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• C++ function pointer as parameter

  - by Roland Soós

  Hello, I try to call a function which passed as function pointer with no argument, but I can't make it work. void *disconnectFunc; void D::setDisconnectFunc(void (*func)){ disconnectFunc = func; } void D::disconnected(){ *disconnectFunc; connected = false; }

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• Defining golang struct function using pointer or not

  - by Jacob

  Can someone explain to me why appending to an array works when you do this: func (s *Sample) Append(name string) { d := &Stuff{ name: name, } s.data = append(s.data, d) } Full code here But not when you do this: func (s Sample) Append(name string) { d := &Stuff{ name: name, } s.data = append(s.data, d) } Is there any reason at all why you would want to use the second example.

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• Error with python decorator

  - by Timmy

  I get this error object has no attribute 'im_func' with this class Test(object): def __init__(self, f): self.func = f def __call__( self, *args ): return self.func(*args) pylons code: class TestController(BaseController): @Test def index(self): return 'hello world'

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• C++: get const or non-const reference type from trait

  - by maciekp

  I am writing a functor F which takes function of type void (*func)(T) and func's argument arg. Then functor F calls func with arg. I would like F not to copy arg, just to pass it as reference. But then I cannot simply write "void F(void (*func)(T), T&)" because T could be a reference. So I am trying to write a trait, which allows to get proper reference type of T: T -> T& T& -> T& const T -> const T& const T& -> const T& I come up with something like this: template<typename T> struct type_op { typedef T& valid_ref_type; }; template<typename T> struct type_op<T&> { typedef typename type_op<T>::valid_ref_type valid_ref_type; }; template<typename T> struct type_op<const T> { typedef const T& valid_ref_type; }; template<typename T> struct type_op<const T&> { typedef const T& valid_ref_type; }; Which doesn't work for example for void a(int x) { std::cout << x << std::endl; } F(&a, 7); Giving error: invalid initialization of non-const reference of type ‘int&’ from a temporary of type ‘int’ in passing argument 2 of ‘void f(void (*)(T), typename type_op::valid_ref_type) [with T = int]’ How to get this trait to work?

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• Threads in C# [Question]

  - by blez

  Thread1/2: do TotalThreads-- on their exit int TotalThreads = 2; void AsyncFunc() { // run thread for Func() } void Func() { // run Thread1 // run Thread2 while(TotalThreads > 0) { /* do nothing */ } // some code } is that bad design?

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• AS3: How can I require a method argument to implement multiple interfaces?

  - by Anders

  The argument to my method func() must implement the two unrelated interfaces IFoo and IBar. Is there a better way of doing this than declaring another interface only for this purpose that inherits from IFoo and IBar and using that interface as the argument type? public interface IFooBar implements IFoo, IBar { } public function func(arg:IFooBar):void { } I'm developing for Flash Player 9.

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• Go - Return dynamically pointer to type

  - by nevalu

  Could dynamically be got a pointer to a type? type foo struct { A uint8 B string } func Testing() (*foo) {...} Using an interface? func Testing() (*interface{}) {...}

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• Directly Jump to another C++ function

