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• Best Functional Approach

  - by dbyrne

  I have some mutable scala code that I am trying to rewrite in a more functional style. It is a fairly intricate piece of code, so I am trying to refactor it in pieces. My first thought was this: def iterate(count:Int,d:MyComplexType) = { //Generate next value n //Process n causing some side effects return iterate(count - 1, n) } This didn't seem functional at all to me, since I still have side effects mixed throughout my code. My second thought was this: def generateStream(d:MyComplexType):Stream[MyComplexType] = { //Generate next value n return Stream.cons(n, generateStream(n)) } for (n <- generateStream(initialValue).take(2000000)) { //process n causing some side effects } This seemed like a better solution to me, because at least I've isolated my functional value-generation code from the mutable value-processing code. However, this is much less memory efficient because I am generating a large list that I don't really need to store. This leaves me with 3 choices: Write a tail-recursive function, bite the bullet and refactor the value-processing code Use a lazy list. This is not a memory sensitive app (although it is performance sensitive) Come up with a new approach. I guess what I really want is a lazily evaluated sequence where I can discard the values after I've processed them. Any suggestions?

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• F# - POCO Class

  - by ebb

  Hey there! I'm trying to write a POCO class in proper F#... But something is wrong.. The C# code that I want to "translate" to proper F# is: public class MyTest { [Key] public int ID { get; set; } public string Name { get; set; } } The closest I can come to the above code in F# is something like: type Mytest() = let mutable _id : int = 0; let mutable _name : string = null; [<KeyAttribute>] member x.ID with public get() : int = _id and public set(value) = _id <- value member x.Name with public get() : string = _name and public set value = _name <- value However when I try to access the properties of the F# version it just returns a compile error saying "Lookup on object of indeterminate type based on information prior to this program point. A type annotation may be needed prior to this program point to constrain the type of the object. This may allow the lookup to be resolved." The code thats trying to get the property is a part of my Repository (I'm using EF Code First). module Databasethings = let GetEntries = let ctx = new SevenContext() let mydbset = ctx.Set<MyTest>() let entries = mydbset.Select(fun item -> item.Name).ToList() // This line comes up with a compile error at "item.Name" (the compile error is written above) entries What the hell is going on? Thanks in advance!

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• one-to-many with criteria question

  - by brnzn

  enter code hereI want to apply restrictions on the list of items, so only items from a given dates will be retrieved. Here are my mappings: <class name="MyClass" table="MyTable" mutable="false" > <cache usage="read-only"/> <id name="myId" column="myId" type="integer"/> <property name="myProp" type="string" column="prop"/> <list name="items" inverse="true" cascade="none"> <key column="myId"/> <list-index column="itemVersion"/> <one-to-many class="Item"/> </list> </class> <class name="Item" table="Items" mutable="false" > <cache usage="read-only"/> <id name="myId" column="myId" type="integer"/> <property name="itemVersion" type="string" column="version"/> <property name="startDate" type="date" column="startDate"/> </class> I tried this code: Criteria crit = session.createCriteria(MyClass.class); crit.add( Restrictions.eq("myId", new Integer(1))); crit = crit.createCriteria("items").add( Restrictions.le("startDate", new Date()) ); which result the following quires: select ... from MyTable this_ inner join Items items1_ on this_.myId=items1_.myId where this_.myId=? and items1_.startDate<=? followed by select ... from Items items0_ where items0_.myId=? But what I need is something like: select ... from MyTable this_ where this_.myId=? followed by select ... from Items items0_ where items0_.myId=? and items0_.startDate<=? Any idea how I can apply a criteria on the list of items?

