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• Constructor with non-instance variable assistant?

  - by Robert Fischer

  I have a number of classes that look like this: class Foo(val:BasicData) extends Bar(val) { val helper = new Helper(val) val derived1 = helper.getDerived1Value() val derived2 = helper.getDerived2Value() } ...except that I don't want to hold onto an instance of "helper" beyond the end of the constructor. In Java, I'd do something like this: public class Foo { final Derived derived1, derived2; public Foo(BasicData val) { Helper helper = new Helper(val); derived1 = helper.getDerived1Value(); derived2 = helper.getDerived2Value(); } } So how do I do something like that in Scala? I'm aware of creating a helper object of the same name of the class with an apply method: I was hoping for something slightly more succinct.

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• C++ catch constructor exception

  - by aaa

  hi. I do not seem to understand how to catch constructor exception. Here is relevant code: struct Thread { rysq::cuda::Fock fock_; template<class iterator> Thread(const rysq::cuda::Centers &centers, const iterator (&blocks)[4]) : fock_() { if (!fock_) throw; } }; Thread *ct; try { ct = new Thread(centers_, blocks); } catch(...) { return false; } // catch never happens, So catch statement do not execute and I get unhandled exception. What did I do wrong? this is straight C++ using g++.

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• Disallow private constructor invocation in friend function

  - by user2907032

  Is there any way to not allow private construction in friend function, In case we do have private constructor with friend function in our class. Only Static method should be responsible for object creation and other than this compiler should flash error message #include <iostream> #include <memory> using namespace std; class a { public: void see () { cout<<"Motimaa"; } static a& getinstance() { static a instance; return instance; } private: a() {}; friend void access(); }; void access () { a obj; obj.see();//still friend function can access } int main() { a::getinstance().see(); access(); return 1; }

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• How do I get the default constructor value in a function

  - by lax

  public class AppXmlLogWritter { public int randomNumber; public string LogDateTime = ""; public AppXmlLogWritter() { Random random = new Random(); randomNumber = random.Next(9999); LogDateTime = DateTime.Now.ToString("yyyyMMdd HHmmss"); } public AppXmlLogWritter(int intLogIDPrefix, string strLogApplication, string strLogFilePath) { LogIDPrefix = intLogIDPrefix; LogApplication = strLogApplication; LogFilePath = strLogFilePath; } public void WriteXmlLog(string LogFlag) { string value=LogDateTime + randomNumber;**//Here i m getting 0 no date time and random number generated** } } AppXmlLogWritter objParameterized = new AppXmlLogWritter(1234, "LogApplication", "LogFilepath"); AppXmlLogWritter objParmeterlessConstr = new AppXmlLogWritter(); objParameterized.WriteXmlLog("0", "LogFlag"); How do I get the default constructor value in this function?

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• C# Closing a form during a constructor

  - by pm_2

  Is it possible to close a form while the constructor is executing (or simply to stop it showing at this stage)? I have the following code: public partial class MyForm : Form { public MyForm() { if (MyFunc()) { this.Close(); } } } Which errors in Main(), here: static void Main() { ... // Following line errors Application.Run(new MyForm()); } I’ve tried checking the result of MyForm like this: static void Main() { ... MyForm frm = new MyForm(); if (frm != null) { // Following line errors Application.Run(frm); } } But that doesn’t seem to help. Can anyone tell me a way around this, please? Maybe a way to check the form to see if it still exists?

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• C# Constructor Problem When Using Generics

  - by Jimbo

  Please see an example of my code below: public class ScrollableCheckboxList { public List<ScrollableCheckboxItem> listitems; public void ScrollableCheckboxList<TModel>(IEnumerable<TModel> items, string valueField, string textField, string titleField) where TModel : class { listitems = new List<ScrollableCheckboxItem>(); foreach (TModel item in items) { Type t = typeof(TModel); PropertyInfo[] props = new [] { t.GetProperty(textField), t.GetProperty(valueField), t.GetProperty(titleField) }; listitems.Add(new ScrollableCheckboxItem { text = props[0].GetValue(item, null).ToString(), value = props[1].GetValue(item, null).ToString(), title = props[2].GetValue(item, null).ToString() }); } } } The code produces the following error: 'ScrollableCheckboxList': member names cannot be the same as their enclosing type This clearly means that there is a method in the class that has the same name as the class, but usually insinuates that the method is trying to return something (which is not allowed) In my case, all I have done is declare a constructor - why would this be a problem?

