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  • Private constructor and public parameter constructor -C#

    - by Amutha
    I heard that private constructor prevent object creation from outside world. When i have a code public class Product { public string Name { get;set;} public double Price {get;set;} Product() { } public Product(string _name,double _price) { } } here still i can declare public constructor(parameter),won't it spoil the purpose of private constructor? When do we need both private and public constructor(parameter) in code? I need detailed explanation please.

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  • WCF Named Pipe IPC

    - by Peter M
    I have been trying to get up to speed on Named Pipes this week. The task I am trying to solve with them is that I have an existing windows service that is acting as a device driver that funnels data from an external device into a database. Now I have to modify this service and add an optional user front end (on the same machine, using a form of IPC) that can monitor the data as it passes between the device and the DB as well as send some commands back to the service. My initial ideas for the IPC were either named pipes or memory mapped files. So far I have been working through the named pipe idea using WCF Tutorial Basic Interprocess Communication . My idea is to set the Windows service up with an additional thread that implements the WCF NamedPipe Service and use that as a conduit to the internals of my driver. I have the sample code working, however I can not get my head around 2 issues that I am hoping that someone here can help me with: In the tutorial the ServiceHost is instantiated with a typeof(StringReverser) rather than by referencing a concrete class. Thus there seems to be no mechanism for the Server to interact with the service itself (between the host.Open() and host.Close() lines). Is it possible to create a link between and pass information between the server and the class that actually implements the service? If so, how? If I run a single instance of the server and then run multiple instance of the clients, it seems that each client gets a separate instance of the service class. I tried adding some state information to the class implementing the service and it was only retained within the instance of the named pipe. This is possibly related to the first question, but is there anyway to force the named pipes to use the same instance of the class that is implementing the service? Finally, any thoughts on MMF vs Named Pipes? Thanks for you help

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  • There is no web named - Sharepoint Event Hander

    - by Roosh Malai
    I activated following code with feature (web level scope). Now when i add an item to any document library it should create a folder "". No folder is created and no error is given either. can anyone see what's is going on? I got the following from the log file. I found similar code all over google so I am kinda puzzled why is not working in my environment. Thanks using System; using System.Collections.Generic; using System.Text; using Microsoft.SharePoint; namespace AddaFolder { class clAddaFolder : SPItemEventReceiver { public override void ItemAdded(SPItemEventProperties properties) { base.ItemAdded(properties); using (SPSite currentSite = new SPSite(SPContext.Current.Site.Url)) using (SPWeb currentWeb = currentSite.OpenWeb(SPContext.Current.Web.Url)) { try { //SPListTemplateCollection coll = currentWeb.ListTemplates; //Get the current document library link SPList newList = currentWeb.GetList(SPContext.Current.Web.Url); //.Site.Url); //newList = currentWeb.Lists.Add("My TEST Folder",SPFileSystemObjectType.Folder); //newList.Lists.Items.Add("My TEST Folder", SPFileSystemObjectType.Folder); //newList.Update(); SPListItem newListItem; //newListItem = newList.Folders.Add("", SPFileSystemObjectType.Folder, "My Test Folder"); newListItem = newList.Folders.Add(newList.ToString(), SPFileSystemObjectType.Folder, "My Test Folder"); newListItem.Update(); } catch (SPException spEx) { throw spEx; } } } } } 04/03/2010 17:52:44.25 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Shared Documents/Forms/AllItems.aspx". 04/03/2010 17:52:44.26 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/My TEST Doc Library/Forms/AllItems.aspx". 04/03/2010 17:52:44.27 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Calendar/calendar.aspx". 04/03/2010 17:52:44.29 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Tasks/AllItems.aspx". 04/03/2010 17:52:44.30 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Team Discussion/AllItems.aspx". 04/03/2010 17:52:44.31 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Shared Documents/Forms/AllItems.aspx". 04/03/2010 17:52:44.32 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/My TEST Doc Library/Forms/AllItems.aspx". 04/03/2010 17:52:44.34 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Calendar/calendar.aspx". 04/03/2010 17:52:44.35 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Tasks/AllItems.aspx". 04/03/2010 17:52:44.36 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Team Discussion/AllItems.aspx". 04/03/2010 17:52:51.33 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Shared Documents/Forms/AllItems.aspx". 04/03/2010 17:52:51.34 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/My TEST Doc Library/Forms/AllItems.aspx". 04/03/2010 17:52:51.35 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Calendar/calendar.aspx". 04/03/2010 17:52:51.37 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Tasks/AllItems.aspx". 04/03/2010 17:52:51.38 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Team Discussion/AllItems.aspx". 04/03/2010 17:52:51.39 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Shared Documents/Forms/AllItems.aspx". 04/03/2010 17:52:51.40 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/My TEST Doc Library/Forms/AllItems.aspx". 04/03/2010 17:52:51.41 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Calendar/calendar.aspx". 04/03/2010 17:52:51.43 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Tasks/AllItems.aspx". 04/03/2010 17:52:51.44 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Team Discussion/AllItems.aspx". 04/03/2010 17:53:02.69 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Shared Documents/Forms/AllItems.aspx". 04/03/2010 17:53:02.71 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/My TEST Doc Library/Forms/AllItems.aspx". 04/03/2010 17:53:02.72 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Calendar/calendar.aspx". 04/03/2010 17:53:02.73 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Tasks/AllItems.aspx". 04/03/2010 17:53:02.74 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Team Discussion/AllItems.aspx". 04/03/2010 17:53:02.75 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Shared Documents/Forms/AllItems.aspx". 04/03/2010 17:53:02.76 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/My TEST Doc Library/Forms/AllItems.aspx". 04/03/2010 17:53:02.77 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Calendar/calendar.aspx". 04/03/2010 17:53:02.78 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Tasks/AllItems.aspx". 04/03/2010 17:53:02.79 w3wp.exe (0x00C0) 0x0C88 Windows SharePoint Services General 8kh7 High There is no Web named "/sites/myDevSiteColl/myDevWeb/Lists/Team Discussion/AllItems.aspx".