  - by maligree

  I'm porting a small academic OS from TriCore to ARM Cortex (Thumb-2 instruction set). For the scheduler to work, I sometimes need to JUMP directly to another function without modifying the stack nor the link register. On TriCore (or, rather, on tricore-g++), this wrapper template (for any three-argument-function) works: template< class A1, class A2, class A3 > inline void __attribute__((always_inline)) JUMP3( void (*func)( A1, A2, A3), A1 a1, A2 a2, A3 a3 ) { typedef void (* __attribute__((interrupt_handler)) Jump3)( A1, A2, A3); ( (Jump3)func )( a1, a2, a3 ); } //example for using the template: JUMP3( superDispatch, this, me, next ); This would generate the assembler instruction J (a.k.a. JUMP) instead of CALL, leaving the stack and CSAs unchanged when jumping to the (otherwise normal) C++ function superDispatch(SchedulerImplementation* obj, Task::Id from, Task::Id to). Now I need an equivalent behaviour on ARM Cortex (or, rather, for arm-none-linux-gnueabi-g++), i.e. generate a B (a.k.a. BRANCH) instruction instead of BLX (a.k.a. BRANCH with link and exchange). But there is no interrupt_handler attribute for arm-g++ and I could not find any equivalent attribute. So I tried to resort to asm volatile and writing the asm code directly: template< class A1, class A2, class A3 > inline void __attribute__((always_inline)) JUMP3( void (*func)( A1, A2, A3), A1 a1, A2 a2, A3 a3 ) { asm volatile ( "mov.w r0, %1;" "mov.w r1, %2;" "mov.w r2, %3;" "b %0;" : : "r"(func), "r"(a1), "r"(a2), "r"(a3) : "r0", "r1", "r2" ); } So far, so good, in my theory, at least. Thumb-2 requires function arguments to be passed in the registers, i.e. r0..r2 in this case, so it should work. But then the linker dies with undefined reference to `r6' on the closing bracket of the asm statement ... and I don't know what to make of it. OK, I'm not the expert in C++, and the asm syntax is not very straightforward... so has anybody got a hint for me? A hint to the correct __attribute__ for arm-g++ would be one way, a hint to fix the asm code would be another. Another way maybe would be to tell the compiler that a1..a3 should already be in the registers r0..r2 when the asm statement is entered (I looked into that a bit, but did not find any hint).

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• Merge decorator function as class

  - by SyetemHog

  How to make this merge function as class decorator? def merge(*arg, **kwarg): # get decorator args & kwargs def func(f): def tmp(*args, **kwargs): # get function args & kwargs kwargs.update(kwarg) # merge two dictionaries return f(*args, **kwargs) # return merged data return tmp return func Usage: @other_decorator # return *args and **kwarg @merge(list=['one','two','three']) # need to merge with @other_decorator def test(*a, **k): # get merged args and kwargs print 'args:', a print 'kwargs:', k

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• PHP GD problem--not enough permission to make image?

  - by aaron

  Error: Warning: imagejpeg() [function.imagejpeg]: Unable to open 'images/xxx/xxx.jpg' for writing: Permission denied in /usr/www/users/xxx/resources/func.createthumbs.php on line 48 images/xxx/xxx/xxx.jpg Warning: Cannot modify header information - headers already sent by (output started at /usr/www/users/xxx/resources/updatethumbs.php:17) in /usr/www/users/xxx/resources/func.createthumbs.php on line 3 So... How can I change the permission? This is being run on a shared server--is it possible?

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• Why is the content of slice not changed in GO?

  - by Kid

  I thought that in GO language, slices are passed by reference. But why the following code doesn't change the content of slice c? Am I missing something? Thank you. package main import ( "fmt" ) func call(c []int) { c = append(c, 1) fmt.Println(c) } func main() { c := make([]int, 1, 5) fmt.Println(c) call(c) fmt.Println(c) } The result printed is: [0] [0 1] [0] while I was expecting [0] [0 1] [0 1]

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• How do I load a second view correctly in Swift?

  - by slooker

  I have a view that I'm trying to load in Swift like this, but it crashes with this error: 'NSInternalInconsistencyException', reason: '-[UIViewController _loadViewFromNibNamed:bundle:] loaded the "DetailView" nib but the view outlet was not set.' Here is the code I'm trying to use to load it. Second View Controller import UIKit class DetailViewController: UIViewController { @IBOutlet var nameField: UITextField override func viewDidLoad() { super.viewDidLoad() } } Code to load the view controller: var newViewController = DetailViewController() @IBAction func buttonTapped(AnyObject) { println("button tapped!") self.presentViewController(newViewController, animated: true, nil) } What am I doing wrong?

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• Getting length of ParellQuery collection

  - by dotnetdev

  Hi, Is there a way to get the length of a collection from this? ParallelQuery<string> Lines = File.ReadAllLines("Topics.txt").AsParallel<string>(); This has no length property. There is a count method but it takes a Func. If I don't pass a Func paremeter, I could get all the properties in the collection, but how could I not pass one in? Thanks

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• c++ Function pointer inlining

  - by wb

  I know I can pass a function pointer as a template parameter and get a call to it inlined but I wondered if any compilers these days can inline an 'obvious' inline-able function like: inline static void Print() { std::cout << "Hello\n"; } .... void (*func)() = Print; func(); Under Visual Studio 2008 its clever enough to get it down to a direct call instruction so it seems a shame it can't take it a step further?

