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• Why does Sql Server recommends creating an index when it already exist?

  - by Pierre-Alain Vigeant

  I ran a very basic query against one of our table and I noticed that the execution plan query processor is recommending that we create an index on a column The query is SELECT SUM(DATALENGTH(Data)) FROM Item WHERE Namespace = 'http://some_url/some_namespace/' After running, I get the following message // The Query Processor estimates that implementing the following index could improve the query cost by 96.7211%. CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>] ON [dbo].[Item] ([Namespace]) My problem is that I already have such index on that column: CREATE NONCLUSTERED INDEX [IX_ItemNamespace] ON [dbo].[Item] ( [Namespace] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] Why is Sql Server recommending me to create such index when it already exist?

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• How to analyze Heap Dumps

  - by Deeja

  Hi Guys, I am successful in generating Heap Dumps of my application machine but I do not know how to analyze it. Can someone tell me how to? Thanks and Regards, Deepti

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• Ways to calculate similarity

  - by MarySheen

  Hi I am doing a community website that requires me to calculate the similarity between any two users. each user is described with the following attributes: age, skin type (oily, dry), hair type (long, short, medium), lifestyle (active outdoor lover, TV junky) and others. Can anyone tell me how to go about this problem or point me to some resources. Thanks Mary

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• What is better: Developing a Web project in MVC or N -Tier Architecture?

  - by Starx

  I have asked a similar question before and got an convincing answer as well? http://stackoverflow.com/questions/2843311/what-is-difference-of-developing-a-website-in-mvc-and-3-tier-or-n-tier-architectu Due to the conclusion of this question I started developing projects in N-tier Architecture. Just about an hour ago, I asked another question, about what is the best design pattern to create interface? There the most voted answer is suggesting me to use MVC architecture. http://stackoverflow.com/questions/2930300/what-is-the-best-desing-pattern-to-design-the-interface-of-an-webpage Now I am confused, First post suggested me that both are similar, just a difference that in N-tier, the tier are physically and logically separated and one layer has access to the one above and below it but not all the layers. I think ASP.net used 3 Tier architecture while developing applications or Web applications. Where as frameworks like Zend, Symphony they use MVC. I just want to stick to a pattern that is best suitable for WebProject Development? May be this is a very silly confusion? But if someone could clear this confusion, that would be very greatful?

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• Singleton design potential leak

  - by iBrad Apps

  I have downloaded a library off of github and have noticed that in the main singleton of the library there is a possible leak in this bit of code: +(DDGameKitHelper*) sharedGameKitHelper { @synchronized(self) { if (instanceOfGameKitHelper == nil) { [[DDGameKitHelper alloc] init]; } return instanceOfGameKitHelper; } return nil; } Now obviously there is no release or autorelease anywhere so I must do it but how and in what way properly? I have looked at various Singleton design patterns on the Internet and they just assign, in this case, instanceOfGameKitHelper to the alloc and init line. Anyway how would I properly fix this? Thanks!

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• BGP Multihomed/Multi-location best practice

  - by Tom O'Connor

  We're in the process of designing a new iteration of our network where we improve resilliency by adding a second datacentre. We'll be adding a second datacentre, with an identical configuration of servers as our primary location. To achieve network connectivity, we're looking into a couple of possible methods. See earlier questions http://serverfault.com/questions/86736/best-way-to-improve-resilience and http://serverfault.com/questions/101582/dns-round-robin-failover-and-load-balancing I'm pretty convinced that BGP is the right way to go about this, and this question is not about RRDNS. 1) If we have 2 locations, do we announce the same IP address block from both locations? 2) If we did this, but had a management ssh interface on x.x.x.50 from datacentre A, but it was on x.x.x.150 in datacentre B. What is the best practice mechanism for achieving this? Because if I were nearest to A, then all my traffic would go to x.50, but if i attempted to connect to x.150, I'd not be able to connect, because this address wouldn't be valid at A, but only at B. Is the best solution to announce 2 different netblocks, one at each location, facilitating the need for RRDNS, or to announce a single block, and run some form of VPN between the two sites for managment traffic?

