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  • Don't understand the typing of Scala's delimited continuations (A @cps[B,C])

    - by jkff
    I'm struggling to understand what precisely does it mean when a value has type A @cps[B,C] and what types of this form should I assign to my values when using the delimited continuations facility. I've looked at some sources: http://lamp.epfl.ch/~rompf/continuations-icfp09.pdf http://www.scala-lang.org/node/2096 http://dcsobral.blogspot.com/2009/07/delimited-continuations-explained-in.html http://blog.richdougherty.com/2009/02/delimited-continuations-in-scala_24.html but they didn't give me much intuition into this. In the last link, the author tries to give an explicit explanation, but it is not clear enough anyway. The A here represents the output of the computation, which is also the input to its continuation. The B represents the return type of that continuation, and the C represents its "final" return type—because shift can do further processing to the returned value and change its type. I don't understand the difference between "output of the computation", "return type of the continuation" and "final return type of the continuation". They sound like synonyms.

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  • Rails polymorphic associations, two assoc types in one class

    - by snitko
    Consider a class: class Link < ActiveRecord::Base has_many :link_votes, :as => :vote_subject, :class_name => 'Vote' has_many :spam_votes, :as => :vote_subject, :class_name => 'Vote' end The problem is, when I'm adding a new vote with @link.link_votes << Vote.new the vote_subject_type is 'Link', while I wish it could be 'link_votes' or something like that. Is this an AR limitation or is there a way to workaround this thing? I've actually found one related answer, but I'm not quite sure about what it says: http://stackoverflow.com/questions/1168047/polymorphic-association-with-multiple-associations-on-the-same-model/1764117#1764117

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  • MS SQL Return 1 Row Per Boat

    - by Tyler
    Basically, what I want to do is join 4 tables together and return 1 row for each boat. Table Layouts [Boats] id, date, section, raft [Photos] id, boatid, pthurl, purl [River_Company] id, sort, company, company_short [River_Section] id, section Its very simple as far as structure, however, I've having the time of my life trying to get it to return only 1 row. No boat will ever be on the same day, the only thing that's messing this up is the photo table. If you know a better way for it to return the record table for all the boats boats and only 1 photo from the photo table, please, please post it!!

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  • hibernate column uniqueness question

    - by Seth
    I'm still in the process of learning hibernate/hql and I have a question that's half best practices question/half sanity check. Let's say I have a class A: @Entity public class A { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; @Column(unique=true) private String name = ""; //getters, setters, etc. omitted for brevity } I want to enforce that every instance of A that gets saved has a unique name (hence the @Column annotation), but I also want to be able to handle the case where there's already an A instance saved that has that name. I see two ways of doing this: 1) I can catch the org.hibernate.exception.ConstraintViolationException that could be thrown during the session.saveOrUpdate() call and try to handle it. 2) I can query for existing instances of A that already have that name in the DAO before calling session.saveOrUpdate(). Right now I'm leaning towards approach 2, because in approach 1 I don't know how to programmatically figure out which constraint was violated (there are a couple of other unique members in A). Right now my DAO.save() code looks roughly like this: public void save(A a) throws DataAccessException, NonUniqueNameException { Session session = sessionFactory.getCurrentSession(); try { session.beginTransaction(); Query query = null; //if id isn't null, make sure we don't count this object as a duplicate if(obj.getId() == null) { query = session.createQuery("select count(a) from A a where a.name = :name").setParameter("name", obj.getName()); } else { query = session.createQuery("select count(a) from A a where a.name = :name " + "and a.id != :id").setParameter("name", obj.getName()).setParameter("name", obj.getName()); } Long numNameDuplicates = (Long)query.uniqueResult(); if(numNameDuplicates > 0) throw new NonUniqueNameException(); session.saveOrUpdate(a); session.getTransaction().commit(); } catch(RuntimeException e) { session.getTransaction().rollback(); throw new DataAccessException(e); //my own class } } Am I going about this in the right way? Can hibernate tell me programmatically (i.e. not as an error string) which value is violating the uniqueness constraint? By separating the query from the commit, am I inviting thread-safety errors, or am I safe? How is this usually done? Thanks!

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  • Multiple file types in vim

    - by Chad
    When I am working on a PHP file for example the default filetype is php. This makes sense, however when that PHP file has HTML as well the filetype is still only php. For some plugins that means that I get the PHP functionality for that plugin, but miss out on the HTML functionality. A more specific situation where this happens is with my snippet plugin. I get php snippets and not html snippets when I am editing a php file. Possible solutions to this (which I obviously don't like, hence my posting this question) are: add a map to toggle between different filetypes when I am editing different sections of the file. update my php snippets file to include the html snippets as well (while this would work for the example above, it doesn't solve the fundamental problem). So, Is there a way to edit a file using multiple filetypes at the same time in vim?

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  • Should primitive types or non-primitive types be preferred in Java interfaces?

    - by Greg Mattes
    (I thought I once read something about this in a book, but now I'm not sure where to find it. If this question reminds you of some material that you've read, please post a reference!) What are the pros and the cons of primitives in interfaces? In other words, is one of these preferable to the other and why? Perhaps one is preferable to the other in certain contexts? public interface Foo { int getBar(); } or public interface Foo { Integer getBar(); } Similarly: public interface Boz { void someOperation(int parameter); } or public interface Boz { void someOperation(Integer parameter); } Obviously there's the issue of having to deal with nulls in the non-primitive case, but are there deeper concerns?