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• How to pass array to function without variable instantiation, in C++

  - by Vincenzo

  Can I do this in C++ (if yes, what is the syntax?): void func(string* strs) { // do something } func({"abc", "cde"}); I want to pass an array to function, without instantiating it as a variable. Thanks for suggestions.

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• MapReduce in DryadLINQ and PLINQ

  - by JoshReuben

  MapReduce See http://en.wikipedia.org/wiki/Mapreduce The MapReduce pattern aims to handle large-scale computations across a cluster of servers, often involving massive amounts of data. "The computation takes a set of input key/value pairs, and produces a set of output key/value pairs. The developer expresses the computation as two Func delegates: Map and Reduce. Map - takes a single input pair and produces a set of intermediate key/value pairs. The MapReduce function groups results by key and passes them to the Reduce function. Reduce - accepts an intermediate key I and a set of values for that key. It merges together these values to form a possibly smaller set of values. Typically just zero or one output value is produced per Reduce invocation. The intermediate values are supplied to the user's Reduce function via an iterator." the canonical MapReduce example: counting word frequency in a text file.     MapReduce using DryadLINQ see http://research.microsoft.com/en-us/projects/dryadlinq/ and http://connect.microsoft.com/Dryad DryadLINQ provides a simple and straightforward way to implement MapReduce operations. This The implementation has two primary components: A Pair structure, which serves as a data container. A MapReduce method, which counts word frequency and returns the top five words. The Pair Structure - Pair has two properties: Word is a string that holds a word or key. Count is an int that holds the word count. The structure also overrides ToString to simplify printing the results. The following example shows the Pair implementation. public struct Pair { private string word; private int count; public Pair(string w, int c) { word = w; count = c; } public int Count { get { return count; } } public string Word { get { return word; } } public override string ToString() { return word + ":" + count.ToString(); } } The MapReduce function  that gets the results. the input data could be partitioned and distributed across the cluster. 1. Creates a DryadTable<LineRecord> object, inputTable, to represent the lines of input text. For partitioned data, use GetPartitionedTable<T> instead of GetTable<T> and pass the method a metadata file. 2. Applies the SelectMany operator to inputTable to transform the collection of lines into collection of words. The String.Split method converts the line into a collection of words. SelectMany concatenates the collections created by Split into a single IQueryable<string> collection named words, which represents all the words in the file. 3. Performs the Map part of the operation by applying GroupBy to the words object. The GroupBy operation groups elements with the same key, which is defined by the selector delegate. This creates a higher order collection, whose elements are groups. In this case, the delegate is an identity function, so the key is the word itself and the operation creates a groups collection that consists of groups of identical words. 4. Performs the Reduce part of the operation by applying Select to groups. This operation reduces the groups of words from Step 3 to an IQueryable<Pair> collection named counts that represents the unique words in the file and how many instances there are of each word. Each key value in groups represents a unique word, so Select creates one Pair object for each unique word. IGrouping.Count returns the number of items in the group, so each Pair object's Count member is set to the number of instances of the word. 5. Applies OrderByDescending to counts. This operation sorts the input collection in descending order of frequency and creates an ordered collection named ordered. 6. Applies Take to ordered to create an IQueryable<Pair> collection named top, which contains the 100 most common words in the input file, and their frequency. Test then uses the Pair object's ToString implementation to print the top one hundred words, and their frequency.   public static IQueryable<Pair> MapReduce( string directory, string fileName, int k) { DryadDataContext ddc = new DryadDataContext("file://" + directory); DryadTable<LineRecord> inputTable = ddc.GetTable<LineRecord>(fileName); IQueryable<string> words = inputTable.SelectMany(x => x.line.Split(' ')); IQueryable<IGrouping<string, string>> groups = words.GroupBy(x => x); IQueryable<Pair> counts = groups.Select(x => new Pair(x.Key, x.Count())); IQueryable<Pair> ordered = counts.OrderByDescending(x => x.Count); IQueryable<Pair> top = ordered.Take(k);   return top; }   To Test: IQueryable<Pair> results = MapReduce(@"c:\DryadData\input", "TestFile.txt", 100); foreach (Pair words in results) Debug.Print(words.ToString());   Note: DryadLINQ applications can use a more compact way to represent the query: return inputTable         .SelectMany(x => x.line.Split(' '))         .GroupBy(x => x)         .Select(x => new Pair(x.Key, x.Count()))         .OrderByDescending(x => x.Count)         .Take(k);     MapReduce using PLINQ The pattern is relevant even for a single multi-core machine, however. We can write our own PLINQ MapReduce in a few lines. the Map function takes a single input value and returns a set of mapped values àLINQ's SelectMany operator. These are then grouped according to an intermediate key à LINQ GroupBy operator. The Reduce function takes each intermediate key and a set of values for that key, and produces any number of outputs per key à LINQ SelectMany again. We can put all of this together to implement MapReduce in PLINQ that returns a ParallelQuery<T> public static ParallelQuery<TResult> MapReduce<TSource, TMapped, TKey, TResult>( this ParallelQuery<TSource> source, Func<TSource, IEnumerable<TMapped>> map, Func<TMapped, TKey> keySelector, Func<IGrouping<TKey, TMapped>, IEnumerable<TResult>> reduce) { return source .SelectMany(map) .GroupBy(keySelector) .SelectMany(reduce); } the map function takes in an input document and outputs all of the words in that document. The grouping phase groups all of the identical words together, such that the reduce phase can then count the words in each group and output a word/count pair for each grouping: var files = Directory.EnumerateFiles(dirPath, "*.txt").AsParallel(); var counts = files.MapReduce( path => File.ReadLines(path).SelectMany(line => line.Split(delimiters)), word => word, group => new[] { new KeyValuePair<string, int>(group.Key, group.Count()) });

