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  • Why enumerator structs are a really bad idea

    - by Simon Cooper
    If you've ever poked around the .NET class libraries in Reflector, I'm sure you would have noticed that the generic collection classes all have implementations of their IEnumerator as a struct rather than a class. As you will see, this design decision has some rather unfortunate side effects... As is generally known in the .NET world, mutable structs are a Very Bad Idea; and there are several other blogs around explaining this (Eric Lippert's blog post explains the problem quite well). In the BCL, the generic collection enumerators are all mutable structs, as they need to keep track of where they are in the collection. This bit me quite hard when I was coding a wrapper around a LinkedList<int>.Enumerator. It boils down to this code: sealed class EnumeratorWrapper : IEnumerator<int> { private readonly LinkedList<int>.Enumerator m_Enumerator; public EnumeratorWrapper(LinkedList<int> linkedList) { m_Enumerator = linkedList.GetEnumerator(); } public int Current { get { return m_Enumerator.Current; } } object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { return m_Enumerator.MoveNext(); } public void Reset() { ((System.Collections.IEnumerator)m_Enumerator).Reset(); } public void Dispose() { m_Enumerator.Dispose(); } } The key line here is the MoveNext method. When I initially coded this, I thought that the call to m_Enumerator.MoveNext() would alter the enumerator state in the m_Enumerator class variable and so the enumeration would proceed in an orderly fashion through the collection. However, when I ran this code it went into an infinite loop - the m_Enumerator.MoveNext() call wasn't actually changing the state in the m_Enumerator variable at all, and my code was looping forever on the first collection element. It was only after disassembling that method that I found out what was going on The MoveNext method above results in the following IL: .method public hidebysig newslot virtual final instance bool MoveNext() cil managed { .maxstack 1 .locals init ( [0] bool CS$1$0000, [1] valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator CS$0$0001) L_0000: nop L_0001: ldarg.0 L_0002: ldfld valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator EnumeratorWrapper::m_Enumerator L_0007: stloc.1 L_0008: ldloca.s CS$0$0001 L_000a: call instance bool [System]System.Collections.Generic.LinkedList`1/Enumerator::MoveNext() L_000f: stloc.0 L_0010: br.s L_0012 L_0012: ldloc.0 L_0013: ret } Here, the important line is 0002 - m_Enumerator is accessed using the ldfld operator, which does the following: Finds the value of a field in the object whose reference is currently on the evaluation stack. So, what the MoveNext method is doing is the following: public bool MoveNext() { LinkedList<int>.Enumerator CS$0$0001 = this.m_Enumerator; bool CS$1$0000 = CS$0$0001.MoveNext(); return CS$1$0000; } The enumerator instance being modified by the call to MoveNext is the one stored in the CS$0$0001 variable on the stack, and not the one in the EnumeratorWrapper class instance. Hence why the state of m_Enumerator wasn't getting updated. Hmm, ok. Well, why is it doing this? If you have a read of Eric Lippert's blog post about this issue, you'll notice he quotes a few sections of the C# spec. In particular, 7.5.4: ...if the field is readonly and the reference occurs outside an instance constructor of the class in which the field is declared, then the result is a value, namely the value of the field I in the object referenced by E. And my m_Enumerator field is readonly! Indeed, if I remove the readonly from the class variable then the problem goes away, and the code works as expected. The IL confirms this: .method public hidebysig newslot virtual final instance bool MoveNext() cil managed { .maxstack 1 .locals init ( [0] bool CS$1$0000) L_0000: nop L_0001: ldarg.0 L_0002: ldflda valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator EnumeratorWrapper::m_Enumerator L_0007: call instance bool [System]System.Collections.Generic.LinkedList`1/Enumerator::MoveNext() L_000c: stloc.0 L_000d: br.s L_000f L_000f: ldloc.0 L_0010: ret } Notice on line 0002, instead of the ldfld we had before, we've got a ldflda, which does this: Finds the address of a field in the object whose reference is currently on the evaluation stack. Instead of loading the value, we're loading the address of the m_Enumerator field. So now the call to MoveNext modifies the enumerator stored in the class rather than on the stack, and everything works as expected. Previously, I had thought enumerator structs were an odd but interesting feature of the BCL that I had used in the past to do linked list slices. However, effects like this only underline how dangerous mutable structs are, and I'm at a loss to explain why the enumerators were implemented as structs in the first place. (interestingly, the SortedList<TKey, TValue> enumerator is a struct but is private, which makes it even more odd - the only way it can be accessed is as a boxed IEnumerator!). I would love to hear people's theories as to why the enumerators are implemented in such a fashion. And bonus points if you can explain why LinkedList<int>.Enumerator.Reset is an explicit implementation but Dispose is implicit... Note to self: never ever ever code a mutable struct.

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  • C# return variables

    - by pb01
    In a debate regarding return variables, some members of the team prefer a method to return the result directly to the caller, whereas others prefer to declare a return variable that is then returned to the caller (see code examples below) The argument for the latter is that it allows a developer that is debugging the code to find the return value of the method before it returns to the caller thereby making the code easier to understand: This is especially true where method calls are daisy-chained. Are there any guidelines as to which is the most efficient and/or are there any other reasons why we should adopt one style over another? Thanks private bool Is2(int a) { return a == 2; } private bool Is3(int a) { var result = a == 3; return result; }

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  • Convert filenames to their checksum before saving to prevent duplicates. Is is a smart thing to do?