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• How to populate a generic list of objects in C# from SQL database

  - by developr

  I am just learning ASP.NET c# and trying to incorporate best practices into my applications. Everything that I read says to layer my applications into DAL, BLL, UI, etc based on separation of concerns. Instead of passing datatables around, I am thinking about using custom objects so that I am loosely coupled to my data layer and can take advantage of intellisense in VS. I assume these objects would be considered DTOs? First, where do these objects reside in my layers? BLL, DAL, other? Second, when populating from SQL, should I loop through a data reader to populate the list or first fill a data table, then loop through the table to populate the list? I know you should close the database connection as soon as possible, but it seems like even more overhead to populate the data table and then loop through that for the list. Third, everything I see these days says use Linq2SQL. I am planning to learn Linq2SQL, but at this time I am working with a legacy database that doesn't have foreign keys setup and I do not have the ability to fix it atm. Also, I want to learn more about c# before I start getting into ORM solutions like nHibernate. At the same time I don't want to type out all the connection and SQL plumbing for every query. Is it ok to use the Enterprise DAAB for now?

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• Logic inside an enum

  - by Vivin Paliath

  My colleagues and I were having a discussion regarding logic in enums. My personal preference is to not have any sort of logic in Java enums (although Java provides the ability to do that). The discussion in this cased centered around having a convenience method inside the enum that returned a map: public enum PackageTypes { Letter("01", "Letter"), .. .. Tube("02", "Packaging Tube"); private String packageCode; private String packageDescription; .. .. public static Map<String, String> toMap() { Map<String, String> map = new LinkedHashMap<String, String>(); for(PackageType packageType : PackageType.values()) { map.put(packageType.getPackageCode(), packageType.getPackageDescription()); } return map; } } My personal preference is to pull this out into a service. The argument for having the method inside the enum centered around convenience. The idea was that you don't have to go to a service to get it, but can query the enum directly. My argument centered around separation of concern and abstracting any kind of logic out to a service. I didn't think "convenience" was a strong argument to put this method inside an enum. From a best-practices perspective, which one is better? Or does it simply come down to a matter of personal preference and code style?

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• Help improving a simple assembly function

  - by MPelletier

  I just handed in this function in an assignment. It is done (hence no homework tag). But I would like to see how this can be improved. Essentially, the function sums the squares of all the integers between 1 and the given number, using the following formula: n(n+1)(2n+1)/6 Where n is the maximum number. The function below is made to catch any overflow and return 0 should any occur. UInt32 sumSquares(const UInt32 number) { int result = 0; __asm { mov eax, number //move number in eax mov edx, 2 //move 2 in edx mul edx //multiply (2n) jo end //jump to end if overflow add eax, 1 //addition (2n+1) jo end //jump to end if overflow mov ecx, eax //move (2n+1) in ecx mov ebx, number //move number in ebx add ebx, 1 //addition (n+1) jo end //jump to end if overflow mov eax, number //move number in eax for multiplication mul ebx //multiply n(n+1) jo end //jump to end if overflow mul ecx //multiply n(n+1)(2n+1) jo end //jump to end if overflow mov ebx, 6 //move 6 in ebx div ebx //divide by 6, the result will be in eax mov result, eax //move eax in result end: } return result; } Basically, I want to know what I can improve in there. In terms of best-practices mostly. One thing sounds obvious: smarter overflow check (with a single check for whatever maximum input would cause an overflow).

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• Proper way to implement IXmlSerializable?

  - by Greg

  Once a programmer decides to implement IXmlSerializable, what are the rules and best practices for implementing it? I've heard that GetSchema() should return null and ReadXml should move to the next element before returning. Are these true? And what about WriteXml: should it write a root element for the object or is it assumed that the root is already written? How should child objects be treated and written. Here's a sample of what I have now. I'll update it as I get good responses. public class Calendar: IEnumerable<Gvent>, IXmlSerializable { public XmlSchema GetSchema() { return null; } public void ReadXml(XmlReader reader) { if (reader.MoveToContent() == XmlNodeType.Element && reader.LocalName == "Calendar") { _Name = reader["Name"]; _Enabled = Boolean.Parse(reader["Enabled"]); _Color = Color.FromArgb(Int32.Parse(reader["Color"])); if (reader.ReadToDescendant("Event")) { while (reader.MoveToContent() == XmlNodeType.Element && reader.LocalName == "Event") { var evt = new Event(); evt.ReadXml(reader); _Events.Add(evt); } } reader.Read(); } } public void WriteXml(XmlWriter writer) { writer.WriteAttributeString("Name", _Name); writer.WriteAttributeString("Enabled", _Enabled.ToString()); writer.WriteAttributeString("Color", _Color.ToArgb().ToString()); foreach (var evt in _Events) { writer.WriteStartElement("Event"); evt.WriteXml(writer); writer.WriteEndElement(); } } } public class Event : IXmlSerializable { public XmlSchema GetSchema() { return null; } public void ReadXml(XmlReader reader) { if (reader.MoveToContent() == XmlNodeType.Element && reader.LocalName == "Event") { _Title = reader["Title"]; _Start = DateTime.FromBinary(Int64.Parse(reader["Start"])); _Stop = DateTime.FromBinary(Int64.Parse(reader["Stop"])); reader.Read(); } } public void WriteXml(XmlWriter writer) { writer.WriteAttributeString("Title", _Title); writer.WriteAttributeString("Start", _Start.ToBinary().ToString()); writer.WriteAttributeString("Stop", _Stop.ToBinary().ToString()); } }

