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• how to implement lazy inheritance in javascript

  - by user283405

  how to implement lazy inheritance in javascript?

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• Scala's lazy arguments: How do they work?

  - by python dude

  In the file Parsers.scala (Scala 2.9.1) from the parser combinators library I seem to have come across a lesser known Scala feature called "lazy arguments". Here's an example: def ~ [U](q: => Parser[U]): Parser[~[T, U]] = { lazy val p = q // lazy argument (for(a <- this; b <- p) yield new ~(a,b)).named("~") } Apparently, there's something going on here with the assignment of the call-by-name argument q to the lazy val p. So far I have not been able to work out what this does and why it's useful. Can anyone help?

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• The difference between lists and sequences

  - by Peanut

  I'm trying to understand the difference between sequences and lists. In F# there is a clear distinction between the two. However in C# I have seen programmers refer to IEnumerable collections as a sequence. Is what makes IEnumerable a sequence the fact that it returns an object to iterate through the collection? Perhaps the real distinction is purely found in functional languages?

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• 50 sequences in one line

  - by user343934

  I have alignment file and long record in it. Suppose while displaying to an end user i want to show Sequence ID and 50 sequences in each line and continue further till the end of file. Can anyone suggest me algorithm or example code in python. Thanks in advance

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• Is there any reason lazy initialization couldn't be built into Java?

  - by Renesis

  Since I'm working on a server with absolutely no non-persisted state for users, every User-related object we have is rolled out on every request. Consequently I often find myself doing lazy initialization of properties of objects that may go unused. protected EventDispatcher dispatcher = new EventDispatcher(); Becomes... protected EventDispatcher<EventMessage> dispatcher; public EventDispatcher<EventMessage> getEventDispatcher() { if (dispatcher == null) { dispatcher = new EventDispatcher<EventMessage>(); } return dispatcher; } Is there any reason this couldn't be built into Java? protected lazy EventDispatcher dispatcher = new EventDispatcher();

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• Lazy Initailization in .NET 4.0

  Lazy initialization or lazy instantiation means that an object is not created until it is first referenced. Lazy initialization is used to reduce wasteful computation, memory requirements. Following is an example where Lazy initialization is particularly useful.

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• Dealing with sequences in OpenCV?

  - by Farhad

  I have 2 sequences. One (lets call this cvSeq x), which contains a number of contours (derived from cvFindContours) and a second (lets call this cvSeq y) which I have used cvCreateSeq upon, but doesn't actually have anything in it. I am looping through all the contours in x, and if a contour meets specific criteria, I add it to y. I am able to do the looping, but I don't know how to add an contour in x to y if it meets the criteria. Does anyone know how to add a contour in a sequence to another sequence (that is empty)? Code examples will be appreciated. PS: cvStartFindContours is not an option.

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• ConcurrentDictionary<TKey,TValue> used with Lazy<T>

  - by Reed

  In a recent thread on the MSDN forum for the TPL, Stephen Toub suggested mixing ConcurrentDictionary<T,U> with Lazy<T>.  This provides a fantastic model for creating a thread safe dictionary of values where the construction of the value type is expensive.  This is an incredibly useful pattern for many operations, such as value caches. The ConcurrentDictionary<TKey, TValue> class was added in .NET 4, and provides a thread-safe, lock free collection of key value pairs.  While this is a fantastic replacement for Dictionary<TKey, TValue>, it has a potential flaw when used with values where construction of the value class is expensive. The typical way this is used is to call a method such as GetOrAdd to fetch or add a value to the dictionary.  It handles all of the thread safety for you, but as a result, if two threads call this simultaneously, two instances of TValue can easily be constructed. If TValue is very expensive to construct, or worse, has side effects if constructed too often, this is less than desirable.  While you can easily work around this with locking, Stephen Toub provided a very clever alternative – using Lazy<TValue> as the value in the dictionary instead. This looks like the following.  Instead of calling: MyValue value = dictionary.GetOrAdd( key, () => new MyValue(key)); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } We would instead use a ConcurrentDictionary<TKey, Lazy<TValue>>, and write: MyValue value = dictionary.GetOrAdd( key, () => new Lazy<MyValue>( () => new MyValue(key))) .Value; This simple change dramatically changes how the operation works.  Now, if two threads call this simultaneously, instead of constructing two MyValue instances, we construct two Lazy<MyValue> instances. However, the Lazy<T> class is very cheap to construct.  Unlike “MyValue”, we can safely afford to construct this twice and “throw away” one of the instances. We then call Lazy<T>.Value at the end to fetch our “MyValue” instance.  At this point, GetOrAdd will always return the same instance of Lazy<MyValue>.  Since Lazy<T> doesn’t construct the MyValue instance until requested, the actual MyClass instance returned is only constructed once.