    - by Xananax
    TL;DR:what the title says I am developing some sort of image board in PHP. I was thinking of changing each image's filename to it's checksum prior to saving it. This way, I might be able to prevent duplicates. I know this wouldn't work for two images that are the same but differ in size or level of compression or whatnot, but this method would allow for an early check. What bugs me is that I never saw this method implemented anywhere, so I was wondering if there is a catch to it. Maybe it is just more efficient to keep the original filename and store the hash in DB? Maybe the whole method is just not useful and my question is moot? What do you think? On a side note, I don't really get how hashes are calculated so I was wondering, if my first question checks out, if it would be possible to calculate the likeness that two images are similar by comparing hashes (levenshtein or something of the sort).

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  • C#/.NET Little Wonders: Static Char Methods

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Often times in our code we deal with the bigger classes and types in the BCL, and occasionally forgot that there are some nice methods on the primitive types as well.  Today we will discuss some of the handy static methods that exist on the char (the C# alias of System.Char) type. The Background I was examining a piece of code this week where I saw the following: 1: // need to get the 5th (offset 4) character in upper case 2: var type = symbol.Substring(4, 1).ToUpper(); 3:  4: // test to see if the type is P 5: if (type == "P") 6: { 7: // ... do something with P type... 8: } Is there really any error in this code?  No, but it still struck me wrong because it is allocating two very short-lived throw-away strings, just to store and manipulate a single char: The call to Substring() generates a new string of length 1 The call to ToUpper() generates a new upper-case version of the string from Step 1. In my mind this is similar to using ToUpper() to do a case-insensitive compare: it isn’t wrong, it’s just much heavier than it needs to be (for more info on case-insensitive compares, see #2 in 5 More Little Wonders). One of my favorite books is the C++ Coding Standards: 101 Rules, Guidelines, and Best Practices by Sutter and Alexandrescu.  True, it’s about C++ standards, but there’s also some great general programming advice in there, including two rules I love:         8. Don’t Optimize Prematurely         9. Don’t Pessimize Prematurely We all know what #8 means: don’t optimize when there is no immediate need, especially at the expense of readability and maintainability.  I firmly believe this and in the axiom: it’s easier to make correct code fast than to make fast code correct.  Optimizing code to the point that it becomes difficult to maintain often gains little and often gives you little bang for the buck. But what about #9?  Well, for that they state: “All other things being equal, notably code complexity and readability, certain efficient design patterns and coding idioms should just flow naturally from your fingertips and are no harder to write then the pessimized alternatives. This is not premature optimization; it is avoiding gratuitous pessimization.” Or, if I may paraphrase: “where it doesn’t increase the code complexity and readability, prefer the more efficient option”. The example code above was one of those times I feel where we are violating a tacit C# coding idiom: avoid creating unnecessary temporary strings.  The code creates temporary strings to hold one char, which is just unnecessary.  I think the original coder thought he had to do this because ToUpper() is an instance method on string but not on char.  What he didn’t know, however, is that ToUpper() does exist on char, it’s just a static method instead (though you could write an extension method to make it look instance-ish). This leads me (in a long-winded way) to my Little Wonders for the day… Static Methods of System.Char So let’s look at some of these handy, and often overlooked, static methods on the char type: IsDigit(), IsLetter(), IsLetterOrDigit(), IsPunctuation(), IsWhiteSpace() Methods to tell you whether a char (or position in a string) belongs to a category of characters. IsLower(), IsUpper() Methods that check if a char (or position in a string) is lower or upper case ToLower(), ToUpper() Methods that convert a single char to the lower or upper equivalent. For example, if you wanted to see if a string contained any lower case characters, you could do the following: 1: if (symbol.Any(c => char.IsLower(c))) 2: { 3: // ... 4: } Which, incidentally, we could use a method group to shorten the expression to: 1: if (symbol.Any(char.IsLower)) 2: { 3: // ... 4: } Or, if you wanted to verify that all of the characters in a string are digits: 1: if (symbol.All(char.IsDigit)) 2: { 3: // ... 4: } Also, for the IsXxx() methods, there are overloads that take either a char, or a string and an index, this means that these two calls are logically identical: 1: // check given a character 2: if (char.IsUpper(symbol[0])) { ... } 3:  4: // check given a string and index 5: if (char.IsUpper(symbol, 0)) { ... } Obviously, if you just have a char, then you’d just use the first form.  But if you have a string you can use either form equally well. As a side note, care should be taken when examining all the available static methods on the System.Char type, as some seem to be redundant but actually have very different purposes.  For example, there are IsDigit() and IsNumeric() methods, which sound the same on the surface, but give you different results. IsDigit() returns true if it is a base-10 digit character (‘0’, ‘1’, … ‘9’) where IsNumeric() returns true if it’s any numeric character including the characters for ½, ¼, etc. Summary To come full circle back to our opening example, I would have preferred the code be written like this: 1: // grab 5th char and take upper case version of it 2: var type = char.ToUpper(symbol[4]); 3:  4: if (type == 'P') 5: { 6: // ... do something with P type... 7: } Not only is it just as readable (if not more so), but it performs over 3x faster on my machine:    1,000,000 iterations of char method took: 30 ms, 0.000050 ms/item.    1,000,000 iterations of string method took: 101 ms, 0.000101 ms/item. It’s not only immediately faster because we don’t allocate temporary strings, but as an added bonus there less garbage to collect later as well.  To me this qualifies as a case where we are using a common C# performance idiom (don’t create unnecessary temporary strings) to make our code better. Technorati Tags: C#,CSharp,.NET,Little Wonders,char,string

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  • Subterranean IL: Generics and array covariance

