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  • Generic Data Structure Description Language

    - by Jon Purdy
    I am wondering whether there exists any declarative language for arbitrarily describing the format and semantics of a data structure, that can be compiled to a specific implementation of that structure in any of a set of target languages. That is, something like a generic data definition language but geared toward describing arbitrary data structures such as vectors, lists, trees, etc., and the semantics of operations on those structures. I ask because I had an idea for a feasible implementation of this concept, and I'm just wondering whether it's worth it, and, consequently, whether it's been done before. Another, slightly more abstract question: is there any real difference between the normative specification of a data structure (what it does) and its implementation (how it does it)?

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  • What's the best name for a non-mutating "add" method on an immutable collection?

    - by Jon Skeet
    Sorry for the waffly title - if I could come up with a concise title, I wouldn't have to ask the question. Suppose I have an immutable list type. It has an operation Foo(x) which returns a new immutable list with the specified argument as an extra element at the end. So to build up a list of strings with values "Hello", "immutable", "world" you could write: var empty = new ImmutableList<string>(); var list1 = empty.Foo("Hello"); var list2 = list1.Foo("immutable"); var list3 = list2.Foo("word"); (This is C# code, and I'm most interested in a C# suggestion if you feel the language is important. It's not fundamentally a language question, but the idioms of the language may be important.) The important thing is that the existing lists are not altered by Foo - so empty.Count would still return 0. Another (more idiomatic) way of getting to the end result would be: var list = new ImmutableList<string>().Foo("Hello"); .Foo("immutable"); .Foo("word"); My question is: what's the best name for Foo? EDIT 3: As I reveal later on, the name of the type might not actually be ImmutableList<T>, which makes the position clear. Imagine instead that it's TestSuite and that it's immutable because the whole of the framework it's a part of is immutable... (End of edit 3) Options I've come up with so far: Add: common in .NET, but implies mutation of the original list Cons: I believe this is the normal name in functional languages, but meaningless to those without experience in such languages Plus: my favourite so far, it doesn't imply mutation to me. Apparently this is also used in Haskell but with slightly different expectations (a Haskell programmer might expect it to add two lists together rather than adding a single value to the other list). With: consistent with some other immutable conventions, but doesn't have quite the same "additionness" to it IMO. And: not very descriptive. Operator overload for + : I really don't like this much; I generally think operators should only be applied to lower level types. I'm willing to be persuaded though! The criteria I'm using for choosing are: Gives the correct impression of the result of the method call (i.e. that it's the original list with an extra element) Makes it as clear as possible that it doesn't mutate the existing list Sounds reasonable when chained together as in the second example above Please ask for more details if I'm not making myself clear enough... EDIT 1: Here's my reasoning for preferring Plus to Add. Consider these two lines of code: list.Add(foo); list.Plus(foo); In my view (and this is a personal thing) the latter is clearly buggy - it's like writing "x + 5;" as a statement on its own. The first line looks like it's okay, until you remember that it's immutable. In fact, the way that the plus operator on its own doesn't mutate its operands is another reason why Plus is my favourite. Without the slight ickiness of operator overloading, it still gives the same connotations, which include (for me) not mutating the operands (or method target in this case). EDIT 2: Reasons for not liking Add. Various answers are effectively: "Go with Add. That's what DateTime does, and String has Replace methods etc which don't make the immutability obvious." I agree - there's precedence here. However, I've seen plenty of people call DateTime.Add or String.Replace and expect mutation. There are loads of newsgroup questions (and probably SO ones if I dig around) which are answered by "You're ignoring the return value of String.Replace; strings are immutable, a new string gets returned." Now, I should reveal a subtlety to the question - the type might not actually be an immutable list, but a different immutable type. In particular, I'm working on a benchmarking framework where you add tests to a suite, and that creates a new suite. It might be obvious that: var list = new ImmutableList<string>(); list.Add("foo"); isn't going to accomplish anything, but it becomes a lot murkier when you change it to: var suite = new TestSuite<string, int>(); suite.Add(x => x.Length); That looks like it should be okay. Whereas this, to me, makes the mistake clearer: var suite = new TestSuite<string, int>(); suite.Plus(x => x.Length); That's just begging to be: var suite = new TestSuite<string, int>().Plus(x => x.Length); Ideally, I would like my users not to have to be told that the test suite is immutable. I want them to fall into the pit of success. This may not be possible, but I'd like to try. I apologise for over-simplifying the original question by talking only about an immutable list type. Not all collections are quite as self-descriptive as ImmutableList<T> :)