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• jsf datatable lazy load filter and sorting

  - by darko petreski

  Hi, I have worked on several projects with a lot of data tables. The tables had sorting, filtering and paging of course on server side and with help of the db (all databases has implemented sording, filtering -where and limit the returned results). When workig on real application there are a thousands of even a millions rows. But I have seen several JSF dagatable components. They implement pagination, sorting and filtering on client side!! According to me this is very silly. This technology is called enterprise and they sort the data on the client side with java script! I have not seen any good JSF data grid that has build in features for sorting, filtering and lazy loading on the server side. Why is that? Am I looking in wrong direction or really there in no build support for this. Lately I am testing primefaces and lazy loading datatable. It really works fine, but the table i can only lazy load. If you add sort and filter then the problems begin. Conclusion: Is there any datatable JSF component than can perform lazy load pagination, and filtering and sorting on server side. If I need to implement my own solution thanks to the teams that made client side sorting and filtering, they are useless. Regards

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• Lazy loading of Blob properties of one class

  - by Khosro

  Hi, My class contains "summary" and "title" properties those are Blob and other properties. Code:(I write some part of class) public class News extends BaseEntity{ @Lob @Basic(fetch = FetchType.LAZY) public String getSummary() { return summary; } @Lob @Basic(fetch = FetchType.LAZY) public String getTitle() { return title; } @Temporal(TemporalType.TIMESTAMP) public Date getPublishDate() { return publishDate; } } I instrument this class to lazy load of Blob properties using this class "org.hibernate.tool.instrument.javassist.InstrumentTask". When i write this code to retrieve only summary of new , newsDAO.findByid(1L).getSummary(); Hibernate generates these queries: Hibernate: select news0_.id as id1_, news0_.entityVersion as entityVe2_1_, news0_.publishDate as publish15_1_, news0_.url as url1_ from News news0_ Hibernate: select news_.summary as summary1_, news_.title as title1_ from News news_ where news_.id=? I have two qurestions: 1.I only want to retrieve "summary" property not "title" property,but Hibernate queries show that it also retrieve "title" property,Why this happens(i want to lazy load of "property")? It seems when i load one of Blob property ,Hibernate loads all of them.Why?(This is my main question) 2.Why Hibernate generates two queries for retrieving only "summary" property of news? Khosro.

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• NHibernate lazy properties behavior?

  - by GeReV

  I've been trying to get NHibernate into development for a project I'm working on at my workplace. Since I have to put a strong emphasis on performance, I've been running a proof-of-concept stress test on an existing project's table with thousands of records, all of which contain a large text column. However, when selecting a collection of these records, the select statement takes a relatively long time to execute; apparently due to the aforementioned column. The first solution that comes to mind is setting this property as lazy: <property name="Content" lazy="true"/> But there seems to be no difference in the SQL generated by NHibernate. My question is, how do lazy properties behave in NHibernate? Is there some kind of type limitations I could be missing? Should I take a different approach altogether? Using HQL's new Class(column1, column2) approach works, but lazy properties sounds like a simpler solution. It's perhaps worth mentioning I'm using NHibernate 2.1.2GA with the Castle DynamicProxy. Thanks!

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• Thread-Safe lazy instantiating using MEF

  - by Xaqron

  // Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• How to solve lazy initialization exception using JPA and Hibernate as provider

  - by rupertin

  I am working on a project for a customer who wants to use lazy initialization. They always get "lazy initialization exception" when mapping classes with the default lazy loading mode. @JoinTable(name = "join_profilo_funzionalita", joinColumns = {@JoinColumn(name = "profilo_id", referencedColumnName = "profilo_id")}, inverseJoinColumns = {@JoinColumn(name = "funzionalita_id", referencedColumnName = "funzionalita_id")}) //@ManyToMany(fetch=FetchType.EAGER) - no exceptions if uncommented @ManyToMany private Collection<Funzionalita> funzionalitaIdCollection; Is there a standard pattern using JPA classes to avoid this error? Snippets are welcome, thanks a lot for your time.