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• Copy Constructor in C++

  - by user265260

  i have this code #include <iostream> using namespace std; class Test{ public: int a; Test(int i=0):a(i){} ~Test(){ cout << a << endl; } Test(const Test &){ cout << "copy" << endl; } void operator=(const Test &){ cout << "=" << endl; } Test operator+(Test& p){ Test res(a+p.a); return res; } }; int main (int argc, char const *argv[]){ Test t1(10), t2(20); Test t3=t1+t2; return 0; } Output: 30 20 10 Why isnt the copy constructor called here?

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• Constructor Definition

  - by mctl87

  Ok so i have a class Vector: #include <cstdlib> class Vec { private: size_t size; int * ptab; public: Vec(size_t n); ~Vec() {delete [] ptab;} size_t size() const {return size;} int & operator[](int n) {return ptab[n];} int operator[](int n) const {return ptab[n];} void operator=(Vec const& v); }; inline Vec::Vec(size_t n) : size(n), ptab(new int[n]) { } and the problem is that in one of my homework exercises i have to extend constructor def, so all elements will be initialized with zeros. I thought i know the basics but cant get through this dynamic array -.- ps. sry for gramma and other mistakes ;)

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• What are the default mount settings for mount / fstab?

  - by John Craick

  What are the default mounting options for a non root partition ? The man entry for mount says ... defaults - use default options: rw, suid, dev, exec, auto, nouser, and async. ... so that might be what we expect to see. But, unless I'm missing something, that's not what happens. I have an ext3 partition labelled "NewHome20G" which is seen as /dev/sdc6 by the system. This we can see from ... root@john-pc1204:~# blkid | grep NewHome20G /dev/sdc6: LABEL="NewHome20G" UUID="d024bad5-906c-46c0-b7d4-812daf2c9628" TYPE="ext3" I have an entry in fstab as follows ... root@john-pc1204:~# cat /etc/fstab | grep NewHome LABEL=NewHome20G /media/NewHome20G ext3 rw,nosuid,nodev,exec,users 0 2 Note the option settings that are specified in that fstab line. Now I look at how the partition is actually mounted after boot up ... root@john-pc1204:~# mount -l | grep sdc6 /dev/sdc6 on /media/NewHome20G type ext3 (rw,noexec,nosuid,nodev) [NewHome20G] ... so, when the filesystem gets mounted the exec & users options I specified seem to have been ignored. Just to be sure, I unmount sdc6, remount it and look at the mount options again ... root@john-pc1204:~# umount /dev/sdc6 root@john-pc1204:~# mount /dev/sdc6 root@john-pc1204:~# mount -l | grep sdc6 /dev/sdc6 on /media/NewHome20G type ext3 (rw,noexec,nosuid,nodev) [NewHome20G] .... same result Now I unmount the partition again, remount it specifying the exec option and look at the result ... root@john-pc1204:~# umount /dev/sdc6 root@john-pc1204:~# mount /dev/sdc6 -o exec root@john-pc1204:~# mount -l | grep sdc6 /dev/sdc6 on /media/NewHome20G type ext3 (rw,nosuid,nodev) [NewHome20G] ... and here the exec option has finally taken effect and the noexec setting has vanished. Just for interest, I re-mount the partition with the defaults option root@john-pc1204:~# umount /dev/sdc6 root@john-pc1204:~# mount /dev/sdc6 -o defaults root@john-pc1204:~# mount -l | grep sdc6 /dev/sdc6 on /media/NewHome20G type ext3 (rw,noexec,nosuid,nodev) [NewHome20G] The noexec is back, so it looks very like rw,noexec,nosuid,nodev are the default options which is NOT what man says. Why does this matter ? I have a folder full of useful scripts stored on a data disk. Because that disk is mounted noexec those scripts won't run, even though they have all been set with chmod 777. I can work round this in several ways but it's disappointing that the man entry seems to be wrong. Have I missed something obvious here or have the default options in Ubuntu changed from what they were a few versions ago ?