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• one-to-many with criteria question

  - by brnzn

  enter code hereI want to apply restrictions on the list of items, so only items from a given dates will be retrieved. Here are my mappings: <class name="MyClass" table="MyTable" mutable="false" > <cache usage="read-only"/> <id name="myId" column="myId" type="integer"/> <property name="myProp" type="string" column="prop"/> <list name="items" inverse="true" cascade="none"> <key column="myId"/> <list-index column="itemVersion"/> <one-to-many class="Item"/> </list> </class> <class name="Item" table="Items" mutable="false" > <cache usage="read-only"/> <id name="myId" column="myId" type="integer"/> <property name="itemVersion" type="string" column="version"/> <property name="startDate" type="date" column="startDate"/> </class> I tried this code: Criteria crit = session.createCriteria(MyClass.class); crit.add( Restrictions.eq("myId", new Integer(1))); crit = crit.createCriteria("items").add( Restrictions.le("startDate", new Date()) ); which result the following quires: select ... from MyTable this_ inner join Items items1_ on this_.myId=items1_.myId where this_.myId=? and items1_.startDate<=? followed by select ... from Items items0_ where items0_.myId=? But what I need is something like: select ... from MyTable this_ where this_.myId=? followed by select ... from Items items0_ where items0_.myId=? and items0_.startDate<=? Any idea how I can apply a criteria on the list of items?

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• Make All Types Constant by Default in C++

  - by Jon Purdy

  What is the simplest and least obtrusive way to indicate to the compiler, whether by means of compiler options, #defines, typedefs, or templates, that every time I say T, I really mean T const? I would prefer not to make use of an external preprocessor. Since I don't use the mutable keyword, that would be acceptable to repurpose to indicate mutable state. Potential (suboptimal) solutions so far: // I presume redefinition of keywords is implementation-defined or illegal. #define int int const #define ptr * const int i(0); int ptr j(&i); typedef int const Int; typedef int const* const Intp; Int i(0); Intp j(&i); template<class T> struct C { typedef T const type; typedef T const* const ptr; }; C<int>::type i(0); C<int>::ptr j(&i);

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• What are graphs in laymen's terms

  - by Justin984

  What are graphs, in computer science, and what are they used for? In laymen's terms preferably. I have read the definition on Wikipedia: In computer science, a graph is an abstract data type that is meant to implement the graph and hypergraph concepts from mathematics. A graph data structure consists of a finite (and possibly mutable) set of ordered pairs, called edges or arcs, of certain entities called nodes or vertices. As in mathematics, an edge (x,y) is said to point or go from x to y. The nodes may be part of the graph structure, or may be external entities represented by integer indices or references. but I'm looking for a less formal, easier to understand definition.

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• Immutable Method in Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in C and C++. In the latter languages there are mutable and immutable methods such as stated in the answer by Johannes Schaub - litb to the question How many and which are the uses of “const” in C++? Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• Compute if a function is pure

  - by Oni

  As per Wikipedia: In computer programming, a function may be described as pure if both these statements about the function hold: The function always evaluates the same result value given the same argument value(s). The function result value cannot depend on any hidden information or state that may change as program execution proceeds or between different executions of the program, nor can it depend on any external input from I/O devices. Evaluation of the result does not cause any semantically observable side effect or output, such as mutation of mutable objects or output to I/O devices. I am wondering if it is possible to write a function that compute if a function is pure or not. Example code in Javascript: function sum(a,b) { return a+b; } function say(x){ console.log(x); } isPure(sum) // True isPure(say) // False

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• Immutable Method Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in c and c++. In the latter languages their is mutable and immutable methods such as stated in one answer by Johannes Schaub - litb the question how-many-and-which-are-the-uses-of-const-in-ce Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• Yippy &ndash; the F# MVVM Pattern