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  • Django: Named URLs / Same Template, Different Named URL

    - by TheLizardKing
    I have a webapp that lists all of my artists, albums and songs when the appropriate link is clicked. I make extensive use of generic views (object_list/detail) and named urls but I am coming across an annoyance. I have three templates that pretty much output the exact same html that look just like this: {% extends "base.html" %} {% block content %} <div id="content"> <ul id="starts-with"> {% for starts_with in starts_with_list %} <li><a href="{% url song_list_x starts_with %}">{{ starts_with|upper }}</a></li> {% endfor %} </ul> <ul> {% for song in songs_list %} <li>{{ song.title }}</li> {% endfor %} </ul> </div> {% endblock content %} My artist and album template look pretty much the same and I'd like to combine the three template's into one. The fact that my variables start with song can easily be changed to the default obj. It's my <ul id="starts-with"> named url I don't know how to correct. Obviously I want it to link to a specific album/artist/song using the named urls in my urls.py but I don't know how to make it context aware. Any suggestions? urlpatterns = patterns('tlkmusic.apps.tlkmusic_base.views', # (r'^$', index), url(r'^artists/$', artist_list, name='artist_list'), url(r'^artists/(?P<starts_with>\w)/$', artist_list, name='artist_list_x'), url(r'^artist/(?P<artist_id>\d+)/$', artist_detail, name='artist_detail'), url(r'^albums/$', album_list, name='album_list'), url(r'^albums/(?P<starts_with>\w)/$', album_list, name='album_list_x'), url(r'^songs/$', song_list, name='song_list'), url(r'^songs/(?P<starts_with>\w)/$', song_list, name='song_list_x'), )

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  • Need script to redirect STDIN & STDOUT to named pipes

    - by user54903
    I have an app that launches an authentication helper (my script) and uses STDIN/STDOUT to communicate. I want to re-direct STDIN and STDOUT from this script to two named pipes for interaction with another program. E.g.: SCRIPT_STDIN pipe1 SCRIPT_STDOUT < pipe2 Here is the flow I'm trying to accomplish: [Application] - Launches helper script, writes to helpers STDIN, reads from helpers STDOUT (example: STDIN:username,password; STDOUT:LOGIN_OK) [Helper Script] - Reads STDIN (data from app), forwards to PIPE1; reads from PIPE2, writes that back to the app on STDOUT [Other Process] - Reads from PIPE1 input, processes and returns results to PIPE2 The cat command can almost do what I want. If there were an option to copy STDIN to STDERR I could make cat do this with a command (assuming the fictitious option -e echos to STDERR rather than STDOUT): cat -e PIPE2 2PIPE1 (read from PIPE2 and write it to STDOUT, copy input, normally going to STDERR to PIPE1)

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  • Opt-out of copy constructor

    - by sheepsimulator
    This might be a silly question, but... I've been writing a number of classes that utilize non-copyable members. These classes are never initialized via the copy constructor in my source. When I try to compile without supplying my own copy-constructor, g++ throws out many errors about how it can't build a default copy constructor, due to the non-copyable member objects. Is there a way to tell the compiler to just not give me a copy constructor?