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• How do I make Geany my default editor on Ubuntu?

  - by Programming Noob

  I actually want to change the default text editor on my Ubuntu 12.04 from nano to Geany. When I used this code: update-alternatives --config editor .. I don't see Geany in the list. So to add Geany, this is supposed to work right? update-alternatives --install /usr/bin/geany geany /usr/bin/geany 10 Also, on a side note, can you tell me if you would personally suggest me to change the default editor from nano to Geany, and why?

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• Multiple Default Routes in ASP.NET MVC to different Default Actions

  - by Alex

  I have multiple controllers with different actions (no "Index" actions). The actions I consider "default" actions, are named differently. I want to create default routes for their names and have the first available action (from my list of default actions) executed if only the controller name is provided in the route. So, for example, I have the following actions which I want to consider default and want checked for their existence in a controller in this order: List() Draw() ViewSingle() The routing should somehow search for /{controller} and then take the first available action from the list above as default action, e.g.: /ControllerA -> ControllerA.List() /ControllerB -> ControllerB.Draw() /ControllerC -> ControllerC.ViewSingle() /ControllerD -> ControllerD.Draw() /ControllerE -> ControllerE.List() Is this possible? I tried creating additional Default actions like this but couldn't get it to work: routes.MapRoute("Default1", "{controller}/{action}", new { controller = UrlParameter.Optional, action = "List" } routes.MapRoute("Default2", "{controller}/{action}", new { controller = UrlParameter.Optional, action = "Draw" } routes.MapRoute("Default3", "{controller}/{action}", new { controller = UrlParameter.Optional, action = "ViewSingle" } Help?

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• SQL Design: representing a default value with overrides?

  - by Mark Harrison

  I need a sparse table which contains a set of "override" values for another table. I also need to specify the default value for the items overridden. For example, if the default value is 17, then foo,bar,baz will have the values 17,21,17: table "things" table "xvalue" name stuff name xval ---- ----- ---- ---- foo ... bar 21 bar ... baz ... If I don't care about a FK from xvalue.name - things.name, I could simply put a "DEFAULT" name: table "xvalue" name xval ---- ---- DEFAULT 17 bar 21 But I like having a FK. I could have a separate default table, but it seems odd to have 2x the number of tables. table "xvalue_default" xval ---- 17 table "xvalue" name xval ---- ---- bar 21 I could have a "defaults table" tablename attributename defaultvalue xvalue xval 17 but then I run into type issues on defaultvalue. My operations guys prefer as compact a representation as possible, so they can most easily see the "diff" or deviations from the default. What's the best way to represent this, including the default value? This will be for Oracle 10.2 if that makes a difference.

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• Change the default program for a filetype to something not in "Program Files" in Windows Vista

  - by Carson Myers

  I'm trying to make my python scripts run in python 2.6 by default when run from the command line. This is paired with adding certain scripts to the PATH variable and .py to PATHEXT for convenience. But I'll be damned if I can get the file type association to work. In the default programs dialog (found in control panel) I find .py, and click "Change Program." This gives me the same dialog as clicking "Open with..." on a file's context menu. I search for python. Tell it to use python, but it doesn't add it to the list of programs I am allowed to use. I tried making a shortcut to python in Program Files, but that won't work either. If I copy python into a folder in Program Files, then that works. But why can't I just point it at C:\python26\python.exe (which is in the PATH variable) in the first place? Is there a way around this, or do I have to just reinstall python into Program Files?