  - by MarkPearl

  I did a recent post on implementing WPF with F#. Today I would like to expand on this posting to give a simple implementation of the MVVM pattern in F#. A good read about this topic can also be found on Dean Chalk’s blog although my example of the pattern is possibly simpler. With the MVVM pattern one typically has 3 segments, the view, viewmodel and model. With the beauty of WPF binding one is able to link the state based viewmodel to the view. In my implementation I have kept the same principles. I have a view (MainView.xaml), and and a ViewModel (MainViewModel.fs).     What I would really like to illustrate in this posting is the binding between the View and the ViewModel so I am going to jump to that… In Program.fs I have the following code… module Program open System open System.Windows open System.Windows.Controls open System.Windows.Markup open myViewModels // Create the View and bind it to the View Model let myView = Application.LoadComponent(new System.Uri("/FSharpWPF;component/MainView.xaml", System.UriKind.Relative)) :?> Window myView.DataContext <- new MainViewModel() :> obj // Application Entry point [<STAThread>] [<EntryPoint>] let main(_) = (new Application()).Run(myView) You can see that I have simply created the view (myView) and then created an instance of my viewmodel (MainViewModel) and then bound it to the data context with the code… myView.DataContext <- new MainViewModel() :> obj If I have a look at my viewmodel (MainViewModel) it looks like this… module myViewModels open System open System.Windows open System.Windows.Input open System.ComponentModel open ViewModelBase type MainViewModel() = // private variables let mutable _title = "Bound Data to Textbox" // public properties member x.Title with get() = _title and set(v) = _title <- v // public commands member x.MyCommand = new FuncCommand ( (fun d -> true), (fun e -> x.ShowMessage) ) // public methods member public x.ShowMessage = let msg = MessageBox.Show(x.Title) () I have exposed a few things, namely a property called Title that is mutable, a command and a method called ShowMessage that simply pops up a message box when called. If I then look at my view which I have created in xaml (MainView.xaml) it looks as follows… <Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="F# WPF MVVM" Height="350" Width="525"> <Grid> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> <RowDefinition Height="*"/> </Grid.RowDefinitions> <TextBox Text="{Binding Path=Title, Mode=TwoWay}" Grid.Row="0"/> <Button Command="{Binding MyCommand}" Grid.Row="1"> <TextBlock Text="Click Me"/> </Button> </Grid> </Window>   It is also very simple. It has a button that’s command is bound to the MyCommand and a textbox that has its text bound to the Title property. One other module that I have created is my ViewModelBase. Right now it is used to store my commanding function but I would look to expand on it at a later stage to implement other commonly used functions… module ViewModelBase open System open System.Windows open System.Windows.Input open System.ComponentModel type FuncCommand (canExec:(obj -> bool),doExec:(obj -> unit)) = let cecEvent = new DelegateEvent<EventHandler>() interface ICommand with [<CLIEvent>] member x.CanExecuteChanged = cecEvent.Publish member x.CanExecute arg = canExec(arg) member x.Execute arg = doExec(arg) Put this all together and you have a basic project that implements the MVVM pattern in F#. For me this is quite exciting as it turned out to be a lot simpler to do than I originally thought possible. Also because I have my view in XAML I can use the XAML designer to design forms in F# which I believe is a much cleaner way to go rather than implementing it all in code. Finally if I look at my viewmodel code, it is actually quite clean and compact…

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• Result class dependency

  - by Stefano Borini

  I have an object containing the results of a computation. This computation is performed in a function which accepts an input object and returns the result object. The result object has a print method. This print method must print out the results, but in order to perform this operation I need the original input object. I cannot pass the input object at printing because it would violate the signature of the print function. One solution I am using right now is to have the result object hold a pointer to the original input object, but I don't like this dependency between the two, because the input object is mutable. How would you design for such case ?

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• Examples of "Lost art" on software technology/development

  - by mamcx

  With the advent of a new technology, some old ideas - despite been good - are forgotten in the process. I read a lot how some "new" thing was already present in Lisp like 60 years ago, but only recently resurface with other name or on top of another language. Now look like the new old thing is build functional, non-mutable, non-locking-thread stuff... and that make me wonder what have been "lost" in the art of development of software? What ideas are almost forgotten, waiting for resurface? One of my, I remember when I code in foxpro. The idea of have a full stack to develop database apps without impedance mismatch is something I truly miss. In the current languages, I never find another environment that match how easy was develop in fox back them. What else is missing?

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• in memory datastore in haskell

  - by Simon

  I want to implement an in memory datastore for a web service in Haskell. I want to run transactions in the stm monad. When I google hash table steam Haskell I only get this: Data. BTree. HashTable. STM. The module name and complexities suggest that this is implemented as a tree. I would think that an array would be more efficient for mutable hash tables. Is there a reason to avoid using an array for an STM hashtable? Do I gain anything with this stem hash table or should I just use a steam ref to an IntMap?

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• Should a primary key be immutable?

  - by Vincent Malgrat

  A recent question on stackoverflow provoked a discussion about the immutability of primary keys. I had thought that it was a kind of rule that primary keys should be immutable. If there is a chance that some day a primary key would be updated, I thought you should use a surrogate key. However it is not in the SQL standard and some RDBMS' "cascade update" feature allows a primary key to change. So my question is: is it still a bad practice to have a primary key that may change ? What are the cons, if any, of having a mutable primary key ?