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• Nested dereferencing arrows in Perl: to omit or not to omit?

  - by DVK

  In Perl, when you have a nested data structure, it is permissible to omit de-referencing arrows to 2d and more level of nesting. In other words, the following two syntaxes are identical: my $hash_ref = { 1 => [ 11, 12, 13 ], 3 => [31, 32] }; my $elem1 = $hash_ref->{1}->[1]; my $elem2 = $hash_ref->{1}[1]; # exactly the same as above Now, my question is, is there a good reason to choose one style over the other? It seems to be a popular bone of stylistic contention (Just on SO, I accidentally bumped into this and this in the space of 5 minutes). So far, none of the usual suspects says anything definitive: perldoc merely says "you are free to omit the pointer dereferencing arrow". Conway's "Perl Best Practices" says "whenever possible, dereference with arrows", but it appears to only apply to the context of dereferencing the main reference, not optional arrows on 2d level of nested data structures. "MAstering Perl for Bioinfirmatics" author James Tisdall doesn't give very solid preference either: "The sharp-witted reader may have noticed that we seem to be omitting arrow operators between array subscripts. (After all, these are anonymous arrays of anonymous arrays of anonymous arrays, etc., so shouldn't they be written [$array-[$i]-[$j]-[$k]?) Perl allows this; only the arrow operator between the variable name and the first array subscript is required. It make things easier on the eyes and helps avoid carpal tunnel syndrome. On the other hand, you may prefer to keep the dereferencing arrows in place, to make it clear you are dealing with references. Your choice." Personally, i'm on the side of "always put arrows in, since itg's more readable and obvious tiy're dealing with a reference".

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• Correct OOP design without getters?

  - by kane77

  I recently read that getters/setters are evil and I have to say it makes sense, yet when I started learning OOP one of the first things I learned was "Encapsulate your fields" so I learned to create class give it some fields, create getters, setters for them and create constructor where I initialize these fields. And every time some other class needs to manipulate this object (or for instance display it) I pass it the object and it manipulate it using getters/setters. I can see problems with this approach. But how to do it right? For instance displaying/rendering object that is "data" class - let's say Person, that has name and date of birth. Should the class have method for displaying the object where some Renderer would be passed as an argument? Wouldn't that violate principle that class should have only one purpose (in this case store state) so it should not care about presentation of this object. Can you suggest some good resources where best practices in OOP design are presented? I'm planning to start a project in my spare time and I want it to be my learning project in correct OOP design..

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• Software development metrics and reporting

  - by David M

  I've had some interesting conversations recently about software development metrics, in particular how they can be used in a reasonably large organisation to help development teams work better. I know there have been Stack Overflow questions about which metrics are good to use - like this one, but my question is more about which metrics are useful to which stakeholders, and at what level of aggregation. As an example, my view is that code coverage is a useful metric in the following ways (and maybe others): For a team's own internal use when combined with other measurements. For facilitating/enabling/mentoring teams, where it might be instructive when considered on a team-by-team basis as a trend (e.g. if team A and B have coverage this month of 75 and 50, I'd be more concerned with team A than B if the previous month they'd had 80 and 40). For senior management when presented as an aggregated statistic across a number of teams or a whole department. But I don't think it's useful for senior management to see this on a team-by-team basis, as this encourages artifical attempts to bolster coverage with tests that merely exercise, rather than test, code. I'm in an organisation with a couple of levels in its management hierarchy, but where the vast majority of managers are technically minded and able (with many still getting their hands dirty). Some of the development teams are leading the way in driving towards agile development practices, but others lag, and there is now a serious mandate from the top for this to be the way the organisation works. A couple of us are starting a programme to encourage this. In this sort of an organisation, what sort of metrics do you think are useful, to whom, why, and at what level of aggregation? I don't want people to feel their performance is being assessed based on a metric that they can artificially influence; at the same time, the senior management are going to want some sort of evidence that progress is being made. What advice or caveats can you provide based on experience in your own organisations? EDIT We are definitely wanting to use metrics as a tool for organisational improvement not as a tool for individual performance measurement.