    - by Simon Cooper
    Arrays in .NET are curious beasts. They are the only built-in collection types in the CLR, and SZ-arrays (single dimension, zero-indexed) have their own commands and IL syntax. One of their stranger properties is they have a kind of built-in covariance long before generic variance was added in .NET 4. However, this causes a subtle but important problem with generics. First of all, we need to briefly recap on array covariance. SZ-array covariance To demonstrate, I'll tweak the classes I introduced in my previous posts: public class IncrementableClass { public int Value; public virtual void Increment(int incrementBy) { Value += incrementBy; } } public class IncrementableClassx2 : IncrementableClass { public override void Increment(int incrementBy) { base.Increment(incrementBy); base.Increment(incrementBy); } } In the CLR, SZ-arrays of reference types are implicitly convertible to arrays of the element's supertypes, all the way up to object (note that this does not apply to value types). That is, an instance of IncrementableClassx2[] can be used wherever a IncrementableClass[] or object[] is required. When an SZ-array could be used in this fashion, a run-time type check is performed when you try to insert an object into the array to make sure you're not trying to insert an instance of IncrementableClass into an IncrementableClassx2[]. This check means that the following code will compile fine but will fail at run-time: IncrementableClass[] array = new IncrementableClassx2[1]; array[0] = new IncrementableClass(); // throws ArrayTypeMismatchException These checks are enforced by the various stelem* and ldelem* il instructions in such a way as to ensure you can't insert a IncrementableClass into a IncrementableClassx2[]. For the rest of this post, however, I'm going to concentrate on the ldelema instruction. ldelema This instruction pops the array index (int32) and array reference (O) off the stack, and pushes a pointer (&) to the corresponding array element. However, unlike the ldelem instruction, the instruction's type argument must match the run-time array type exactly. This is because, once you've got a managed pointer, you can use that pointer to both load and store values in that array element using the ldind* and stind* (load/store indirect) instructions. As the same pointer can be used for both input and output to the array, the type argument to ldelema must be invariant. At the time, this was a perfectly reasonable restriction, and maintained array type-safety within managed code. However, along came generics, and with it the constrained callvirt instruction. So, what happens when we combine array covariance and constrained callvirt? .method public static void CallIncrementArrayValue() { // IncrementableClassx2[] arr = new IncrementableClassx2[1] ldc.i4.1 newarr IncrementableClassx2 // arr[0] = new IncrementableClassx2(); dup newobj instance void IncrementableClassx2::.ctor() ldc.i4.0 stelem.ref // IncrementArrayValue<IncrementableClass>(arr, 0) // here, we're treating an IncrementableClassx2[] as IncrementableClass[] dup ldc.i4.0 call void IncrementArrayValue<class IncrementableClass>(!!0[],int32) // ... ret } .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } And the result: Unhandled Exception: System.ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array. at IncrementArrayValue[T](T[] arr, Int32 index) at CallIncrementArrayValue() Hmm. We're instantiating the generic method as IncrementArrayValue<IncrementableClass>, but passing in an IncrementableClassx2[], hence the ldelema instruction is failing as it's expecting an IncrementableClass[]. On features and feature conflicts What we've got here is a conflict between existing behaviour (ldelema ensuring type safety on covariant arrays) and new behaviour (managed pointers to object references used for every constrained callvirt on generic type instances). And, although this is an edge case, there is no general workaround. The generic method could be hidden behind several layers of assemblies, wrappers and interfaces that make it a requirement to use array covariance when calling the generic method. Furthermore, this will only fail at runtime, whereas compile-time safety is what generics were designed for! The solution is the readonly. prefix instruction. This modifies the ldelema instruction to ignore the exact type check for arrays of reference types, and so it lets us take the address of array elements using a covariant type to the actual run-time type of the array: .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 readonly. ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } But what about type safety? In return for ignoring the type check, the resulting controlled mutability pointer can only be used in the following situations: As the object parameter to ldfld, ldflda, stfld, call and constrained callvirt instructions As the pointer parameter to ldobj or ldind* As the source parameter to cpobj In other words, the only operations allowed are those that read from the pointer; stind* and similar that alter the pointer itself are banned. This ensures that the array element we're pointing to won't be changed to anything untoward, and so type safety within the array is maintained. This is a typical example of the maxim that whenever you add a feature to a program, you have to consider how that feature interacts with every single one of the existing features. Although an edge case, the readonly. prefix instruction ensures that generics and array covariance work together and that compile-time type safety is maintained. Tune in next time for a look at the .ctor generic type constraint, and what it means.

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  • Check connection and reconnect wifi

    - by Ruud
    I'm building a wireless photoframe. The one thing I haven't been able to figure out is how to get my wifi connection back up using a recommended method. Right now I edited /etc/network/interfaces so wlan0 is started at boot: auto wlan0 iface wlan0 inet dhcp wireless-essid ourssid This method works fine for booting. But I found that if I do not check the connection for a long time (could be a week) it might be down. So I should reconnect. What I do now to verify the connection is working is downloading a file from the server that can't be cached (http://server.ext/ping.php?randomize=123456) If I fail to retrieve the file I assume that the connection is no longer working and I run a shell script like #!/bin/bash ifconfig wlan0 up iwconfig wlan0 essid "ourssid" dhclient wlan0 And the connection comes back. But I can't find anything if this is in any way a good method. Can this be improved upon, or is this already right?

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  • How does throwing an ArgumentNullException help?