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• Default Gateway solution on NAT'd network (best options)

  - by kwiksand

  I've recently changed a network from a bunch of machines exposed to the net on a network to a more security conscious Firewall-fronted network with a DMZ for public services. Everything's mostly working perfectly now, but I've got the old problem of NAT Loopback where a machine within the LAN wants to access a public service via the public/external IP. I've solved this problem previously in a small/SOHO environment simply using NAT loopback features of the router in use or a simple iptables rule to do the same, but I want to make sure I make the most resilient choice with the least concern. It seems I can: Use iptables as I've said to DNAT and MASQUERADE the change source/destination so the connection works correctly i.e iptables -A PREROUTING -t nat -d ip.of.eth0.here -p tcp --dport 8080 -j DNAT --to 192.168.0.201:8080 iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -p tcp --dport 8080 -d 192.168.0.201 -j MASQUERADE Use split DNS, with internal mappings for public IP's Potentially do some route nastyness by setting the Default Gateway to use a different externally exposed IP to then come back in the public route (messy) Someone mentioned putting the Default Gateway within the DMZ as well (on serverfault), but I can't find the post again. I'm sure this is a common issue for many with NAT'd networks, but I've not really seen the perfect solve all when it comes to fixing this problem. What is your opinion?

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• Set default tab url in firefox 14

  - by sebster

  In the latest firefox update, new tabs show -instead of the previously default blank page- a window of recently viewed pages. Before this was available, I had installed an 'addon' to allow this (called 'fvd speed dial'). It worked fine however I have since delete.d this as it is no longer needed but still loads the page where the addon was housed:'chrome://fvd.speeddial/content/fvd_about_blank.html'. I have reinstalled firefox yet the same problem still occurs. On the 'about:config' page I have found the setting 'browser.newtab.url' but do not know the default url. Is there any way to remedy this? I will just add, I appologise if this is not the case with the new tab feature. It is all I have gathered from the firefox update page. Also, I do not want to, ideally, simply restore my settings as I have changed some of them (such as the search bar, that work fine. I am on windows-xp, home edition. Not sure of what service pack.

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• Where does Windows 8 put the exe of the default browser for Modern UI?

  - by avirk

  I was trying to some hack with Win-8 and I found something which is really gonna out my mind. When I set the default browser to the IE then its icon become Modern UI and I can't see the option Open file location at the bottom when I select it by right click. But if I don't set it default then it became a desktop version icon and show up the option when I select it. Same is for the Google Chrome when I checked it. IE icon when it is not set to default, I can see the option open file location. Google Chrome icon when it is set to default. Google Chrome of desktop version when it is set to default. So my question is where does Modern UI keep exe of the default browser? And why the default browser has Modern UI icon and non-default browser has desktop version icon.

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• CA2000 passing object reference to base constructor in C#

  - by Timothy

  I receive a warning when I run some code through Visual Studio's Code Analysis utility which I'm not sure how to resolve. Perhaps someone here has come across a similar issue, resolved it, and is willing to share their insight. I'm programming a custom-painted cell used in a DataGridView control. The code resembles: public class DataGridViewMyCustomColumn : DataGridViewColumn { public DataGridViewMyCustomColumn() : base(new DataGridViewMyCustomCell()) { } It generates the following warning: CA2000 : Microsoft.Reliability : In method 'DataGridViewMyCustomColumn.DataGridViewMyCustomColumn()' call System.IDisposable.Dispose on object 'new DataGridViewMyCustomCell()' before all references to it are out of scope. I understand it is warning me DataGridViewMyCustomCell (or a class that it inherits from) implements the IDisposable interface and the Dispose() method should be called to clean up any resources claimed by DataGridViewMyCustomCell when it is no longer. The examples I've seen on the internet suggest a using block to scope the lifetime of the object and have the system automatically dispose it, but base isn't recognized when moved into the body of the constructor so I can't write a using block around it... which I'm not sure I'd want to do anyway, since wouldn't that instruct the run time to free the object which could still be used later inside the base class? My question then, is the code okay as is? Or, how could it be refactored to resolve the warning? I don't want to suppress the warning unless it is truly appropriate to do so.