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• Why doesn't every class in the .Net framework have a corresponding interface?

  - by Thorsten Lorenz

  Since I started to develop in a test/behavior driven style, I appreciated the ability to mock out every dependency. Since mocking frameworks like Moq work best when told to mock an interface, I now implement an interface for almost every class I create b/c most likely I will have to mock it out in a test eventually. Well, and programming to an interface is good practice, anyways. At times, my classes take dependencies on .Net classes (e.g. FileSystemWatcher, DispatcherTimer). It would be great in that case to have an interface, so I could depend on an IDispatcherTimer instead, to be able to pass it a mock and simulate its behavior to see if my system under test reacts correctly. Unfortunately both of above mentioned classes do not implement such interfaces, so I have to resort to creating adapters, that do nothing else but inherit from the original class and conform to an interface, that I then can use. Here is such an adapter for the DispatcherTimer and the corresponding interface: using System; using System.Windows.Threading; public interface IDispatcherTimer { #region Events event EventHandler Tick; #endregion #region Properties Dispatcher Dispatcher { get; } TimeSpan Interval { get; set; } bool IsEnabled { get; set; } object Tag { get; set; } #endregion #region Public Methods void Start(); void Stop(); #endregion } /// <summary> /// Adapts the DispatcherTimer class to implement the <see cref="IDispatcherTimer"/> interface. /// </summary> public class DispatcherTimerAdapter : DispatcherTimer, IDispatcherTimer { } Although this is not the end of the world, I wonder, why the .Net developers didn't take the minute to make their classes implement these interfaces from the get go. It puzzles me especially since now there is a big push for good practices from inside Microsoft. Does anyone have any (maybe inside) information why this contradiction exists?

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• SQL Server CLR stored procedures in data processing tasks - good or evil?

  - by Gart

  In short - is it a good design solution to implement most of the business logic in CLR stored procedures? I have read much about them recently but I can't figure out when they should be used, what are the best practices, are they good enough or not. For example, my business application needs to parse a large fixed-length text file, extract some numbers from each line in the file, according to these numbers apply some complex business rules (involving regex matching, pattern matching against data from many tables in the database and such), and as a result of this calculation update records in the database. There is also a GUI for the user to select the file, view the results, etc. This application seems to be a good candidate to implement the classic 3-tier architecture: the Data Layer, the Logic Layer, and the GUI layer. The Data Layer would access the database The Logic Layer would run as a WCF service and implement the business rules, interacting with the Data Layer The GUI Layer would be a means of communication between the Logic Layer and the User. Now, thinking of this design, I can see that most of the business rules may be implemented in a SQL CLR and stored in SQL Server. I might store all my raw data in the database, run the processing there, and get the results. I see some advantages and disadvantages of this solution: Pros: The business logic runs close to the data, meaning less network traffic. Process all data at once, possibly utilizing parallelizm and optimal execution plan. Cons: Scattering of the business logic: some part is here, some part is there. Questionable design solution, may encounter unknown problems. Difficult to implement a progress indicator for the processing task. I would like to hear all your opinions about SQL CLR. Does anybody use it in production? Are there any problems with such design? Is it a good thing?