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  • WordPress MU for hosting subdirectories

    - by Jon Lebensold
    Hi there, I'm trying to consolidate two WordPress installations into one WP MU install. Basically, I have example.com/blog and example.com/microsite/blog I'd like the microsite's blog and the /blog to both be hosted by WordPress MU. Does sunrise help me accomplish this? If not, how would I do this? Thanks!

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  • iPhone Simulator 3.x not supported after upgrading to XCode 3.2.3 Beta4 with OS 4.0

    - by Jon
    I've been having some problems, & since you guys are the smartest devs I thought I'd just ask you. When I last installed Xcode 3.2.3 Beta 2 (OS 4.0 support), it had all the iPhone Device & Simulator 3.x. Now, updated to Xcode 3.2.3 Beta 4 (OS 4.0 support), it no longer lists 3.x SDKs for either simulator or device in XCode. I'm aware that 3.2.3 changes the BASE SDK to 4.0, but how come none of the 3.x devices are available either? When I go to: /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs The only two files available are: iPhoneSimulator3.2.sdk iPhoneSimulator4.0.sdk However, when I go to: /Developer/Platforms/iPhoneOS.platform/DeviceSupport 3.0 3.0.1 3.1 3.1.1 3.1.2 3.1.3 3.2 4.0 (8A274b)

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  • .NET 4 SpinLock

    - by Jon Harrop
    The following test code (F#) is not returning the result I'd expect: let safeCount() = let n = 1000000 let counter = ref 0 let spinlock = ref <| SpinLock(false) let run i0 i1 () = for i=i0 to i1-1 do let locked = ref false try (!spinlock).Enter locked if !locked then counter := !counter + 1 finally if !locked then (!spinlock).Exit() let thread = System.Threading.Thread(run 0 (n/2)) thread.Start() run (n/2) n () thread.Join() !counter I'd expect the SpinLock to mutually exclude the counter and, therefore, for it to return counts of 1,000,000 but, instead, it returns smaller values as if no mutual exclusion is occurring. Any ideas what's wrong?

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  • Visual studio 2008/2010 dilemma

    - by jon
    We have a project which is being developed by a 3rd party. They are using LINQ and .NET 3.5 with Visual Studio 2008. We are currently at 2005 with .NET 2. Once they have delivered the code to us, we are unsure as to whether we will be able to compile/build their code using our current Visual Studio toolkit. I know we can download .NET 3.5, but unsure as to whether we will have problems with Visual Studio. So we are considering to upgrade. But since Visual Studio 2010 is soon to be released do we wait for that or upgrade to 2008?

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  • spike in my inverse fourier transform

    - by Jon
    I am trying to compare two data sets in MATLAB. To do this I need to filter the data sets by Fourier transforming the data, filtering it and then inverse Fourier transforming it. When I inverse Fourier transform the data however I get a spike at either end of the red data set (picture shows the first spike), it should be close to zero at the start, like the blue line. I am comparing many data sets and this only happens occasionally. I have three questions about this phenomenon. First, what may be causing it, secondly, how can I remedy it, and third, will it affect the data further along the time series or just at the beginning and end of the time series as it appears to from the picture. Any help would be great thanks.