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  • Empty constructor or no constructor

    - by Ram
    Hi, I think it is not mandatory to have a default constructor in a class (C#). So in that situation shall I have a empty constructor in the class or I can skip it? Is it a best practice to have a default empty constructor? Class test { test() { } ...... } or Class test { ...... }

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  • testing if constructor in constructor chain

    - by Delan Azabani
    I'm attempting to implement a GTK+ inspired widget toolkit for the web in JavaScript. One of the constructor chains goes gtk.widget => gtk.container => gtk.bin => gtk.window Every gtk.widget has a showAll method, which, if and only if the widget is a gtk.container or derivative (such as gtk.bin or gtk.window), will recursively show the children of that widget. Obviously, if it isn't a gtk.container or derivative, we shouldn't do anything because the widget in question can't contain anything. For reference, here is my inheritance function; it's probably not the best, but it's a start: function inherit(target, parent) { target.prototype = new parent; target.prototype.constructor = target; } I know that I can check for the direct constructor like this: if (this.constructor === gtk.container) ... However, this only tests for direct construction and not, say, if the object is a gtk.bin or gtk.window. How can I test whether gtk.container is somewhere up in the constructor chain?

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  • Get list of named queries in NHibernate

    - by Dan
    I have a dozen or so named queries in my NHibernate project and I want to execute them against a test database in unit tests to make sure the syntax still matches the changing domain/database model. Currently I have a unit test for each named query where I get and execute the query, for example: IQuery query = session.GetNamedQuery("GetPersonSummaries"); var personSummaryArray = query.List(); Assert.That(personSummaryArray, Is.Not.Null); This works fine, but I would like to have one unit test that loops thru all of the named queries and executes them. Is there a way to discover all of the available named queries? Thanks Dan

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  • Named arguments in Mathematica.

    - by dreeves
    What's the best/canonical way to define a function with optional named arguments? To make it concrete, let's create a function foo with named arguments a, b, and c, which default to 1, 2, and 3, respectively. For comparison, here's a version of foo with positional arguments: foo[a_:1, b_:2, c_:3] := bar[a,b,c] Here is sample input and output for the named-arguments version of foo: foo[] --> bar[1,2,3] foo[b->7] --> bar[1,7,3] foo[a->6, b->7, c->8] --> bar[6,7,8] It should of course also be easy to have positional arguments before the named arguments.

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  • Init var without copy constructor

    - by Ockonal
    Hello, I have some class(Window) without copy constructor (it's private). I can't understand how to init var of this class in my own class: class MyClass { Window obj; // Hasn't copy constructor public: void init() { obj = Window(/* constructor params */); // [error] obj(/* constructor params */); // [error] } } Error 1: initializing argument 1 of ‘Window::Window(WindowHandle, const sf::WindowSettings&)’ Error 2: ‘NonCopyable& NonCopyable::operator=(const NonCopyable&)’ is private But it works in this way: Window obj(/* constructor params */);

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  • Doubt about constructor in JAVA

    - by Harry Joy
    I have few doubts regarding constructor in java Can a constructor be private? If yes then in which condition? Constructor is a method or not? If constructor does not return anything then why we are getting a new Object every time we call it. Whats the default access modifier of a constructor if we did not specify. Thanks & Regards Edit---------- Answer for 1 & 3 are very clear. But still doubt about 2&4 as i'm getting different answers for them.