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• Database design for invoices, invoice lines & revisions

  - by FreshCode

  I'm designing the 2nd major iteration of a relational database for a franchise's CRM (with lots of refactoring) and I need help on the best database design practices for storing job invoices and invoice lines with a strong audit trail of any changes made to each invoice. Current schema Invoices Table InvoiceId (int) // Primary key JobId (int) StatusId (tinyint) // Pending, Paid or Deleted UserId (int) // auditing user Reference (nvarchar(256)) // unique natural string key with invoice number Date (datetime) Comments (nvarchar(MAX)) InvoiceLines Table LineId (int) // Primary key InvoiceId (int) // related to Invoices above Quantity (decimal(9,4)) Title (nvarchar(512)) Comment (nvarchar(512)) UnitPrice (smallmoney) Revision schema InvoiceRevisions Table RevisionId (int) // Primary key InvoiceId (int) JobId (int) StatusId (tinyint) // Pending, Paid or Deleted UserId (int) // auditing user Reference (nvarchar(256)) // unique natural string key with invoice number Date (datetime) Total (smallmoney) Schema design considerations 1. Is it sensible to store an invoice's Paid or Pending status? All payments received for an invoice are stored in a Payments table (eg. Cash, Credit Card, Cheque, Bank Deposit). Is it meaningful to store a "Paid" status in the Invoices table if all the income related to a given job's invoices can be inferred from the Payments table? 2. How to keep track of invoice line item revisions? I can track revisions to an invoice by storing status changes along with the invoice total and the auditing user in an invoice revision table (see InvoiceRevisions above), but keeping track of an invoice line revision table feels hard to maintain. Thoughts? 3. Tax How should I incorporate sales tax (or 14% VAT in SA) when storing invoice data?

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• Managing highly repetitive code and documentation in Java

  - by polygenelubricants

  Highly repetitive code is generally a bad thing, and there are design patterns that can help minimize this. However, sometimes it's simply inevitable due to the constraints of the language itself. Take the following example from java.util.Arrays: /** * Assigns the specified long value to each element of the specified * range of the specified array of longs. The range to be filled * extends from index <tt>fromIndex</tt>, inclusive, to index * <tt>toIndex</tt>, exclusive. (If <tt>fromIndex==toIndex</tt>, the * range to be filled is empty.) * * @param a the array to be filled * @param fromIndex the index of the first element (inclusive) to be * filled with the specified value * @param toIndex the index of the last element (exclusive) to be * filled with the specified value * @param val the value to be stored in all elements of the array * @throws IllegalArgumentException if <tt>fromIndex &gt; toIndex</tt> * @throws ArrayIndexOutOfBoundsException if <tt>fromIndex &lt; 0</tt> or * <tt>toIndex &gt; a.length</tt> */ public static void fill(long[] a, int fromIndex, int toIndex, long val) { rangeCheck(a.length, fromIndex, toIndex); for (int i=fromIndex; i<toIndex; i++) a[i] = val; } The above snippet appears in the source code 8 times, with very little variation in the documentation/method signature but exactly the same method body, one for each of the root array types int[], short[], char[], byte[], boolean[], double[], float[], and Object[]. I believe that unless one resorts to reflection (which is an entirely different subject in itself), this repetition is inevitable. I understand that as a utility class, such high concentration of repetitive Java code is highly atypical, but even with the best practice, repetition does happen! Refactoring doesn't always work because it's not always possible (the obvious case is when the repetition is in the documentation). Obviously maintaining this source code is a nightmare. A slight typo in the documentation, or a minor bug in the implementation, is multiplied by however many repetitions was made. In fact, the best example happens to involve this exact class: Google Research Blog - Extra, Extra - Read All About It: Nearly All Binary Searches and Mergesorts are Broken (by Joshua Bloch, Software Engineer) The bug is a surprisingly subtle one, occurring in what many thought to be just a simple and straightforward algorithm. // int mid =(low + high) / 2; // the bug int mid = (low + high) >>> 1; // the fix The above line appears 11 times in the source code! So my questions are: How are these kinds of repetitive Java code/documentation handled in practice? How are they developed, maintained, and tested? Do you start with "the original", and make it as mature as possible, and then copy and paste as necessary and hope you didn't make a mistake? And if you did make a mistake in the original, then just fix it everywhere, unless you're comfortable with deleting the copies and repeating the whole replication process? And you apply this same process for the testing code as well? Would Java benefit from some sort of limited-use source code preprocessing for this kind of thing? Perhaps Sun has their own preprocessor to help write, maintain, document and test these kind of repetitive library code? A comment requested another example, so I pulled this one from Google Collections: com.google.common.base.Predicates lines 276-310 (AndPredicate) vs lines 312-346 (OrPredicate). The source for these two classes are identical, except for: AndPredicate vs OrPredicate (each appears 5 times in its class) "And(" vs Or(" (in the respective toString() methods) #and vs #or (in the @see Javadoc comments) true vs false (in apply; ! can be rewritten out of the expression) -1 /* all bits on */ vs 0 /* all bits off */ in hashCode() &= vs |= in hashCode()

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• How can I cleanly turn a nested Perl hash into a non-nested one?