    - by Scott Whitlock
    Let's say I have a method: public void DoSomething(ISomeInterface someObject) { if(someObject == null) throw new ArgumentNullException("someObject"); someObject.DoThisOrThat(); } I've been trained to believe that throwing the ArgumentNullException is "correct" but an "Object reference not set to an instance of an object" error means I have a bug. Why? I know that if I was caching the reference to someObject and using it later, then it's better to check for nullity when passed in, and fail early. However, if I'm dereferencing it on the next line, why are we supposed to do the check? It's going to throw an exception one way or the other. Edit: It just occurred to me... does the fear of the dereferenced null come from a language like C++ that doesn't check for you (i.e. it just tries to execute some method at memory location zero + method offset)?

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  • yield – Just yet another sexy c# keyword?

    - by George Mamaladze
    yield (see NSDN c# reference) operator came I guess with .NET 2.0 and I my feeling is that it’s not as wide used as it could (or should) be.   I am not going to talk here about necessarity and advantages of using iterator pattern when accessing custom sequences (just google it).   Let’s look at it from the clean code point of view. Let's see if it really helps us to keep our code understandable, reusable and testable.   Let’s say we want to iterate a tree and do something with it’s nodes, for instance calculate a sum of their values. So the most elegant way would be to build a recursive method performing a classic depth traversal returning the sum.           private int CalculateTreeSum(Node top)         {             int sumOfChildNodes = 0;             foreach (Node childNode in top.ChildNodes)             {                 sumOfChildNodes += CalculateTreeSum(childNode);             }             return top.Value + sumOfChildNodes;         }     “Do One Thing” Nevertheless it violates one of the most important rules “Do One Thing”. Our  method CalculateTreeSum does two things at the same time. It travels inside the tree and performs some computation – in this case calculates sum. Doing two things in one method is definitely a bad thing because of several reasons: ·          Understandability: Readability / refactoring ·          Reuseability: when overriding - no chance to override computation without copying iteration code and vice versa. ·          Testability: you are not able to test computation without constructing the tree and you are not able to test correctness of tree iteration.   I want to spend some more words on this last issue. How do you test the method CalculateTreeSum when it contains two in one: computation & iteration? The only chance is to construct a test tree and assert the result of the method call, in our case the sum against our expectation. And if the test fails you do not know wether was the computation algorithm wrong or was that the iteration? At the end to top it all off I tell you: according to Murphy’s Law the iteration will have a bug as well as the calculation. Both bugs in a combination will cause the sum to be accidentally exactly the same you expect and the test will PASS. J   Ok let’s use yield! That’s why it is generally a very good idea not to mix but isolate “things”. Ok let’s use yield!           private int CalculateTreeSumClean(Node top)         {             IEnumerable<Node> treeNodes = GetTreeNodes(top);             return CalculateSum(treeNodes);         }             private int CalculateSum(IEnumerable<Node> nodes)         {             int sumOfNodes = 0;             foreach (Node node in nodes)             {                 sumOfNodes += node.Value;             }             return sumOfNodes;         }           private IEnumerable<Node> GetTreeNodes(Node top)         {             yield return top;             foreach (Node childNode in top.ChildNodes)             {                 foreach (Node currentNode in GetTreeNodes(childNode))                 {                     yield return currentNode;                 }             }         }   Two methods does not know anything about each other. One contains calculation logic another jut the iteration logic. You can relpace the tree iteration algorithm from depth traversal to breath trevaersal or use stack or visitor pattern instead of recursion. This will not influence your calculation logic. And vice versa you can relace the sum with product or do whatever you want with node values, the calculateion algorithm is not aware of beeng working on some tree or graph.  How about not using yield? Now let’s ask the question – what if we do not have yield operator? The brief look at the generated code gives us an answer. The compiler generates a 150 lines long class to implement the iteration logic.       [CompilerGenerated]     private sealed class <GetTreeNodes>d__0 : IEnumerable<Node>, IEnumerable, IEnumerator<Node>, IEnumerator, IDisposable     {         ...        150 Lines of generated code        ...     }   Often we compromise code readability, cleanness, testability, etc. – to reduce number of classes, code lines, keystrokes and mouse clicks. This is the human nature - we are lazy. Knowing and using such a sexy construct like yield, allows us to be lazy, write very few lines of code and at the same time stay clean and do one thing in a method. That's why I generally welcome using staff like that.   Note: The above used recursive depth traversal algorithm is possibly the compact one but not the best one from the performance and memory utilization point of view. It was taken to emphasize on other primary aspects of this post.

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  • Understanding the Customer Form in Release 12 from an AR Perspective!!

    - by user793553
    Confused by the Customer Form in Release 12??  Read on, to get some insight into the evolution of this screen, and how it links in with Trading Community Architecture. Historically, the customer data model was owned by Oracle Receivables (AR).  However, as the data model changed and more complex relationships and attributes had to be tracked and monitored, the Trading Community Architecture (TCA) product was created.  All applications within the E-Business suite that require interaction with a customer integrate with TCA. Customer information is no longer stored in the individual applications but rather in a central repository/registry maintained within TCA.  It is important to understand the following entities/concepts stored in TCA: Party: A party is an entity with whom you can have a potential business relationship.  A party can be either a Person or an Organization.  The Party entity is completely independent of any business relationship; this means that a Party can exist even if you have no transactions with it.   The Party is the "umbrella" entity under which you capture all other attributes listed below. Customer: A customer is a party with whom you have an existing business relationship.  From an AR perspective, you can simplify the concepts by thinking of a Customer as a Party. This definition however does not apply to all other applications. In the Oracle Receivables Customer form, the information displayed at the Customer level is from TCA's Party information record. Customer Account (also called Account): An account contains information about how you transact business with a particular customer.  You can create multiple accounts for a customer.  When you create invoices and receipts you associate it to a particular Account of a Customer. Location: A Location is an address.  It is a point in space, typically identified by a street number, a street name, a city, a state or province, a country.  A location is independent of what it is used for - you do not associate a purpose to a location. Party Site: A Party Site is associated to a Party.  It is the location where a party is physically located.  When defining sites for a Party, only one can be an identifying address.  However, you can define other party sites associated to a party. You can define purposes/usage for Party Sites. Account Site: An Account Site is associated to a Customer Account. It is the location associated to the account you are transacting business with. You can define business purposes (also called site uses) for an Account site. Read more about the Customer Workbench in these notes: Doc ID 1436547.1 Oracle Receivables: Understanding the Customer Form in Release 12 Doc ID  1437866.1 Customer Form - Address: Troubleshooting, Known Issues and Patches Doc ID  1448442.1 Oracle Receivables (AR): Customer Workbench Information Center Do you find this type of blog entry useful?  Please add comments to let us know how we can help you more effectively.  Thank you!