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• What is the annoying/lacking feature in C#, in your opinion?

  - by Vimvq1987

  To be honest, I'm working with C# everyday, and I can say that I love its elegant syntax. But no language is perfect, so does C#. In my opinion, these two features are missing: Full-featured enum. I was pretty happy with enum in C#, until I know about enum in Java. Of course, we can "simulate" a full-featured enum in C# by class, but it's much better if Microsoft simplify this. Immutable keyword. We are told to let a class/struct immutable whenever possible. But to do that, we have to add readonly keyword to every field, and then if we add setter by a mistake, our class will be mutable, and nobody knows. By immutable keyword, every field will be automatically readonly, and any setter will be prohibited (error when compile). It's like static keyword added to class in C# 2.0 well. what's is your annoying/lacking feature in C#?

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• Immutable design with an ORM: How are sessions managed?

  - by Programmin Tool

  If I were to make a site with a mutable language like C# and use NHibernate, I would normally approach sessions with the idea of making them as create only when needed and dispose at request end. This has helped with keeping a session for multiple transactions by a user but keep it from staying open too long where the state might be corrupted. In an immutable system, like F#, I would think I shouldn't do this because it supposes that a single session could be updated constantly by any number of inserts/updates/deletes/ect... I'm not against the "using" solution since I would think that connecting pooling will help cut down on the cost of connecting every time, but I don't know if all database systems do connection pooling. It just seems like there should be a better way that doesn't compromise the immutability goal. Should I just do a simple "using" block per transaction or is there a better pattern for this?

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• Stateless game design

  - by L. De Leo

  I'm facing a challenge understanding how to program a web version of a card game that is completely stateless. I create my object graph when the game begins and distribute cards to PlayerA and PlayerB so I lay them out on the screen. At this point I could assume that HTML and the querystring is what holds at least some of my state and just keep a snapshot copy of the game state on the server-side for the sole purpose of validating the inputs I receive from the web clients. Still it appears to me that the state of the game is by its nature mutable: cards are being dealt from the deck, etc... Am I just not getting it? Or should I just strive to minimize the side-effects of my functions to the objects that I take as my input? How would you design a stateless card game?

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• Pooling (Singleton) Objects Against Connection Pools

  - by kolossus

  Given the following scenario A canned enterprise application that maintains its own connection pool A homegrown client application to the enterprise app. This app is built using Spring framework, with the DAO pattern While I may have a simplistic view of this, I think the following line of thinking is sound: Having a fixed pool of DAO objects, holding on to connection objects from the pool. Clearly, the pool should be capable of scaling up (or down depending on need) and the connection objects must outnumber the DAOs by a healthy margin. Good Instantiating brand new DAOs for every request to access the enterprise app; each DAO will attempt to grab a connection from the pool and release it when it's done. Bad Since these are service objects, there will be no (mutable) state held by the objects (reduced risk of concurrency issues) I also think that with #1, there should be little to no resource contention, while in #2, there'll almost always be a DAO waiting to be serviced. Is my thinking correct and what could go wrong?

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• Your favorite LiveCD

  - by sova

  Perhaps this is a question better suited for linux.se but since I have servers on all environments I was wondering what your favorite LiveCD is. Wiki defines this, for those unfamiliar, as a CD or DVD containing a bootable computer operating system. Live CDs are unique in that they have the ability to run a complete, modern operating system on a computer lacking mutable secondary storage, such as a hard disk drive. Live USB flash drives are similar to live CDs, but often have the added functionality of automatically and transparently writing changes back to their bootable medium. I tend to stick with Knoppix, and today I have to register the machine on the network before I can get any of my utilities running via IP. Any suggestions?

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• Naming convention: field starting with "m" or "s"

  - by Noya

  Hope this question hasn't posted yet... I saw lot of code (for example some Android source code) where fields name start with a "m" while static fields start with "s" Example (taken from Android View class source): private SparseArray<Object> mKeyedTags; private static int sNextAccessibilityViewId; I was wondering what "m" and "s" stand for... maybe is "m" mutable and "s" static? Since it seems that is a largely adopted pattern do you know if there some literature about this kind of naming convention?