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  • Beware when using .NET's named pipes in a windows forms application

    - by FransBouma
    Yesterday a user of our .net ORM Profiler tool reported that he couldn't get the snapshot recording from code feature working in a windows forms application. Snapshot recording in code means you start recording profile data from within the profiled application, and after you're done you save the snapshot as a file which you can open in the profiler UI. When using a console application it worked, but when a windows forms application was used, the snapshot was always empty: nothing was recorded. Obviously, I wondered why that was, and debugged a little. Here's an example piece of code to record the snapshot. This piece of code works OK in a console application, but results in an empty snapshot in a windows forms application: var snapshot = new Snapshot(); snapshot.Record(); using(var ctx = new ORMProfilerTestDataContext()) { var customers = ctx.Customers.Where(c => c.Country == "USA").ToList(); } InterceptorCore.Flush(); snapshot.Stop(); string error=string.Empty; if(!snapshot.IsEmpty) { snapshot.SaveToFile(@"c:\temp\generatortest\test2\blaat.opsnapshot", out error); } if(!string.IsNullOrEmpty(error)) { Console.WriteLine("Save error: {0}", error); } (the Console.WriteLine doesn't do anything in a windows forms application, but you get the idea). ORM Profiler uses named pipes: the interceptor (referenced and initialized in your application, the application to profile) sends data over the named pipe to a listener, which when receiving a piece of data begins reading it, asynchronically, and when properly read, it will signal observers that new data has arrived so they can store it in a repository. In this case, the snapshot will be the observer and will store the data in its own repository. The reason the above code doesn't work in windows forms is because windows forms is a wrapper around Win32 and its WM_* message based system. Named pipes in .NET are wrappers around Windows named pipes which also work with WM_* messages. Even though we use BeginRead() on the named pipe (which spawns a thread to read the data from the named pipe), nothing is received by the named pipe in the windows forms application, because it doesn't handle the WM_* messages in its message queue till after the method is over, as the message pump of a windows forms application is handled by the only thread of the windows forms application, so it will handle WM_* messages when the application idles. The fix is easy though: add Application.DoEvents(); right before snapshot.Stop(). Application.DoEvents() forces the windows forms application to process all WM_* messages in its message queue at that moment: all messages for the named pipe are then handled, the .NET code of the named pipe wrapper will react on that and the whole process will complete as if nothing happened. It's not that simple to just say 'why didn't you use a worker thread to create the snapshot here?', because a thread doesn't get its own message pump: the messages would still be posted to the window's message pump. A hidden form would create its own message pump, so the additional thread should also create a window to get the WM_* messages of the named pipe posted to a different message pump than the one of the main window. This WM_* messages pain is not something you want to be confronted with when using .NET and its libraries. Unfortunately, the way they're implemented, a lot of APIs are leaky abstractions, they bleed the characteristics of the OS objects they hide away through to the .NET code. Be aware of that fact when using them :)

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  • Achieve Named Criteria with multiple tables in EJB Data control

    - by Deepak Siddappa
    In EJB create a named criteria using sparse xml and in named criteria wizard, only attributes related to the that particular entities will be displayed.  So here we can filter results only on particular entity bean. Take a scenario where we need to create Named Criteria based on multiple tables using EJB. In BC4J we can achieve this by creating view object based on multiple tables. So in this article, we will try to achieve named criteria based on multiple tables using EJB.Implementation StepsCreate Java EE Web Application with entity based on Departments and Employees, then create a session bean and data control for the session bean.Create a Java Bean, name as CustomBean and add below code to the file. Here in java bean from both Departments and Employees tables three fields are taken. public class CustomBean { private BigDecimal departmentId; private String departmentName; private BigDecimal locationId; private BigDecimal employeeId; private String firstName; private String lastName; public CustomBean() { super(); } public void setDepartmentId(BigDecimal departmentId) { this.departmentId = departmentId; } public BigDecimal getDepartmentId() { return departmentId; } public void setDepartmentName(String departmentName) { this.departmentName = departmentName; } public String getDepartmentName() { return departmentName; } public void setLocationId(BigDecimal locationId) { this.locationId = locationId; } public BigDecimal getLocationId() { return locationId; } public void setEmployeeId(BigDecimal employeeId) { this.employeeId = employeeId; } public BigDecimal getEmployeeId() { return employeeId; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getFirstName() { return firstName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getLastName() { return lastName; } } Open the sessionEJb file and add the below code to the session bean and expose the method in local/remote interface and generate a data control for that. Note:- Here in the below code "em" is a EntityManager. public List<CustomBean> getCustomBeanFindAll() { String queryString = "select d.department_id, d.department_name, d.location_id, e.employee_id, e.first_name, e.last_name from departments d, employees e\n" + "where e.department_id = d.department_id"; Query genericSearchQuery = em.createNativeQuery(queryString, "CustomQuery"); List resultList = genericSearchQuery.getResultList(); Iterator resultListIterator = resultList.iterator(); List<CustomBean> customList = new ArrayList(); while (resultListIterator.hasNext()) { Object col[] = (Object[])resultListIterator.next(); CustomBean custom = new CustomBean(); custom.setDepartmentId((BigDecimal)col[0]); custom.setDepartmentName((String)col[1]); custom.setLocationId((BigDecimal)col[2]); custom.setEmployeeId((BigDecimal)col[3]); custom.setFirstName((String)col[4]); custom.setLastName((String)col[5]); customList.add(custom); } return customList; } Open the DataControls.dcx file and create sparse xml for customBean. In sparse xml navigate to Named criteria tab -> Bind Variable section, create two binding variables deptId,fName. In sparse xml navigate to Named criteria tab ->Named criteria, create a named criteria and map the query attributes to the bind variables. In the ViewController create a file jspx page, from data control palette drop customBeanFindAll->Named Criteria->CustomBeanCriteria->Query as ADF Query Panel with Table. Run the jspx page and enter values in search form with departmentId as 50 and firstName as "M". Named criteria will filter the query of a data source and display the result like below.