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  • How are Java ByteBuffer's limit and position variable's updated?

    - by Dummy Derp
    There are two scenarios: writing and reading Writing: Whenever I write something to the ByteBuffer by calling its put(byte[]) method the position variable is incremented as: current position + size of byte[] and limit stays at the max. If, however, I put the data in a view buffer then I will have to, manually, calculate and update the position Before I call the write(ByteBuffer) method of the channel to write something, I will have to flip() the Bytebuffer so that position points to zero and limit points to the last byte that was written to the ByteBuffer. Reading: Whenever I call the read(ByteBuffer) method of a channel to read something, the position variable stays at 0 and the limit variable of the ByteBuffer points to the last byte that was read. So, if the ByteBuffer is smaller than the file being read, the limit variable is pushed to max This means that the ByteBuffer is already flipped and I can proceed to extracting the values from the ByteBuffer. Please, correct me where I am wrong :)

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  • What are good reasons to use explicit interface implementation for the sole purpose of hiding members?

    - by Nathanus
    During one of my studies into the intricacies of C#, I came across an interesting passage concerning explicit interface implementation. While this syntax is quite helpful when you need to resolve name clashes, you can use explicit interface implementation simply to hide more "advanced" members from the object level. The difference between allowing the use of object.method() or requiring the casting of ((Interface)object).method() seems like mean-spirited obfuscation to my inexperienced eyes. The text noted that this will hide the method from Intellisense at the object level, but why would you want to do that if it was not necessary to avoid name conflicts?

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  • Python response parse [migrated]

    - by Pavel Shevelyov
    When I'm sending some data on host: r = urllib2.Request(url, data = data, headers = headers) page = urllib2.urlopen(r) print page.read() I have something like this: [{"command":"settings","settings":{"basePath":"\/","ajaxPageState":{"theme":"spsr","theme_token":"kRHUhchUVpxAMYL8Y8IoyYIcX0cPrUstziAi8gSmMYk","css":[]},"ajax":{"edit-submit":{"callback":"spsr_calculator_form_ajax","wrapper":"calculator_form","method":"replaceWith","event":"mousedown","keypress":true,"url":"\/ru\/system\/ajax","submit":{"_triggering_element_name":"submit"}}}},"merge":true},{"command":"insert","method":null,"selector":null,"data":"\u003cdiv id=\"calculator_form\"\u003e\u003cform action=\"\/ru\/service\/calculator\" method=\"post\" id=\"spsr-calculator-form\" accept-charset=\"UTF-8\"\u003e\u003cdiv\u003e\u003cinput id=\"edit-from-ship-region-id\" type=\"hidden\" name=\"from_ship_region_id\" value=\"\" \/\u003e\n\u003cinput type=\"hidden\" name=\"form_build_id\" value=\"form-0RK_WFli4b2kUDTxpoqsGPp14B_0yf6Fz9x7UK-T3w8\" \/\u003e\n\u003cinput type=\"hidden\" name=\"form_id\" value=\"spsr_calculator_form\" \/\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"bg_p\"\u003e \n\u0421\u0435\u0439\u0447\u0430\u0441 \u0412\u044b... bla bla bla but I want have something, like this: <html><h1>bla bla bla</h1></html> How can I do it?

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  • Migrating Core Data to new UIManagedDocument in iOS 5