  - by knorv

  Assume a nested hash structure %old_hash .. my %old_hash; $old_hash{"foo"}{"bar"}{"zonk"} = "hello"; .. which we want to "flatten" (sorry if that's the wrong terminology!) to a non-nested hash using the sub &flatten(...) so that .. my %h = &flatten(\%old_hash); die unless($h{"zonk"} eq "hello"); The following definition of &flatten(...) does the trick: sub flatten { my $hashref = shift; my %hash; my %i = %{$hashref}; foreach my $ii (keys(%i)) { my %j = %{$i{$ii}}; foreach my $jj (keys(%j)) { my %k = %{$j{$jj}}; foreach my $kk (keys(%k)) { my $value = $k{$kk}; $hash{$kk} = $value; } } } return %hash; } While the code given works it is not very readable or clean. My question is two-fold: In what ways does the given code not correspond to modern Perl best practices? Be harsh! :-) How would you clean it up?

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• How to target multiple versions of .NET Framework from MSBuild?

  - by McKAMEY

  I am improving the builds for an open source project which currently supports .NET Framework v2.0, v3.5, and now v4.0. Up until now, I've restricted myself to v2.0 to ensure compatibility, but with VS2010 I am interested in having real targeted builds. I'm looking for some guidance on how to edit the MSBuild csproj/sln to be able to cleanly produce builds for each target. I'm willing to have complexity in the csproj and in a batch file to control the build. My goal is to be able to have a command line script that could produce the builds without needing Visual Studio installed, but only the necessary .NET Framework(s). Ideally, I'd like to minimize dependencies on additional software. I notice that a lot of people use NAnt (e.g. Ninject builds many targets with NAnt) but I'm unsure if this is necessary or if they are just more familiar with it. I'm pretty sure this can be done but am having trouble finding a definitive guide on setting it up and best practices. Bonus: my next step after getting this set up will be to better support Mono Framework. Any help on doing this same thing for Mono would be much appreciated.

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• use of assertions for type checking in php?

  - by user151841

  I do some checking of arguments in my classes in php using exception-throwing functions. I have functions that do a basic check ( ===, in_array etc ) and throw an exception on false. So I can do assertNumeric($argument, "\$argument is not numeric."); instead of if ( ! is_numeric($argument) ) { throw new Exception("\$argument is not numeric."); } Saves some typing I was reading in the comments of the php manual page on assert() that As noted on Wikipedia - "assertions are primarily a development tool, they are often disabled when a program is released to the public." and "Assertions should be used to document logically impossible situations and discover programming errors— if the 'impossible' occurs, then something fundamental is clearly wrong. This is distinct from error handling: most error conditions are possible, although some may be extremely unlikely to occur in practice. Using assertions as a general-purpose error handling mechanism is usually unwise: assertions do not allow for graceful recovery from errors, and an assertion failure will often halt the program's execution abruptly. Assertions also do not display a user-friendly error message." This means that the advice given by "gk at proliberty dot com" to force assertions to be enabled, even when they have been disabled manually, goes against best practices of only using them as a development tool So, am I 'doing it wrong'? What other/better ways of doing this are there?

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• Turning a nested hash structure into a non-nested hash structure - is this the cleanest way to do it

  - by knorv

  Assume a nested hash structure %old_hash .. my %old_hash; $old_hash{"foo"}{"bar"}{"zonk"} = "hello"; .. which we want to "flatten" (sorry if that's the wrong terminology!) to a non-nested hash using the sub &flatten(...) so that .. my %h = &flatten(\%old_hash); die unless($h{"zonk"} eq "hello"); The following definition of &flatten(...) does the trick: sub flatten { my $hashref = shift; my %hash; my %i = %{$hashref}; foreach my $ii (keys(%i)) { my %j = %{$i{$ii}}; foreach my $jj (keys(%j)) { my %k = %{$j{$jj}}; foreach my $kk (keys(%k)) { my $value = $k{$kk}; $hash{$kk} = $value; } } } return %hash; } While the code given works it is not very readable or clean. My question is two-fold: In what ways does the given code not correspond to modern Perl best practices? Be harsh! :-) How would you clean it up?