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  • Named pipe is not flushing in Python

    - by BrainCore
    I have a named pipe created via the os.mkfifo() command. I have two different Python processes accessing this named pipe, process A is reading, and process B is writing. Process A uses the select function to determine when there is data available in the fifo/pipe. Despite the fact that process B flushes after each write call, process A's select function does not always return (it keeps blocking as if there is no new data). After looking into this issue extensively, I finally just programmed process B to add 5KB of garbage writes before and after my real call, and likewise process A is programmed to ignore those 5KB. Now everything works fine, and select is always returning appropriately. I came to this hack-ish solution by noticing that process A's select would return if process B were to be killed (after it was writing and flushing, it would sleep on a read pipe). Is there a problem with flush in Python for named pipes?

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  • Whats the significance of named scope in rails?

    - by piemesons
    Before going for details. Question 1:-- Whats the meaning of scope here (ie named scope)? whats the benefits of using named scope? Now:- from agile development with rails book:-- class Order < ActiveRecord::Base named_scope :last_n_days, lambda { |days| {:conditions => ['updated < ?' , days] } } named_scope :checks, :conditions => {:pay_type => :check} end Such a named scope would make finding the last weeks worth of orders a snap. orders = Orders.last_n_days(7) Scopes can also be combined orders = Orders.checks.last_n_days(7) why we are using named_scope here. We can do the same using methods. Whats special thing we got using named_scope.

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  • C++ Array Initialization in Function Call or Constructor Call

    - by david
    This question is related to the post here. Is it possible to initialize an array in a function call or constructor call? For example, class foo's constructor wants an array of size 3, so I want to call foo( { 0, 0, 0 } ). I've tried this, and it does not work. I'd like to be able to initialize objects of type foo in other objects' constructor initialization lists, or initialize foo's without first creating a separate array. Is this possible?

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  • Accessing constructor from abstract base class with reflection

    - by craesh
    Hi! I'm playing around with Java's Reflection. I have an abstract class Base with a constructor. abstract class Base { public Base( String foo ) { // do some magic } } I have some further classes extending Base. They don't contain much logic. I want to instantiate them with Base's constructor, without having to write some proxy contructors in those derived classes. And of course, I want to instantiate those derived classes with Reflection. Say: Class cls = SomeDerivedClass.class; Constructor constr; constr = cls.getConstructor( new Class[] { String.class } ); // will return null Class clsBase = Base.class; constr = clsBase.getConstructor( new Class[] { String.class } ); // ok Base obj = (Base) constr.newInstance( new Object[] { "foo" } ); // will throw InstantiationException because it belongs to an abstract class Any ideas, how I can instantiate a derived class with Base's constructor? Or must I declare those dumb proxy constructors?