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  • Proper way to copy a readonly NSMutableArray

    - by Jon Hull
    I have an object with a readonly property that I am trying to implement NSCopying for. It has a mutableArray called "subConditions" (which holds "SubCondition" objects). I have made it readonly because I want callers to be able to change the data in the array, but not the array itself. This worked really well until it was time to write the -copyWithZone: method. After fumbling around a bit, I managed to get something that seems to work. I am not sure if it is the best practice though. Here is a simplified version of my -copyWithZone: method: -(id)copyWithZone:(NSZone*)zone { Condition *copy = [[[self class]allocWithZone:zone]init]; NSArray *copiedArray = [[NSArray alloc]initWithArray:self.subConditions copyItems:YES]; [copy.subConditions setArray:copiedArray]; [copiedArray release]; return copy; } Is this the correct/best way to copy a readonly mutableArray?

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  • What's the strangest corner case you've seen in C# or .NET?

    - by Jon Skeet
    I collect a few corner cases and brain teasers and would always like to hear more. The page only really covers C# language bits and bobs, but I also find core .NET things interesting too. For example, here's one which isn't on the page, but which I find incredible: string x = new string(new char[0]); string y = new string(new char[0]); Console.WriteLine(object.ReferenceEquals(x, y)); I'd expect that to print False - after all, "new" (with a reference type) always creates a new object, doesn't it? The specs for both C# and the CLI indicate that it should. Well, not in this particular case. It prints True, and has done on every version of the framework I've tested it with. (I haven't tried it on Mono, admittedly...) Just to be clear, this is only an example of the kind of thing I'm looking for - I wasn't particularly looking for discussion/explanation of this oddity. (It's not the same as normal string interning; in particular, string interning doesn't normally happen when a constructor is called.) I was really asking for similar odd behaviour. Any other gems lurking out there?

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  • Best DNS Hosting?

    - by Jon Tackabury
    I am looking at setting up another dedicated hosting machine, and I would like to keep the DNS off of this box. When you host your projects do you just use the DNS provided by your name registrar/web host, or have you used an 3rd party DNS services? Who have you had good luck with?

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  • Uploadify refuses to upload WMV, FLV and MP4 files

    - by Jon Winstanley
    The uploadify plugin for JQuery seems very good and works for most file types. However, it allows me to upload all file types apart from the ones I need! Namely .WMV, .FLV and .MP4 I have googled the issue and not found anyonw having such difficulties. I have already tried changing the fileExt parameter and also tried removing it altogether. I have testing in Google Chrome, IE7 and Firefox and none work for thes efile types. Is there a known reason for this behaviour?

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  • Tell LINQ Distinct which item to return

    - by Jon
    I understand how to do a Distinct() on a IEnumerable and that I have to create an IEqualityComparer for more advanced stuff however is there a way in which you can tell which duplicated item to return? For example say you have a List<T> List<MyClass> test = new List<MyClass>(); test.Add(new MyClass {ID = 1, InnerID = 4}); test.Add(new MyClass {ID = 2, InnerID = 4}); test.Add(new MyClass {ID = 3, InnerID = 14}); test.Add(new MyClass {ID = 4, InnerID = 14}); You then do: var distinctItems = test.Distinct(new DistinctItemComparer()); class DistinctItemComparer : IEqualityComparer<MyClass> { public bool Equals(MyClass x, MyClass y) { return x.InnerID == y.InnerID;; } public int GetHashCode(MyClassobj) { return obj.InnerID.GetHasCode(); } } This code will return the classes with ID 1 and 3. Is there a way to return the ID matches 2 & 4.

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  • How do I escape a LIKE clause using NHibernate Criteria?