    - by samerpaul
    I have an app that has been on the store since iOS 3.1, so there is a large install base out there that still uses Core Data loaded up in my AppDelegate. In the most recent set of updates, I raised the minimum version to 4.3 but still kept the same way of loading the data. Recently, I decided it's time to make the minimum version 5.1 (especially with 6 around the corner), so I wanted to start using the new fancy UIManagedDocument way of using Core Data. The issue with this though is that the old database file is still sitting in the iOS app, so there is no migrating to the new document. You have to basically subclass UIManagedDocument with a new model class, and override a couple of methods to do it for you. Here's a tutorial on what I did for my app TimeTag.  Step One: Add a new class file in Xcode and subclass "UIManagedDocument" Go ahead and also add a method to get the managedObjectModel out of this class. It should look like:   @interface TimeTagModel : UIManagedDocument   - (NSManagedObjectModel *)managedObjectModel;   @end   Step two: Writing the methods in the implementation file (.m) I first added a shortcut method for the applicationsDocumentDirectory, which returns the URL of the app directory.  - (NSURL *)applicationDocumentsDirectory {     return [[[NSFileManagerdefaultManager] URLsForDirectory:NSDocumentDirectoryinDomains:NSUserDomainMask] lastObject]; }   The next step was to pull the managedObjectModel file itself (.momd file). In my project, it's called "minimalTime". - (NSManagedObjectModel *)managedObjectModel {     NSString *path = [[NSBundlemainBundle] pathForResource:@"minimalTime"ofType:@"momd"];     NSURL *momURL = [NSURL fileURLWithPath:path];     NSManagedObjectModel *managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:momURL];          return managedObjectModel; }   After that, I need to check for a legacy installation and migrate it to the new UIManagedDocument file instead. This is the overridden method: - (BOOL)configurePersistentStoreCoordinatorForURL:(NSURL *)storeURL ofType:(NSString *)fileType modelConfiguration:(NSString *)configuration storeOptions:(NSDictionary *)storeOptions error:(NSError **)error {     // If legacy store exists, copy it to the new location     NSURL *legacyPersistentStoreURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"minimalTime.sqlite"];          NSFileManager* fileManager = [NSFileManagerdefaultManager];     if ([fileManager fileExistsAtPath:legacyPersistentStoreURL.path])     {         NSLog(@"Old db exists");         NSError* thisError = nil;         [fileManager replaceItemAtURL:storeURL withItemAtURL:legacyPersistentStoreURL backupItemName:niloptions:NSFileManagerItemReplacementUsingNewMetadataOnlyresultingItemURL:nilerror:&thisError];     }          return [superconfigurePersistentStoreCoordinatorForURL:storeURL ofType:fileType modelConfiguration:configuration storeOptions:storeOptions error:error]; }   Basically what's happening above is that it checks for the minimalTime.sqlite file inside the app's bundle on the iOS device.  If the file exists, it tells you inside the console, and then tells the fileManager to replace the storeURL (inside the method parameter) with the legacy URL. This basically gives your app access to all the existing data the user has generated (otherwise they would load into a blank app, which would be disastrous). It returns a YES if successful (by calling it's [super] method). Final step: Actually load this database Due to how my app works, I actually have to load the database at launch (instead of shortly after, which would be ideal). I call a method called loadDatabase, which looks like this: -(void)loadDatabase {     static dispatch_once_t onceToken;          // Only do this once!     dispatch_once(&onceToken, ^{         // Get the URL         // The minimalTimeDB name is just something I call it         NSURL *url = [[selfapplicationDocumentsDirectory] URLByAppendingPathComponent:@"minimalTimeDB"];         // Init the TimeTagModel (our custom class we wrote above) with the URL         self.timeTagDB = [[TimeTagModel alloc] initWithFileURL:url];           // Setup the undo manager if it's nil         if (self.timeTagDB.undoManager == nil){             NSUndoManager *undoManager = [[NSUndoManager  alloc] init];             [self.timeTagDB setUndoManager:undoManager];         }                  // You have to actually check to see if it exists already (for some reason you can't just call "open it, and if it's not there, create it")         if ([[NSFileManagerdefaultManager] fileExistsAtPath:[url path]]) {             // If it does exist, try to open it, and if it doesn't open, let the user (or at least you) know!             [self.timeTagDB openWithCompletionHandler:^(BOOL success){                 if (!success) {                     // Handle the error.                     NSLog(@"Error opening up the database");                 }                 else{                     NSLog(@"Opened the file--it already existed");                     [self refreshData];                 }             }];         }         else {             // If it doesn't exist, you need to attempt to create it             [self.timeTagDBsaveToURL:url forSaveOperation:UIDocumentSaveForCreatingcompletionHandler:^(BOOL success){                 if (!success) {                     // Handle the error.                     NSLog(@"Error opening up the database");                 }                 else{                     NSLog(@"Created the file--it did not exist");                     [self refreshData];                 }             }];         }     }); }   If you're curious what refreshData looks like, it sends out a NSNotification that the database has been loaded: -(void)refreshData {     NSNotification* refreshNotification = [NSNotificationnotificationWithName:kNotificationCenterRefreshAllDatabaseData object:self.timeTagDB.managedObjectContext  userInfo:nil];     [[NSNotificationCenter defaultCenter] postNotification:refreshNotification];     }   The kNotificationCenterRefreshAllDatabaseData is just a constant I have defined elsewhere that keeps track of all the NSNotification names I use. I pass the managedObjectContext of the newly created file so that my view controllers can have access to it, and start passing it around to one another. The reason we do this as a Notification is because this is being run in the background, so we can't know exactly when it finishes. Make sure you design your app for this! Have some kind of loading indicator, or make sure your user can't attempt to create a record before the database actually exists, because it will crash the app.

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  • Is conditional return type ever a good idea?

    - by qegal
    So I have a method that's something like this: -(BOOL)isSingleValueRecord And another method like this: -(Type)typeOfSingleValueRecord And it occurred to me that I could combine them into something like this: -(id)isSingleValueRecord And have the implementation be something like this: -(id)isSingleValueRecord { //If it is single value if(self.recordValue = 0) { //Do some stuff to determine type, then return it return typeOfSingleValueRecord; } //If its not single value else { //Return "NO" return [NSNumber numberWithBool:NO]; } } So combining the two methods makes it more efficient but makes the readability go down. In my gut, I feel like I should go with the two-method version, but is that really right? Is there any case that I should go with the combined version?

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  • Commenting Code AS3 - Not being an API

    - by Marcelo Noronha
    How should I comment a method? What are the best practices on commenting code? Example: /* Checks if a color is allowed in a given point * of the bitmapdata of the current floor * @param value - color to be checked * @return boolean - if color is allowed returns true, else, return false */ private function isAllowed(value:uint):Boolean { //code... } Is that the best way to comment a method? I´ve heard there´s the use of the tag @see. What should be on this tag? I wonder if it could be something that has a relation to the method, is that right? Thanks.