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• NHibernate mapping with optimistic-lock="version" and dynamic-update="true" is generating invalid up

  - by SteveBering

  I have an entity "Group" with an assigned ID which is added to an aggregate in order to persist it. This causes an issue because NHibernate can't tell if it is new or existing. To remedy this issue, I changed the mapping to make the Group entity use optimistic locking on a sql timestamp version column. This caused a new issue. Group has a bag of sub objects. So when NHibernate flushes a new group to the database, it first creates the Group record in the Groups table, then inserts each of the sub objects, then does an update of the Group records to update the timestamp value. However, the sql that is generated to complete the update is invalid when the mapping is both dynamic-update="true" and optimistic-lock="version". Here is the mapping: <class xmlns="urn:nhibernate-mapping-2.2" dynamic-update="true" mutable="true" optimistic-lock="version" name="Group" table="Groups"> <id name="GroupNumber" type="System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="GroupNumber" length="5" /> <generator class="assigned" /> </id> <version generated="always" name="Timestamp" type="BinaryBlob" unsaved-value="null"> <column name="TS" not-null="false" sql-type="timestamp" /> </version> <property name="UID" update="false" type="System.Guid, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="GroupUID" unique="true" /> </property> <property name="Description" type="AnsiString"> <column name="GroupDescription" length="25" not-null="true" /> </property> <bag access="field.camelcase-underscore" cascade="all" inverse="true" lazy="true" name="Assignments" mutable="true" order-by="GroupAssignAssignment"> <key foreign-key="fk_Group_Assignments"> <column name="GroupNumber" /> </key> <one-to-many class="Assignment" /> </bag> <many-to-one class="Aggregate" name="Aggregate"> <column name="GroupParentID" not-null="true" /> </many-to-one> </class> </hibernate-mapping> When the mapping includes both the dynamic update and the optimistic lock, the sql generated is: UPDATE groups SET WHERE GroupNumber = 11111 AND TS=0x00000007877 This is obviously invalid as there are no SET statements. If I remove the dynamic update part, everything gets updated during this update statement instead. This makes the statement valid, but rather unnecessary. Has anyone seen this issue before? Am I missing something? Thanks, Steve

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• How to implement Persistent List or Persistent Mapping in ZODB

  - by gizgok

  One to many relationships not working in ZODB as list is mutable.They say solution is Persistent Mapping or Persistent List or BTree.Can someone please tell me how is it exactly done

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• Problem in running boost eample blocking_udp_echo_client on MacOSX