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• Temporary non-const istream reference in constructor (C++)

  - by Christopher Bruns

  It seems that a constructor that takes a non-const reference to an istream cannot be constructed with a temporary value in C++. #include <iostream> #include <sstream> using namespace std; class Bar { public: explicit Bar(std::istream& is) {} }; int main() { istringstream stream1("bar1"); Bar bar1(stream1); // OK on all platforms // compile error on linux, Mac gcc; OK on Windows MSVC Bar bar2(istringstream("bar2")); return 0; } This compiles fine with MSVC, but not with gcc. Using gcc I get a compile error: g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:18: error: no matching function for call to ‘Bar::Bar(std::istringstream)’ test.cpp:9: note: candidates are: Bar::Bar(std::istream&) test.cpp:7: note: Bar::Bar(const Bar&) Is there something philosophically wrong with the second way (bar2) of constructing a Bar object? It looks nicer to me, and does not require that stream1 variable that is only needed for a moment.

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• Enums, Constructor overloads with similar conversions.

  - by David Thornley

  Why does VisualC++ (2008) get confused 'C2666: 2 overloads have similar conversions' when I specify an enum as the second parameter, but not when I define a bool type? Shouldn't type matching already rule out the second constructor because it is of a 'basic_string' type? #include <string> using namespace std; enum EMyEnum { mbOne, mbTwo }; class test { public: #if 1 // 0 = COMPILE_OK, 1 = COMPILE_FAIL test(basic_string<char> myString, EMyEnum myBool2) { } test(bool myBool, bool myBool2) { } #else test(basic_string<char> myString, bool myBool2) { } test(bool myBool, bool myBool2) { } #endif }; void testme() { test("test", mbOne); } I can work around this by specifying a reference 'ie. basic_string &myString' but not if it is 'const basic_string &myString'. Also calling explicitly via "test((basic_string)"test", mbOne);" also works. I suspect this has something to do with every expression/type being resolved to a bool via an inherent '!=0'. Curious for comments all the same :)

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• Ruby - calling constructor without arguments & removal of new line characters

  - by Raj

  I am a newbie at Ruby, I have written down a sample program. I dont understand the following: Why constructor without any arguments are not called in Ruby? How do we access the class variable outside the class' definition? Why does it always append newline characters at the end of the string? How do we strip it? Code: class Employee attr_reader :empid attr_writer :empid attr_writer :name def name return @name.upcase end attr_accessor :salary @@employeeCount = 0 def initiaze() @@employeeCount += 1 puts ("Initialize called!") end def getCount return @@employeeCount end end anEmp = Employee.new print ("Enter new employee name: ") anEmp.name = gets() print ("Enter #{anEmp.name}'s employee ID: ") anEmp.empid = gets() print ("Enter salary for #{anEmp.name}: ") anEmp.salary = gets() theEmpName = anEmp.name.split.join("\n") theEmpID = anEmp.empid.split.join("\n") theEmpSalary = anEmp.salary.split.join("\n") anEmp = Employee.new() anEmp = Employee.new() theCount = anEmp.getCount puts ("New employee #{theEmpName} with employee ID #{theEmpID} has been enrolled, welcome to hell! You have been paid as low as $ #{theEmpSalary}") puts ("Total number of employees created = #{theCount}") Output: Enter new employee name: Lionel Messi Enter LIONEL MESSI 's employee ID: 10 Enter salary for LIONEL MESSI : 10000000 New employee LIONEL MESSI with employee ID 10 has been enrolled, welcome to hell! You have been paid as low as $ 10000000 Total number of employees created = 0 Thanks

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• stealing inside the move constructor

  - by FredOverflow

  During the implementation of the move constructor of a toy class, I noticed a pattern: array2D(array2D&& that) { data_ = that.data_; that.data_ = 0; height_ = that.height_; that.height_ = 0; width_ = that.width_; that.width_ = 0; size_ = that.size_; that.size_ = 0; } The pattern obviously being: member = that.member; that.member = 0; So I wrote a preprocessor macro to make stealing less verbose and error-prone: #define STEAL(member) member = that.member; that.member = 0; Now the implementation looks as following: array2D(array2D&& that) { STEAL(data_); STEAL(height_); STEAL(width_); STEAL(size_); } Are there any downsides to this? Is there a cleaner solution that does not require the preprocessor?