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  • Deterministic Multiplayer RTS game questions?

    - by Martin K
    I am working on a cross-platform multiplayer RTS game where the different clients and a server(flash and C#), all need to stay deterministically synchronised. To deal with Floatpoint inconsistencies, I've come across this method: http://joshblog.net/2007/01/30/flash-floating-point-number-errors/#comment-49912 which basically truncates off the nondeterministic part: return Math.round(1000 * float) / 1000; Howewer my concern is that every time there is a division, there is further chance of creating additional floatpoint errors, in essence making it worse? . So it occured to me, how about something like this: function floatSafe(number:Number) : Number {return Math.round(float* 1024) / 1024; } ie dividing with only powers of 2 ? What do you think? . Ironically with the above method I got less accurate results: trace( floatSafe(3/5) ) // 0.599609375 where as with the other method(dividing with 1000), or just tracing the raw value I am getting 3/5 = 0.6 or Maybe thats what 3/5 actually is, IE 0.6 cannot really be represented with a floatpoint datatype, and would be more consistent across different platforms?

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  • Methodology for Documenting Existing Code Base

    - by George Stocker
    I work as part of a team on an existing application that has no inline documentation, nor does it have technical documentation. As I've been working on various bug reports on the application, I've written a sort of breadcrumb trail for myself - bug numbers in various places so that the next developer can refer to that bug number to see what was going on. My question is thus: What is the most effecient method for documenting this code? Should I document as I touch the area (the virus method, if you will), or should I document from each section on its own, and not follow paths that branch out into other areas of the application? Should I insert inline comments where none previously existed (with the fear that I may end up incorrectly identifying what the code does)? What method would you use to accurately and quickly document a rather large application that has no existing inline documentation, nor inline references to external documentation?

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  • Switching between levels, re-initialize existing structure or create new one?

    - by Martino Wullems
    This is something I've been wondering for quite a while. When building games that exist out of multiple levels (platformers, shmups etc) what is the prefered method to switch between the levels? Let's say we have a level class that does the following: Load data for the level design (tiles), enemies, graphics etc. Setup all these elements in their appriopate locations and display them Start physics and game logic I'm stuck between the following 2 methods: 1: Throw away everything in the level class and make a new one, we have to load an entirely new level anyway! 2: pause the game logic and physics, unload all currents assets, then re-initialize those components with the level data for the new level. They both have their pros and cons. Method 1 is alot easier and seems to make sense since we have to redo everything anyway. But method 2 allows you to re-use exisiting elements which might save resources and allows for a smoother transfer to the new level.

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  • RequestContextHolder.currentRequestAttributes() and accessing HTTP Session

    - by Umesh Awasthi
    Need to access HTTP session for fetching as well storing some information.I am using Spring-MVC for my application and i have 2 options here. User Request/ Session in my Controller method and do my work Use RequestContextHolde to access Session information. I am separating some calculation logic from Controller and want to access Session information in this new layer and for that i have 2 options Pass session or Request object to other method in other layer and perform my work. use RequestContextHolder.currentRequestAttributes() to access request/ session and perform my work. I am not sure which is right way to go? with second approach, i can see that method calling will be more clean and i need not to pass request/ session each time.

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  • Remove gravity from single body

    - by Siddharth
    I have multiple bodies in my game world in andengine. All the bodies affected by gravity but in that I want my specific body does not affected by the gravity. For that solution after research I found that I have to use body.setGravityScale(0) method for my problem solution. But in my andengine extension I don't found that method so please provide guidance about how get access about that method. Also for the above problem any other guidance will be acceptable. Thank You! I apply following code for reverse gravity final Vector2 vec = new Vector2(0, -SensorManager.GRAVITY_EARTH * bulletBody.getMass()); bulletBody.applyForce(vec, bulletBody.getWorldCenter());

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  • Resolving an App-Relative URL without a Page Object Reference

    - by Damon
    If you've worked with ASP.NET before then you've almost certainly seen an application-relative URL like ~/SomeFolder/SomePage.aspx.  The tilde at the beginning is a stand in for the application path, and it can easily be resolved using the Page object's ResolveUrl method: string url = Page.ResolveUrl("~/SomeFolder/SomePage.aspx"); There are times, however, when you don't have a page object available and you need to resolve an application relative URL.  Assuming you have an HttpContext object available, the following method will accomplish just that: public static string ResolveAppRelativeUrl(string url) {      return url.Replace("~", System.Web.HttpContext.Current.Request.ApplicationPath); } It just replaces the tilde with the application path, which is essentially all the ResolveUrl method does.

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  • What should I call the process of converting an object to a string?

    - by shabbychef
    We are having a game of 'semantic football' in the office over this matter: I am writing a method for an object which will represent the object as a string. That string should be such that when typed (more likely, cut and pasted) into the interpreter window (I will keep the language name out of this for now), will produce an object which is, for our purposes, identical to the one upon which the method was called. There is a spirited discussion over the 'best' name for this method. The terms pickle, serialize, deflate, etc have been proposed. However, it seems that those terms assume some process for the de-pickling (unserialization, etc) that is not necessarily the language interpreter itself. That is, they do not specifically refer to the case where strings of valid code are produced. This is closer to a quine, but we are re-producing the object not the code, so this is not quite right. any suggestions?