    - by Jon Seigel
    The code we're using is straight-forward in this part of the search query: myCriteria.Add( Expression.InsensitiveLike("Code", itemCode, MatchMode.Anywhere)); and this works fine in a production environment. The issue is that one of our clients has item codes that contain % symbols which this query needs to match. The resulting SQL output from this code is similar to: SELECT ... FROM ItemCodes WHERE ... AND Code LIKE '%ItemWith%Symbol%' which clearly explains why they're getting some odd results in item searches. Is there a way to enable escaping using the programmatic Criteria methods? Addendum: We're using a slightly old version of NHibernate, 2.1.0.4000 (current as of writing is 2.1.2.4853), but I checked the release notes, and there was no mention of a fix for this. I didn't find any open issue in their bugtracker either. We're using SQL Server, so I can escape the special characters (%, _, [, and ^) in code really easily, but the point of us using NHibernate was to make our application database-engine-independent as much as possible. Neither Restrictions.InsensitiveLike() nor HqlQueryUtil.GetLikeExpr() escape their inputs, and removing the MatchMode parameter makes no difference as far as escaping goes.

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  • Dev environment - Cubicles or pods?

    - by jon
    We're reorganizing our workspaces at work, and are individually being given the choice of working in a more open space with a few other developers, or a more closed off space by ourselves. Which should I choose?

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  • How do you exclude folders on get operation for sourcecontrol in CruiseControl.NET

    - by Jon
    I have a cruisecontrol.net project which currently doesn't monitor a source safe project. It is forced manually. Within the source control block however I want to be able to exclude the 'get' operation of a certain folder. I know there is a ExclusionFilter feature on a source control block in the config file, but I think that this excludes the sub folder from being monitored not from being retrieved from the repository. Can anyone confirm this is the case, or help me find out how I can achieve this? I'm using CCNet 1.4 and SourceSafe

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  • ByteStrings in Haskell

    - by Jon
    So i am trying to write a program that can read in a java class file as bytecode. For this i am using Data.Binary and Data.ByteStream. The problem i am having is because im pretty new to Haskell i am having trouble actually using these tools. module Main where import Data.Binary.Get import Data.Word import qualified Data.ByteString.Lazy as S getBinary :: Get Word8 getBinary = do a <- getWord8 return (a) main :: IO () main = do contents <- S.getContents print (getBinary contents) This is what i have come up with so far and i fear that its not really even on the right track. Although i know this question is very general i would appreciate some help with what i should be doing with the reading.

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  • Migrating From SQL Server Server 7 To 2005, What should I get excited about?

    - by Jon P
    The company I work for has decided to join the 21st century and upgrade our main database cluster from SQL Server 7 to SQL Server 2005. As a web developer what new whiz-bang features of SQL Server 2005 should I get excited about or get to know? Currently I'm mainly writing CRUD style queries, pretty much exclusively using Stored Procdures for a mixed ASP.net and Classic ASP environment.

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  • Implementing an async "read all currently available data from stream" operation