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• Paging over a lazy-loaded collection with NHibernate

  - by HackedByChinese

  I read this article where Ayende states NHibernate can (compared to EF 4): Collection with lazy=”extra” – Lazy extra means that NHibernate adapts to the operations that you might run on top of your collections. That means that blog.Posts.Count will not force a load of the entire collection, but rather would create a “select count(*) from Posts where BlogId = 1” statement, and that blog.Posts.Contains() will likewise result in a single query rather than paying the price of loading the entire collection to memory. Collection filters and paged collections - this allows you to define additional filters (including paging!) on top of your entities collections, which means that you can easily page through the blog.Posts collection, and not have to load the entire thing into memory. So I decided to put together a test case. I created the cliché Blog model as a simple demonstration, with two classes as follows: public class Blog { public virtual int Id { get; private set; } public virtual string Name { get; set; } public virtual ICollection<Post> Posts { get; private set; } public virtual void AddPost(Post item) { if (Posts == null) Posts = new List<Post>(); if (!Posts.Contains(item)) Posts.Add(item); } } public class Post { public virtual int Id { get; private set; } public virtual string Title { get; set; } public virtual string Body { get; set; } public virtual Blog Blog { get; private set; } } My mappings files look like this: <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true"> <class xmlns="urn:nhibernate-mapping-2.2" name="Model.Blog, TestEntityFramework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="Blogs"> <id name="Id" type="System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Id" /> <generator class="identity" /> </id> <property name="Name" type="System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Name" /> </property> <property name="Type" type="System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Type" /> </property> <bag lazy="extra" name="Posts"> <key> <column name="Blog_Id" /> </key> <one-to-many class="Model.Post, TestEntityFramework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" /> </bag> </class> </hibernate-mapping> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true"> <class xmlns="urn:nhibernate-mapping-2.2" name="Model.Post, TestEntityFramework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="Posts"> <id name="Id" type="System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Id" /> <generator class="identity" /> </id> <property name="Title" type="System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Title" /> </property> <property name="Body" type="System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Body" /> </property> <many-to-one class="Model.Blog, TestEntityFramework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="Blog"> <column name="Blog_id" /> </many-to-one> </class> </hibernate-mapping> My test case looks something like this: using (ISession session = Configuration.Current.CreateSession()) // this class returns a custom ISession that represents either EF4 or NHibernate { blogs = (from b in session.Linq<Blog>() where b.Name.Contains("Test") orderby b.Id select b); Console.WriteLine("# of Blogs containing 'Test': {0}", blogs.Count()); Console.WriteLine("Viewing the first 5 matching Blogs."); foreach (Blog b in blogs.Skip(0).Take(5)) { Console.WriteLine("Blog #{0} \"{1}\" has {2} Posts.", b.Id, b.Name, b.Posts.Count); Console.WriteLine("Viewing first 5 matching Posts."); foreach (Post p in b.Posts.Skip(0).Take(5)) { Console.WriteLine("Post #{0} \"{1}\" \"{2}\"", p.Id, p.Title, p.Body); } } } Using lazy="extra", the call to b.Posts.Count does do a SELECT COUNT(Id)... which is great. However, b.Posts.Skip(0).Take(5) just grabs all Posts for Blog.Id = ?id, and then LINQ on the application side is just taking the first 5 from the resulting collection. What gives?

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• Lazy evaluation in Ruby

  - by fifigyuri

  I have a situation for Ruby, where an object is possibly necessary to be created, but it is not sure. And as the creation of the object might be costly I am not too eager creating it. I think this is a clear case for lazy loading. How can I define an object which is not created only when someone sends a message to it? The object would be created in a block. Is there a way for simple lazy loading/initialisation in Ruby? Are these things supported by some gems, which provide different solutions for various cases of lazy initialisation of objects? Thanks for your suggestions!

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• make a lazy var in scala

  - by ayvango

  Scala does not permit to create laze vars, only lazy vals. It make sense. But I've bumped on use case, where I'd like to have similar capability. I need a lazy variable holder. It may be assigned a value that should be calculated by time-consuming algorithm. But it may be later reassigned to another value and I'd like not to call first value calculation at all. Example assuming there is some magic var definition lazy var value : Int = _ val calc1 : () => Int = ... // some calculation val calc2 : () => Int = ... // other calculation value = calc1 value = calc2 val result : Int = value + 1 This piece of code should only call calc2(), not calc1 I have an idea how I can write this container with implicit conversions and and special container class. I'm curios if is there any embedded scala feature that doesn't require me write unnecessary code

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• Prevent lazy loading in nHibernate