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• Java (or possibly other languages) learning path

  - by bgo

  I am familiar (as a self-learner) with C, python and php such that i can solve some problems involving simple steps (for example, i easily do calculations for physics lab reports with python which normally would take 4x-5x times longer with a calculator). The point here is, as doing such things, i learnt the idea / concepts of programming language and problem solving along with oop or fuctional programming etc. Recently i have started Java and, with the familiarity of other languages, i am doing well for starters but i need guidence. -I am thinking of learning syntax from sun java tutorials and then practicing with codingbat.com or similar sites. I need a reference book that i can study deeper aspects of the topics i am learning. What do you suggest about these? -The problem is (and always have been) the lack of practice. I need coding and problem-solving practices sources. I stuck at the point where i can't figure out what to do next. Can you suggest any source (possibly like codingbat)? If i could plan a learning trail, i can progress faster and efficiently. So i need ideas, comments, suggestions. Thanks in advance.

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• Generics vs inheritance (whenh no collection classes are involved)

  - by Ram

  This is an extension of this questionand probably might even be a duplicate of some other question(If so, please forgive me). I see from MSDN that generics are usually used with collections The most common use for generic classes is with collections like linked lists, hash tables, stacks, queues, trees and so on where operations such as adding and removing items from the collection are performed in much the same way regardless of the type of data being stored. The examples I have seen also validate the above statement. Can someone give a valid use of generics in a real-life scenario which does not involve any collections ? Pedantically, I was thinking about making an example which does not involve collections public class Animal<T> { public void Speak() { Console.WriteLine("I am an Animal and my type is " + typeof(T).ToString()); } public void Eat() { //Eat food } } public class Dog { public void WhoAmI() { Console.WriteLine(this.GetType().ToString()); } } and "An Animal of type Dog" will be Animal<Dog> magic = new Animal<Dog>(); It is entirely possible to have Dog getting inherited from Animal (Assuming a non-generic version of Animal)Dog:Animal Therefore Dog is an Animal Another example I was thinking was a BankAccount. It can be BankAccount<Checking>,BankAccount<Savings>. This can very well be Checking:BankAccount and Savings:BankAccount. Are there any best practices to determine if we should go with generics or with inheritance ?

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• Pass a data.frame column name to a function

  - by Kevin Middleton

  I'm trying to write a function to accept a data.frame (x) and a column from it. The function performs some calculations on x and later returns another data.frame. I'm stuck on the best-practices method to pass the column name to the function. The two minimal examples fun1 and fun2 below produce the desired result, being able to perform operations on x$column, using max() as an example. However, both rely on the seemingly (at least to me) inelegant (1) call to substitute() and possibly eval() and (2) the need to pass the column name as a character vector. fun1 <- function(x, column){ do.call("max", list(substitute(x[a], list(a = column)))) } fun2 <- function(x, column){ max(eval((substitute(x[a], list(a = column))))) } df <- data.frame(A = 1:20, B = rnorm(10)) fun1(df, "B") fun2(df, "B") I would like to be able to call the function as fun(df, B), for example. Other options I have considered but have not tried: Pass column as an integer of the column number. I think this would avoid substitute(). Ideally, the function could accept either. with(x, get(column)), but, even if it works, I think this would still require substitute Make use of formula() and match.call(), neither of which I have much experience with. Subquestion: Is do.call() preferred over eval()? Thanks, Kevin

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• Dependency Injection: How to maintain multiple configurations?

  - by Malax

  Hi StackOverflow, Lets assume we've build a system with a DI framework which is working quite fine. This system currently uses JMS to "talk" with other systems not maintained by us. The majority of our customers like the JMS approach and uses it according to our specification. The component which does all the messaging is injected with Spring into the rest of the application. Now we got the case that one customer cannot implement the JMS solution and want to use another messaging technology. Thats not a problem because we can simply implement a messaging service using this technology and inject it in the rest of the application. But how are we supposed to handle the deployment and maintenance of the configuration? Since the application uses Spring i could imagine to check in all the configurations i have for this application and the system administrator could start the application and passing the name of the DI XML file to specify which configuration should be loaded. But... it just don't feel right. Are there any solutions for such cases available? What are the best-practices you use? I could even imagine more complex scenarios which do not contain only one service substitution... Thanks a lot!

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