spanning multiple requests before the updated information is written back to the database. To avoid getting hibernate errors with detached objects we are now using value objects to transfer info from the service layer to Wicket. However we now end up with an explosion of almost the same objects : e.g. Answer (mapped entity saved in hibernate) AnswerVO (immutable value object) AnswerModel (A mutable bean in the session domain) IModel wrapped Wicket Model and usually this gets wrapped in a CompoundPropertyModel This plumbing becomes exponentially worse when collections to other objects are involved in the objects. There has to be a better way to organize this. Can anyone share tips to make this less onerous? Maybe make the value objects mutable so we can remove the need for a seaprate backing bean in Wicket? Use the entity beans but absolutely make dead-certain they are detached from hibernate. (easier said than done)? Some other tricks or patterns?

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• Why are symbols not frozen strings?

  - by Alex Chaffee

  I understand the theoretical difference between Strings and Symbols. I understand that Symbols are meant to represent a concept or a name or an identifier or a label or a key, and Strings are a bag of characters. I understand that Strings are mutable and transient, where Symbols are immutable and permanent. I even like how Symbols look different from Strings in my text editor. What bothers me is that practically speaking, Symbols are so similar to Strings that the fact that they're not implemented as Strings causes a lot of headaches. They don't even support duck-typing or implicit coercion, unlike the other famous "the same but different" couple, Float and Fixnum. The mere existence of HashWithIndifferentAccess, and its rampant use in Rails and other frameworks, demonstrates that there's a problem here, an itch that needs to be scratched. Can anyone tell me a practical reason why Symbols should not be frozen Strings? Other than "because that's how it's always been done" (historical) or "because symbols are not strings" (begging the question). Consider the following astonishing behavior: :apple == "apple" #=> false, should be true :apple.hash == "apple".hash #=> false, should be true {apples: 10}["apples"] #=> nil, should be 10 {"apples" => 10}[:apples] #=> nil, should be 10 :apple.object_id == "apple".object_id #=> false, but that's actually fine All it would take to make the next generation of Rubyists less confused is this: class Symbol < String def initialize *args super self.freeze end (and a lot of other library-level hacking, but still, not too complicated) See also: http://onestepback.org/index.cgi/Tech/Ruby/SymbolsAreNotImmutableStrings.red http://www.randomhacks.net/articles/2007/01/20/13-ways-of-looking-at-a-ruby-symbol Why does my code break when using a hash symbol, instead of a hash string? Why use symbols as hash keys in Ruby? What are symbols and how do we use them? Ruby Symbols vs Strings in Hashes Can't get the hang of symbols in Ruby

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• Using an embedded Word document to create a new instance of that document.

  - by jim

  For a variety of reasons that are immutable ... I have a Word document which contains a VBA application (the 'app document') which creates a new document based on another document (the 'template') which contains the framework for the new document. I want to embed the 'template' into the 'app document' so that I deliver one file and I know I am using the correct version of the 'template'. I have, so far, embedded the 'template' file into the 'app document' and can find it by looping through "ThisDocument.InlineShapes", looking at .Field.OleFormat.IconLabel to find the 'template' by its name. The inlineShape.Field.OleFormat.Object is the 'template' document itself, and I can .Activate it, which causes it to appear as a regular document. I try to do SaveAs, and it does in fact save the file as the name I give it, however, that saved-as file is not left open, just the embedded file. I can not .Activate the file and just save it, then open the saved file, but that seems more work than necessary. So ... is the way I am doing this "the way", or I have missed some obvious practice? TIA

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• Help thinking "Pythony"

  - by Josh

  I'm brand new to Python and trying to learn it by replicating the following C++ function into python // determines which words in a vector consist of the same letters // outputs the words with the same letters on the same line void equivalentWords(vector <string> words, ofstream & outFile) { outFile << "Equivalent words\n"; // checkedWord is parallel to the words vector. It is // used to make sure each word is only displayed once. vector <bool> checkedWord (words.size(), false); for(int i = 0; i < words.size(); i++) { if (!checkedWord[i]){ outFile << " "; for(int j = i; j < words.size(); j++){ if(equivalentWords(words[i], words[j], outFile)) { outFile << words[j] << " "; checkedWord[j] = true; } } outFile << "\n"; } } } In my python code (below), rather than having a second vector, I have a list ("words") of lists of a string, a sorted list of the chars in the former string (because strings are immutable), and a bool (that tells if the word has been checked yet). However, I can't figure out how to change a value as you iterate through a list. for word, s_word, checked in words: if not checked: for word1, s_word1, checked1 in words: if s_word1 == s_word: checked1 = True # this doesn't work print word1, print "" Any help on doing this or thinking more "Pythony" is appreciated.

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• Is there a term for this concept, and does it exist in a static-typed language?

  - by Strilanc

  Recently I started noticing a repetition in some of my code. Of course, once you notice a repetition, it becomes grating. Which is why I'm asking this question. The idea is this: sometimes you write different versions of the same class: a raw version, a locked version, a read-only facade version, etc. These are common things to do to a class, but the translations are highly mechanical. Surround all the methods with lock acquires/releases, etc. In a dynamic language, you could write a function which did this to an instance of a class (eg. iterate over all the functions, replacing them with a version which acquires/releases a lock.). I think a good term for what I mean is 'reflected class'. You create a transformation which takes a class, and returns a modified-in-a-desired-way class. Synchronization is the easiest case, but there are others: make a class immutable [wrap methods so they clone, mutate the clone, and include it in the result], make a class readonly [assuming you can identify mutating methods], make a class appear to work with type A instead of type B, etc. The important part is that, in theory, these transformations make sense at compile-time. Even though an ActorModel<T> has methods which change depending on T, they depend on T in a specific way knowable at compile-time (ActorModel<T> methods would return a future of the original result type). I'm just wondering if this has been implemented in a language, and what it's called.

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