  - by Ciaran

  Hi, I'm storing some blobs in my database, so I have a Document table and a DocumentContent table. Document contains a filename, description etc and has a DocumentContent property. I have a Silverlight client, so I don't want to load up and send the DocumentContent to the client unless I explicity ask for it, but I'm having trouble doing this. I've read the blog post by Davy Brion. I have tried placing lazy=false in my config and removing the virtual access modifier but have had no luck with it as yet. Every time I do a Session.Get(id), the DocumentContent is retrieved via an outer join. I only want this property to be populated when I explicity join onto this table and ask for it. Any help is appreciated. My NHibernate mapping is as follows: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Jrm.Model" namespace="Jrm.Model"> <class name="JrmDocument" lazy="false"> <id name="JrmDocumentID"> <generator class="native" /> </id> <property name="FileName"/> <property name="Description"/> <many-to-one name="DocumentContent" class="JrmDocumentContent" unique="true" column="JrmDocumentContentID" lazy="false"/> </class> <class name="JrmDocumentContent" lazy="false"> <id name="JrmDocumentContentID"> <generator class="native" /> </id> <property name="Content" type="BinaryBlob" lazy="false"> <column name="FileBytes" sql-type="varbinary(max)"/> </property> </class> </hibernate-mapping> and my classes are: [DataContract] public class JrmDocument : ModelBase { private int jrmDocumentID; private JrmDocumentContent documentContent; private long maxFileSize; private string fileName; private string description; public JrmDocument() { } public JrmDocument(string fileName, long maxFileSize) { DocumentContent = new JrmDocumentContent(File.ReadAllBytes(fileName)); FileName = new FileInfo(fileName).Name; } [DataMember] public virtual int JrmDocumentID { get { return jrmDocumentID; } set { jrmDocumentID = value; OnPropertyChanged("JrmDocumentID"); } } [DataMember] public JrmDocumentContent DocumentContent { get { return documentContent; } set { documentContent = value; OnPropertyChanged("DocumentContent"); } } [DataMember] public virtual long MaxFileSize { get { return maxFileSize; } set { maxFileSize = value; OnPropertyChanged("MaxFileSize"); } } [DataMember] public virtual string FileName { get { return fileName; } set { fileName = value; OnPropertyChanged("FileName"); } } [DataMember] public virtual string Description { get { return description; } set { description = value; OnPropertyChanged("Description"); } } } [DataContract] public class JrmDocumentContent : ModelBase { private int jrmDocumentContentID; private byte[] content; public JrmDocumentContent() { } public JrmDocumentContent(byte[] bytes) { Content = bytes; } [DataMember] public int JrmDocumentContentID { get { return jrmDocumentContentID; } set { jrmDocumentContentID = value; OnPropertyChanged("JrmDocumentContentID"); } } [DataMember] public byte[] Content { get { return content; } set { content = value; OnPropertyChanged("Content"); } } }

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• Searching integer sequences

  - by David Gibson

  I have a fairly complex search problem that I've managed to reduce to the following description. I've been googling but haven't been able to find an algorithm that seems to fit my problem cleanly. In particular the need to skip arbitrary integers. Maybe someone here can point me to something? Take a sequence of integers A, for example (1 2 3 4) Take various sequences of integers and test if any of them match A such that. A contains all of the integers in the tested sequence The ordering of the integers in the tested sequence are the same in A We don't care about any integers in A that are not in the test sequence We want all matching test sequences, not just the first. An example A = (1 2 3 4) B = (1 3) C = (1 3 4) D = (3 1) E = (1 2 5) B matches A C matches A D does not match A as the ordering is different E does not match A as it contains an integer not in A I hope that this explanation is clear enough. The best I've managed to do is to contruct a tree of the test sequences and iterate over A. The need to be able to skip integers leads to a lot of unsuccessful search paths. Thanks Reading some suggestions I feel that I have to clarify a couple of points that I left too vague. Repeated numbers are allowed, in fact this is quite important as it allows a single test sequence to match A is multiple ways A = (1234356), B = (236), matches could be either -23---6 or -2--3-6 I expect there to be a very large number of test sequences, in the thousands at least and sequence A will tend to have a max length of maybe 20. Thus simply trying to match each test sequence one by one by iterating becomes extremely inefficient. Sorry if this wasn't clear.

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• Lazy Loading in dynatree

  - by gnomixa

  In this component http://wwwendt.de/tech/dynatree/index.html under 5.4 Loading child nodes on demand ('lazy loading') it seems that the only way to load the tree nodes in a lazy manner is to grab them from web service. What if I want to grab the nodes from a data structure? Any advice?

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• Disable lazy loading by default in Entity Framework 4

  - by Mikey Cee

  It seems that lazy loading is enabled by default in EF4. At least, in my project, I can see that the value of dataContext.ContextOptions.LazyLoadingEnabled is true by default. I don't want lazy loading and I don't want to have to write: dataContext.ContextOptions.LazyLoadingEnabled = false; each time I get a new context. So is there a way to turn it off by default, say, across the whole project?