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  • Java constructor with large arguments or Java bean getter/setter approach

    - by deelo55
    Hi, I can't decide which approach is better for creating objects with a large number of fields (10+) (all mandatory) the constructor approach of the getter/setter. Constructor at least you enforce that all the fields are set. Java Beans easier to see which variables are being set instead of a huge list. The builder pattern DOES NOT seem suitable here as all the fields are mandatory and the builder requires you put all mandatory parameters in the builder constructor. Thanks, D

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  • Can a single argument constructor with a default value be subject to implicit type conversion

    - by Richard
    I understand the use of the explicit keyword to avoid the implicit type conversions that can occur with a single argument constructor, or with a constructor that has multiple arguments of which only the first does not have a default value. However, I was wondering, does a single argument constructor with a default value behave the same as one without a default value when it comes to implicit conversions?

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  • Getting the instance when Constructor#newInstance throws?

    - by Shtééf
    I'm working on a simple plugin system, where third party plugins implement a Plugin interface. A directory of JARs is scanned, and the implementing classes are instantiated with Constructor#newInstance. The thing is, these plugins call back into register* methods of the plugin host. These registrations use the Plugin instance as a handle. My problem is how to clean up these registrations if the constructor decides to fail and throw halfway through. InvocationTargetException doesn't seem to have anything on it to get the instance. Is there a way to get at the instance of an exception throwing constructor? P.S.: It's typically strongly advised to users that the constructor not do anything, but in practice people are doing it any ways.

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  • Good style for handling constructor failure of critical object

    - by mtlphil
    I'm trying to decide between two ways of instantiating an object & handling any constructor exceptions for an object that is critical to my program, i.e. if construction fails the program can't continue. I have a class SimpleMIDIOut that wraps basic Win32 MIDI functions. It will open a MIDI device in the constructor and close it in the destructor. It will throw an exception inherited from std::exception in the constructor if the MIDI device cannot be opened. Which of the following ways of catching constructor exceptions for this object would be more in line with C++ best practices Method 1 - Stack allocated object, only in scope inside try block #include <iostream> #include "simplemidiout.h" int main() { try { SimpleMIDIOut myOut; //constructor will throw if MIDI device cannot be opened myOut.PlayNote(60,100); //..... //myOut goes out of scope outside this block //so basically the whole program has to be inside //this block. //On the plus side, it's on the stack so //destructor that handles object cleanup //is called automatically, more inline with RAII idiom? } catch(const std::exception& e) { std::cout << e.what() << std::endl; std::cin.ignore(); return 1; } std::cin.ignore(); return 0; } Method 2 - Pointer to object, heap allocated, nicer structured code? #include <iostream> #include "simplemidiout.h" int main() { SimpleMIDIOut *myOut; try { myOut = new SimpleMIDIOut(); } catch(const std::exception& e) { std::cout << e.what() << std::endl; delete myOut; return 1; } myOut->PlayNote(60,100); std::cin.ignore(); delete myOut; return 0; } I like the look of the code in Method 2 better, don't have to jam my whole program into a try block, but Method 1 creates the object on the stack so C++ manages the object's life time, which is more in tune with RAII philosophy isn't it? I'm still a novice at this so any feedback on the above is much appreciated. If there's an even better way to check for/handle constructor failure in a siatuation like this please let me know.

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  • Issue calling superclass method in subclass constructor

    - by stormin986
    I get a NullPointerException calling a Superclass Method in Subclass Inner Class Constructor... What's the Deal? In my application's main class (subclass of Application), I have a public inner class that simply contains 3 public string objects. In the parent class I declare an object of that inner class. public class MainApplication extends Application { public class Data { public String x; public String y; public String z; } private Data data; MainApplication() { data = new Data() data.x = SuperClassMethod(); } } After I instantiate the object in the constructor, I get a runtime error when I try to assign a value in the inner class with a superclass method. Any idea what's up here?? Can you not call superclass methods in the subclass constructor? ** Edit ** Original question was about inner class member assignment in outer class constructor. Turned out the issue was with calling a superclass method in the class's constructor. It was giving me a null pointer exception. Thus, the question has changed.

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  • C++ superclass constructor calling rules

    - by levik
    What are the C++ rules for calling the superclass constructor from a subclass one?? For example I know in Java, you must do it as the first line of the subclass constructor (and if you don't an implicit call to a no-arg super constructor is assumed - giving you a compile error if that's missing).

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