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  • Web Services Example - Part 2: Programmatic

    - by Denis T
    In this edition of the ADF Mobile blog we'll tackle part 2 of our Web Service examples.  In this posting we'll take a look at using a SOAP Web Service but calling it programmatically in code and parsing the return into a bean. Getting the sample code: Just click here to download a zip of the entire project.  You can unzip it and load it into JDeveloper and deploy it either to iOS or Android.  Please follow the previous blog posts if you need help getting JDeveloper or ADF Mobile installed.  Note: This is a different workspace than WS-Part1 Defining our Web Service: Just like our first installment, we are using the same public weather forecast web service provided free by CDYNE Corporation.  Sometimes this service goes down so please ensure you know it's up before reporting this example isn't working. We're going to concentrate on the same two web service methods, GetCityForecastByZIP and GetWeatherInformation. Defing the Application: The application setup is identical to the Weather1 version.  There are some improvements to the data that is displayed as part of this example though.  Now we are able to show the associated image along with each forecast line when using the Forecast By Zip feature.  We've also added the temperature Hi/Low values into the UI. Summary of Fundamental Changes In This Application The most fundamental change is that we're binding the UI to the Bean Data Controls instead of directly to the Web Service Data Controls.  This gives us much more flexibility to control the shape of the data and allows us to do caching of the data outside of the Web Service.  This way if your application is, say offline, your bean could still populate with data from a local cache and still show you some UI as opposed to completely failing because you don't have any connectivity. In general we promote this type of programming technique with ADF Mobile to insulate your application from any issues with network connectivity. What's different with this example? We have setup the Web Service DC the same way but now we have managed beans to process the data.  The following classes define the "Model" of our application:  CityInformation-CityForecast-Forecast, WeatherInformation-WeatherDescription.  We use WeatherBean for UI interaction to the model layer.  If you look through this example, we don't really do that much with the java code except use it to grab the image URL from the weather description.  In a more realistic example, you might be using some JDBC classes to persist the data to a local database. To have a good architecture it is always good to keep your model and UI layers separate.  This gets muddied if you start to use bindings on a page invoked from Java code and this java code starts to become your "model" layer.  Since bindings are page specific, your model layer starts to become entwined with your UI.  Not good!  To help with this, we've added some utility functions that let you invoke DC methods without having a binding and thus execute methods from your "model" layer without requiring a binding in your page definition.  We do this with the invokeDataControlMethod of the AdfmfJavaUtilities class.  An example of this method call is available in line 95 of WeatherInformation.java and line 93 of CityInformation.Java. What's a GenericType? Because Web Service Data Controls (and also URL Data Controls AKA REST) use generic name/value pairs to define their structure and don't have strongly typed objects, these are actually stored internally as GenericType objects.  The GenericType class is simply a property map of name/value pairs that can be hierarchical.  There are methods like getAttribute where you supply the index of the attribute or it's string property name.  Why is this important to know?  Because invokeDataControlMethod returns GenericType objects and developers either need to parse these GenericType objects themselves or use one of our helper functions. GenericTypeBeanSerializationHelper This class does exactly what it's name implies.  It's a helper class for developers to aid in serialization of GenericTypes to/from java objects.  This is extremely handy if you have a large GenericType object with many attributes (or you're just lazy like me!) and you just want to parse it out into a real java object you can use more easily.  Here you would use the fromGenericType method.  This method takes the class of the Java object you wish to return and the GenericType as parameters.  The method then parses through each attribute in the GenericType and uses reflection to set that same attribute in the Java class.  Then the method returns that new object of the class you specified.  This is obviously very handy to avoid a lot of shuffling code between GenericType and your own Java classes.  The reverse method, toGenericType is also available when you want to go the other way.  In this case you supply the string that represents the package location in the DataControl definition (Example: "MyDC.myParams.MyCollection") and then pass in the Java object you have that holds the data and a GenericType is returned to you.  Again, it will use reflection to calculate the attributes that match between the java class and the GenericType and call the getters/setters on those. Issues and Possible Improvements: In the next installment we'll show you how to make your web service calls asynchronously so your UI will fill dynamically when the service call returns but in the meantime you show the data you have locally in your bean fed from some local cache.  This gives your users instant delivery of some data while you fetch other data in the background.

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  • What's the equivalent name of "procedure" in OOP?

    - by AeroCross
    In several of my programming courses in the University, my teachers always told me the following: A function and a procedure are basically the same thing: the only difference is that a function returns a value, and the procedure doesn't. That means that this: function sum($a, $b) { return $a + $b; } ... is a function, and this: function sum($a, $b) { echo $a + $b; } ... is a procedure. In the same train of thought, I've seen that a method is the equivalent of a function in the OOP world. That means that this: class Example { function sum($a, $b) { return $a + $b; } } Is a method — but how do you call this? class Example { function sum($a, $b) { echo $a + $b; } } What's the equivalent name, or how do you call a method that doesn't returns anything?

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  • MAMP Pro Installed On Mavericks 10.9

    - by cnps
    I have MAMP Pro Installed. I'm well aware with the advanced features of MAMP Pro I can change to different types of Hosts, but I wanted to know why my previous method would not work within mavericks. This was my usual working method in 10.8, but now with 10.9 it's a headache. The previous method would: Write a custom address with the host address: "#Virtual Hosts" 127.0.0.1 nameofsite.local go to /Applications/MAMP/conf/apache and open the httpd.conf file, scroll to the bottom and then add NameVirtualHost * DocumentRoot "/Applications/MAMP/htdocs" ServerName localhost DocumentRoot "/Users/Klimt/Sites/siteoffolder" ServerName clientA.local make sure the ports is set to 80, 443, 3306. reset MAMP PRO and then usually type in the url address and it's gold from there. any help?

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