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• What is Lazy Loading?

  - by Brian Boatright

  What is Lazy Loading? [Edit after reading a few answers] Why do people use this term so often? Say you just use a ASP/ADO recordset and load it with data or ADO.NET Datasource for a gridview. I guess I should have asked why people use the term Lazy Loading, what "other" types are their?

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• What is lazy loading in Hibernate?

  - by rocker

  What is lazy loading in Java? I don't understand the process. Can anybody help me to understand the process of lazy loading?

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• Oracle Sequences

  - by jkrebsbach

  Reminder to myself - SQL Server has nice index columns directly tied to their tables. Oracle has sequences that are islands to themselves. select seq_name.currval from dual; select seq_name.nextval from dual; currval - return current number at top of sequence nextval - increment sequence by 1, return new number   therefore - to create functionality in oracle similar to an index column - OPTION A) - Create insert trigger: CREATE OR REPLACE TRIGGER dept_bir BEFORE INSERT ON departments FOR EACH ROW WHEN (new.id IS NULL) BEGIN SELECT dept_seq.NEXTVAL INTO :new.id FROM dual; END; This will handle creating a unique identity, but will not necessarily inform process flow of identity without additional logic. OPTION B) - Select indentity into temp variable, insert whole item into tab **** When attemptint to query currval, the below error was being thrown - SELECT seq_name.currval from dual; ERROR : TABLE OR VIEW DOES NOT EXIST *** Although Oracle sys tables may have access to the sequences, that isn't to say the Oracle user may have access to those sequences - verify permissions when the system can't see object that are being reported in the object explorer.

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• Entity Framework 4.0: Creating objects of correct type when using lazy loading

  - by DigiMortal

  In my posting about Entity Framework 4.0 and POCOs I introduced lazy loading in EF applications. EF uses proxy classes for lazy loading and this means we have new types in that come and go dynamically in runtime. We don’t have these types available when we write code but we cannot forget that EF may expect us to use dynamically generated types. In this posting I will give you simple hint how to use correct types in your code. The background of lazy loading and proxy classes As a first thing I will explain you in short what is proxy class. Business classes when designed correctly have no knowledge about their birth and death – they don’t know how they are created and they don’t know how their data is persisted. This is the responsibility of object runtime. When we use lazy loading we need a little bit different classes that know how to load data for properties when code accesses the property first time. As we cannot add this functionality to our business classes (they may be stored through more than one data access technology or by more than one Data Access Layer (DAL)) we create proxy classes that extend our business classes. If we have class called Product and product has lazy loaded property called Customer then we need proxy class, let’s say ProductProxy, that has same public signature as Product so we can use it INSTEAD OF product in our code. ProductProxy overrides Customer property. If customer is not asked then customer is null. But if we ask for Customer property then overridden property of ProductProxy loads it from database. This is how lazy loading works. Problem – two types for same thing As lazy loading may introduce dynamically generated proxy types we don’t know in our application code which type is returned. We cannot be sure that we have Product not ProductProxy returned. This leads us to the following question: how can we create Product of correct type if we don’t know the correct type? In EF solution is simple. Solution – use factory methods If you are using repositories and you are not using factories (imho it is pretty pointless with mapper) you can add factory methods to your EF based repositories. Take a look at this class. public class Event {     public int ID { get; set; }     public string Title { get; set; }     public string Location { get; set; }     public virtual Party Organizer { get; set; }     public DateTime Date { get; set; } } We have virtual member called Organizer. This property is virtual because we want to use lazy loading on this class so Organizer is loaded only when we ask it. EF provides us with method called CreateObject<T>(). CreateObject<T>() is member of ObjectContext class and it creates the object based on given type. In runtime proxy type for Event is created for us automatically and when we call CreateObject<T>() for Event it returns as object of Event proxy type. The factory method for events repository is as follows. public Event CreateEvent() {     var evt = _context.CreateObject<Event>();     return evt; } And we are done. Instead of creating factory classes we created factory methods that guarantee that created objects are of correct type. Conclusion Although lazy loading introduces some new objects we cannot use at design time because they live only in runtime we can write code without worrying about exact implementation type of object. This holds true until we have clean code and we don’t make any decisions based on object type. EF4.0 provides us with very simple factory method that create and return objects of correct type. All we had to do was adding factory methods to our repositories.

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• Iterator blocks in Clojure?

  - by Checkers

  I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (with-connection *db* (with-query-results res ["select * from foo"] (into [] res)))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL-related bindings will be reset and connection will be closed after I return, so realizing the sequence will throw an exception. How can I enclose the whole function in a closure and return a kind of iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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