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  • Add Checkbox column in flexigrid

    - by Ramji
    The issue about jquery flexigrid using php. unfortunately http://flexigrid.info site is down very often so managed to take some sample code from http://sanderkorvemaker.nl/test/flexigrid/ and worked based on that. The above sample code works now I need to create a grid with a column with checkboxes, So that I can click a couple of those checkboxes and click delete button it should get all the id in which the checkboxes are checked to and create a delete query and execute. Can anyone give me an example please Thanks in advance

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  • devexpress ASPxGridView column problem

    - by oshafran
    Hey all I have an ASPXGRIDVIEW which is binded to an SQL query. I added to the grid an additional COLUMNCUSTOMBUTTON. But what happens is, that for all the rows it put a link there. I am trying to find a way to add to this column a link (button) ONLY to specific rows! I am unable to understand how to do it thanks

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  • Rows in their own columns depending on their date and simbolized by 'x'

    - by Chandradyani
    Dear All, please help me since I'm newbie in SQL Server. I have a select query that currently produces the following results: DoctorName Team Visit date dr. As A 5 dr. Sc A 4 dr. Gh B 6 dr. Nd C 31 dr As A 7 Using the following query: SELECT d.DoctorName, t.TeamName, ca.VisitDate FROM cActivity AS ca INNER JOIN doctor AS d ON ca.DoctorId = d.Id INNER JOIN team AS t ON ca.TeamId = t.Id WHERE ca.VisitDate BETWEEN '1/1/2010' AND '1/31/2010' I want to produce the following: DoctorName Team 1 2 3 4 5 6 7 ... 31 Visited dr. As A x x ... 2 times dr. Sc A x ... 1 times dr. Gh B x ... 1 times dr. Nd C ... X 1 times

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  • Binary comparison operators on generic types

    - by Brian Triplett
    I have a generic class that takes a type T. Within this class I have a method were I need to compare a type T to another type T such as: public class MyClass<T> { public T MaxValue { // Implimentation for MaxValue } public T MyMethod(T argument) { if(argument > this.MaxValue) { // Then do something } } } The comparison operation inside of MyMethod fails with Compiler Error CS0019. Is it possible to add a constraint to T to make this work? I tried adding a where T: IComparable<T> to the class definition to no avail.

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  • Formatting address of different types

    - by mickyjtwin
    I have various classes which all contain address details, i.e. AddressLine1, AddressLine2, AddressLine3, Suburb, Town, etc. On the front end, I need to format the address in a particular way, i.e. AddressLine1<br /> AddressLine2<br /> Suburb State Postcode If AddressLine2 does not exist or empty, don't show it. Quite straight-forward. I am trying to determine the best way to show this info. At the moment, the Address property of each class calls a FormatAddress method which writes out the html string. This exists as a method of the class. My opinion is that any formatting should exist from the front-end control i.e. ascx etc. However, if these DetailClasses need to format the same address info, what would be the best option, also making it easier to maintain?

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  • TSQL 'Invalid column name' error on value of sproc parameter

    - by Daria
    here's my code: DECLARE @SQL varchar(600) SET @SQL = 'SELECT CategoryID, SubCategoryID, ReportedNumber FROM tblStatistics WHERE UnitCode = ' + @unitCode + ' AND FiscYear = ' + @currYEAR EXEC (@SQL) When i run this sproc with unitCode = 'COB' and currYEAR = '10', i get the following error: Invalid column name 'COB'. Does anyone know why? thx!

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  • How to merge two single column csv files with linux commands

    - by user1328191
    I was wondering how to merge two single column csv files into one file where the resulting file will contain two columns. file1.csv    first_name    chris    ben    jerry file2.csv    last_name    smith    white    perry result.csv    first_name,last_name    chris,smith    ben,white    jerry,perry Thanks

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  • NHibernate: Mapping collections of value types

    - by Anry
    I have a table Order, Transaction, Payment. Class Order has the properties: public virtual Guid Id { get; set; } public virtual DateTime Created { get; set; } ... I added properties: public virtual IList<Transaction> Transactions { get; set; } public virtual IList<Payment> Payments { get; set; } These properties contain a record of tables [Transaction] and [Payment]. How to keep these lists in the database?

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  • How to introduce custom primitive key types to WCF Data Services (Astoria)

    - by Artem Tikhomirov
    Hello. We use custom type to represent Identifiers in our project. It has TypeConvertor attached and it always helped with serialization. I've tried to use WCF Data Services to expose some data from our system, but faced a problem. Astoria framework do not recognize class as an entity even though I've decorated it with [DataServiceKey("Id")] attribute. If I change type of property to Guid - it totally works :(. How could teach WCF Data Services to understand this simple class?

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  • F# Multidimensional Array Types

    - by SHiNKiROU
    What's the difference between 'a[,,] and 'a[][][]? They both represent 3-d arrays. It makes me write array3d.[x].[y].[z] instead of array3d.[x, y, z]. Why I can't do the following? > let array2d : int[,] = Array2D.zeroCreate 10 10;; > let array1d = array2d.[0];; error FS0001: This expression was expected to have type 'a [] but here has type int [,]

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  • Python In-memory table

    - by nsharish
    What is the right way to forming in-memory table in python with direct lookups for rows and columns.I thought of using dict of dicts this way, class Table(dict): def __getitem__(self, key): if key not in self: self[key]={} return dict.__getitem__(self, key) table = Table() table['row1']['column1'] = 'value11' table['row1']['column2'] = 'value12' table['row2']['column1'] = 'value21' table['row2']['column2'] = 'value22' >>>table {'row1':{'column1':'value11','column2':'value12'},'row2':{'column1':'value21','column2':'value22'}} I had difficulty in looking up for values in columns. >>>'row1' in table True >>>'value11' in table['row1'].values() True Now how do I do lookup if 'column1' has 'value11' Is this method of forming tables wrong?Is there a better way to implement such tables with easier lookups?.Thanks

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