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• Inheritance and choose constructor from base class

  - by myle

  My question is rather simple, but I am stuck. How can I choose the desired constructor from base class? // node.h #ifndef NODE_H #define NODE_H #include <vector> // definition of an exception-class class WrongBoundsException { }; class Node { public: ... Node(double, double, std::vector<double>&) throw (WrongBoundsException); ... }; #endif // InternalNode.h #ifndef INTERNALNODE_H #define INTERNALNODE_H #include <vector> #include "Node.h" class InternalNode : public Node { public: // the position of the leftmost child (child left) int left_child; // the position of the parent int parent; InternalNode(double, double, std::vector<double>&, int parent, int left_child) throw (WrongBoundsException); private: int abcd; }; #endif // InternalNode.cpp #include "InternalNode.h" #define UNDEFINED_CHILD -1 #define ROOT -1 // Here is the problem InternalNode::InternalNode(double a, double b, std::vector<double> &v, int par, int lc) throw (WrongBoundsException) : Node(a, b, v), parent(par), left_child(lc) { std::cout << par << std::endl; } I get: $ g++ InternalNode.cpp InternalNode.cpp:16: error: declaration of ‘InternalNode::InternalNode(double, double, std::vector &, int, int) throw (WrongBoundsException)’ throws different exceptions InternalNode.h:17: error: from previous declaration ‘InternalNode::InternalNode(double, double, std::vector &, int, int)’ UPDATE 0: Fixed missing : UPDATE 1: Fixed throw exception

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• Copy constructor demo (crashing...)

  - by AKN

  Here is the program... class CopyCon { public: char *name; CopyCon() { name = new char; } CopyCon(const CopyCon &objCopyCon) { name = new char; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete name; name = NULL; } } }; int main() { CopyCon objCopyCon1; objCopyCon1.name = "Hai"; CopyCon objCopyCon2(objCopyCon1); objCopyCon1.name = "Hello"; cout<<objCopyCon2.name<<endl; return 0; } Once the code execution completes, when the destructor called, it crashes on 'delete' saying... Debug Error! Program: ... HEAP CORRUPTION DETECTED: after Normal block (#124) at 0x00366990. CRT detected that the application wrote to memory after end of heap buffer. (Press Retry to debug the application) Don't we have to clear the heap memory in destructor. What's wrong with this program? Pls someone help! Copy constructor works perfectly as intended. But still... !?

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• Should a C++ constructor do real work?

  - by Wade Williams

  I'm strugging with some advice I have in the back of my mind but for which I can't remember the reasoning. I seem to remember at some point reading some advice (can't remember the source) that C++ constructors should not do real work. Rather, they should initialize variables only. The advice when on to explain that real work should be done in some sort of init() method, to be called separately after the instance was created. The situation is I have a class that represents a hardware device. It makes logical sense to me for the constructor to call the routines that query the device in order to build up the instance variables that describe the device. In other words, once new instantiates the object, the developer receives an object which is ready to be used, no separate call to object-init() required. Is there a good reason why constructors shouldn't do real work? Obviously it could slow allocation time, but that wouldn't be any different if calling a separate method immediately after allocation. Just trying to figure out what gotchas I not currently considering that might have lead to such advice.

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• Is it bad practise to initialise fields outside of an explicit constructor

  - by MrTortoise

  So its monday and we are arguing about coding practises. The examples here are a litttle too simple, but the real deal has several constructors. In order to initialise the simple values (eg dates to their min value) I have moved the code out of the constructors and into the field definitions. public class ConstructorExample { string _string = "John"; } public class ConstructorExample2 { string _string; public ConstructorExample2() { _string = "John"; } } How should it be done by the book. I tend to be very case by case and so am maybe a little lax abotu this kind of thing. However i feel that accams razor tells me to move the initialisation out of multiple constructors. Of course I could always move this shared initialisation into a private method. The question is essentially ... is initialising fields where they are defined as opposed to the constructor bad in any way? The argument I am facing is one of error handling, but i do not feel it is relevant as there are no possible exceptions that won't be picked up at compile time.

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