    - by Jon
    I recently provided an answer to this question: C# - Realtime console output redirection. As often happens, explaining stuff (here "stuff" was how I tackled a similar problem) leads you to greater understanding and/or, as is the case here, "oops" moments. I realized that my solution, as implemented, has a bug. The bug has little practical importance, but it has an extremely large importance to me as a developer: I can't rest easy knowing that my code has the potential to blow up. Squashing the bug is the purpose of this question. I apologize for the long intro, so let's get dirty. I wanted to build a class that allows me to receive input from a console's standard output Stream. Console output streams are of type FileStream; the implementation can cast to that, if needed. There is also an associated StreamReader already present to leverage. There is only one thing I need to implement in this class to achieve my desired functionality: an async "read all the data available this moment" operation. Reading to the end of the stream is not viable because the stream will not end unless the process closes the console output handle, and it will not do that because it is interactive and expecting input before continuing. I will be using that hypothetical async operation to implement event-based notification, which will be more convenient for my callers. The public interface of the class is this: public class ConsoleAutomator { public event EventHandler<ConsoleOutputReadEventArgs> StandardOutputRead; public void StartSendingEvents(); public void StopSendingEvents(); } StartSendingEvents and StopSendingEvents do what they advertise; for the purposes of this discussion, we can assume that events are always being sent without loss of generality. The class uses these two fields internally: protected readonly StringBuilder inputAccumulator = new StringBuilder(); protected readonly byte[] buffer = new byte[256]; The functionality of the class is implemented in the methods below. To get the ball rolling: public void StartSendingEvents(); { this.stopAutomation = false; this.BeginReadAsync(); } To read data out of the Stream without blocking, and also without requiring a carriage return char, BeginRead is called: protected void BeginReadAsync() { if (!this.stopAutomation) { this.StandardOutput.BaseStream.BeginRead( this.buffer, 0, this.buffer.Length, this.ReadHappened, null); } } The challenging part: BeginRead requires using a buffer. This means that when reading from the stream, it is possible that the bytes available to read ("incoming chunk") are larger than the buffer. Remember that the goal here is to read all of the chunk and call event subscribers exactly once for each chunk. To this end, if the buffer is full after EndRead, we don't send its contents to subscribers immediately but instead append them to a StringBuilder. The contents of the StringBuilder are only sent back whenever there is no more to read from the stream. private void ReadHappened(IAsyncResult asyncResult) { var bytesRead = this.StandardOutput.BaseStream.EndRead(asyncResult); if (bytesRead == 0) { this.OnAutomationStopped(); return; } var input = this.StandardOutput.CurrentEncoding.GetString( this.buffer, 0, bytesRead); this.inputAccumulator.Append(input); if (bytesRead < this.buffer.Length) { this.OnInputRead(); // only send back if we 're sure we got it all } this.BeginReadAsync(); // continue "looping" with BeginRead } After any read which is not enough to fill the buffer (in which case we know that there was no more data to be read during the last read operation), all accumulated data is sent to the subscribers: private void OnInputRead() { var handler = this.StandardOutputRead; if (handler == null) { return; } handler(this, new ConsoleOutputReadEventArgs(this.inputAccumulator.ToString())); this.inputAccumulator.Clear(); } (I know that as long as there are no subscribers the data gets accumulated forever. This is a deliberate decision). The good This scheme works almost perfectly: Async functionality without spawning any threads Very convenient to the calling code (just subscribe to an event) Never more than one event for each time data is available to be read Is almost agnostic to the buffer size The bad That last almost is a very big one. Consider what happens when there is an incoming chunk with length exactly equal to the size of the buffer. The chunk will be read and buffered, but the event will not be triggered. This will be followed up by a BeginRead that expects to find more data belonging to the current chunk in order to send it back all in one piece, but... there will be no more data in the stream. In fact, as long as data is put into the stream in chunks with length exactly equal to the buffer size, the data will be buffered and the event will never be triggered. This scenario may be highly unlikely to occur in practice, especially since we can pick any number for the buffer size, but the problem is there. Solution? Unfortunately, after checking the available methods on FileStream and StreamReader, I can't find anything which lets me peek into the stream while also allowing async methods to be used on it. One "solution" would be to have a thread wait on a ManualResetEvent after the "buffer filled" condition is detected. If the event is not signaled (by the async callback) in a small amount of time, then more data from the stream will not be forthcoming and the data accumulated so far should be sent to subscribers. However, this introduces the need for another thread, requires thread synchronization, and is plain inelegant. Specifying a timeout for BeginRead would also suffice (call back into my code every now and then so I can check if there's data to be sent back; most of the time there will not be anything to do, so I expect the performance hit to be negligible). But it looks like timeouts are not supported in FileStream. Since I imagine that async calls with timeouts are an option in bare Win32, another approach might be to PInvoke the hell out of the problem. But this is also undesirable as it will introduce complexity and simply be a pain to code. Is there an elegant way to get around the problem? Thanks for being patient enough to read all of this. Update: I definitely did not communicate the scenario well in my initial writeup. I have since revised the writeup quite a bit, but to be extra sure: The question is about how to implement an async "read all the data available this moment" operation. My apologies to the people who took the time to read and answer without me making my intent clear enough.

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