  - by n179911

  I am trying to run blocking_udp_echo_client on MacOS X http://www.boost.org/doc/libs/1_35_0/doc/html/boost_asio/example/echo/blocking_udp_echo_client.cpp I run it with argument 'localhost 9000' But the program crashes and this is the line in the source which crashes: `udp::socket s(io_service, udp::endpoint(udp::v4(), 0));' this is the stack trace: #0 0x918c3e42 in __kill #1 0x918c3e34 in kill$UNIX2003 #2 0x9193623a in raise #3 0x91942679 in abort #4 0x940d96f9 in __gnu_debug::_Error_formatter::_M_error #5 0x0000e76e in __gnu_debug::_Safe_iterator::op_base* , __gnu_debug_def::list::op_base*, std::allocator::op_base* ::_Safe_iterator at safe_iterator.h:124 #6 0x00014729 in boost::asio::detail::hash_map::op_base*::bucket_type::bucket_type at hash_map.hpp:277 #7 0x00019e97 in std::_Construct::op_base*::bucket_type, boost::asio::detail::hash_map::op_base*::bucket_type at stl_construct.h:81 #8 0x0001a457 in std::__uninitialized_fill_n_aux::op_base*::bucket_type*, __gnu_norm::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type , unsigned long, boost::asio::detail::hash_map::op_base*::bucket_type at stl_uninitialized.h:194 #9 0x0001a4e1 in std::uninitialized_fill_n::op_base*::bucket_type*, __gnu_norm::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type , unsigned long, boost::asio::detail::hash_map::op_base*::bucket_type at stl_uninitialized.h:218 #10 0x0001a509 in std::__uninitialized_fill_n_a::op_base*::bucket_type*, __gnu_norm::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type , unsigned long, boost::asio::detail::hash_map::op_base*::bucket_type, boost::asio::detail::hash_map::op_base*::bucket_type at stl_uninitialized.h:310 #11 0x0001aa34 in __gnu_norm::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type ::_M_fill_insert at vector.tcc:365 #12 0x0001acda in __gnu_norm::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type ::insert at stl_vector.h:658 #13 0x0001ad81 in __gnu_norm::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type ::resize at stl_vector.h:427 #14 0x0001ae3a in __gnu_debug_def::vector::op_base*::bucket_type, std::allocator::op_base*::bucket_type ::resize at vector:169 #15 0x0001b7be in boost::asio::detail::hash_map::op_base*::rehash at hash_map.hpp:221 #16 0x0001bbeb in boost::asio::detail::hash_map::op_base*::hash_map at hash_map.hpp:67 #17 0x0001bc74 in boost::asio::detail::reactor_op_queue::reactor_op_queue at reactor_op_queue.hpp:42 #18 0x0001bd24 in boost::asio::detail::kqueue_reactor::kqueue_reactor at kqueue_reactor.hpp:86 #19 0x0001c000 in boost::asio::detail::service_registry::use_service at service_registry.hpp:109 #20 0x0001c14d in boost::asio::use_service at io_service.ipp:195 #21 0x0001c26d in boost::asio::detail::reactive_socket_service ::reactive_socket_service at reactive_socket_service.hpp:111 #22 0x0001c344 in boost::asio::detail::service_registry::use_service at service_registry.hpp:109 #23 0x0001c491 in boost::asio::use_service at io_service.ipp:195 #24 0x0001c4d5 in boost::asio::datagram_socket_service::datagram_socket_service at datagram_socket_service.hpp:95 #25 0x0001c59e in boost::asio::detail::service_registry::use_service at service_registry.hpp:109 #26 0x0001c6eb in boost::asio::use_service at io_service.ipp:195 #27 0x0001c711 in boost::asio::basic_io_object ::basic_io_object at basic_io_object.hpp:72 #28 0x0001c783 in boost::asio::basic_socket ::basic_socket at basic_socket.hpp:108 #29 0x0001c865 in boost::asio::basic_datagram_socket ::basic_datagram_socket at basic_datagram_socket.hpp:107 #30 0x000027bc in main at main.cpp:32 This is the gdb output: (gdb) continue /Developer/SDKs/MacOSX10.5.sdk/usr/include/c++/4.0.0/debug/safe_iterator.h:127: error: attempt to copy-construct an iterator from a singular iterator. Objects involved in the operation: iterator "this" @ 0x0x100420 { type = N11__gnu_debug14_Safe_iteratorIN10__gnu_norm14_List_iteratorISt4pairIiPN5boost4asio6detail16reactor_op_queueIiE7op_baseEEEEN15__gnu_debug_def4listISB_SaISB_EEEEE (mutable iterator); state = singular; } iterator "other" @ 0x0xbfffe8a4 { type = N11__gnu_debug14_Safe_iteratorIN10__gnu_norm14_List_iteratorISt4pairIiPN5boost4asio6detail16reactor_op_queueIiE7op_baseEEEEN15__gnu_debug_def4listISB_SaISB_EEEEE (mutable iterator); state = singular; } Program received signal: “SIGABRT”. (gdb) continue Program received signal: “?”. Does someone has any idea why this example does not work on mac osx? Thank you.

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• Can immutable be a memory hog?

  - by ciscoheat

  Let's say we have a memory-intensive class like an Image, with chainable methods like Resize() and ConvertTo(). If this class is immutable, won't it take a huge amount of memory when I start doing things like i.Resize(500, 800).Rotate(90).ConvertTo(Gif), compared to a mutable one which modifies itself? How to handle a situation like this in a functional language?

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• scala integer weirdness

  - by williamstw

  Suppose you inadvertently use Integer instead of Int, as in this code: import scala.collection.mutable.Map val contributors = Map[String,Integer]() val count = contributors.getOrElseUpdate("john",0) contributors.put("john",count+1) println(contributors) Compiler output: (fragment of test.scala):7: error: type mismatch; found : Int(1) required: String contributors.put("john",count+1) ^ Why "required: String"?

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