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• Approaches for generic, compile-time safe lazy-load methods

  - by Aaronaught

  Suppose I have created a wrapper class like the following: public class Foo : IFoo { private readonly IFoo innerFoo; public Foo(IFoo innerFoo) { this.innerFoo = innerFoo; } public int? Bar { get; set; } public int? Baz { get; set; } } The idea here is that the innerFoo might wrap data-access methods or something similarly expensive, and I only want its GetBar and GetBaz methods to be invoked once. So I want to create another wrapper around it, which will save the values obtained on the first run. It's simple enough to do this, of course: int IFoo.GetBar() { if ((Bar == null) && (innerFoo != null)) Bar = innerFoo.GetBar(); return Bar ?? 0; } int IFoo.GetBaz() { if ((Baz == null) && (innerFoo != null)) Baz = innerFoo.GetBaz(); return Baz ?? 0; } But it gets pretty repetitive if I'm doing this with 10 different properties and 30 different wrappers. So I figured, hey, let's make this generic: T LazyLoad<T>(ref T prop, Func<IFoo, T> loader) { if ((prop == null) && (innerFoo != null)) prop = loader(innerFoo); return prop; } Which almost gets me where I want, but not quite, because you can't ref an auto-property (or any property at all). In other words, I can't write this: int IFoo.GetBar() { return LazyLoad(ref Bar, f => f.GetBar()); // <--- Won't compile } Instead, I'd have to change Bar to have an explicit backing field and write explicit getters and setters. Which is fine, except for the fact that I end up writing even more redundant code than I was writing in the first place. Then I considered the possibility of using expression trees: T LazyLoad<T>(Expression<Func<T>> propExpr, Func<IFoo, T> loader) { var memberExpression = propExpr.Body as MemberExpression; if (memberExpression != null) { // Use Reflection to inspect/set the property } } This plays nice with refactoring - it'll work great if I do this: return LazyLoad(f => f.Bar, f => f.GetBar()); But it's not actually safe, because someone less clever (i.e. myself in 3 days from now when I inevitably forget how this is implemented internally) could decide to write this instead: return LazyLoad(f => 3, f => f.GetBar()); Which is either going to crash or result in unexpected/undefined behaviour, depending on how defensively I write the LazyLoad method. So I don't really like this approach either, because it leads to the possibility of runtime errors which would have been prevented in the first attempt. It also relies on Reflection, which feels a little dirty here, even though this code is admittedly not performance-sensitive. Now I could also decide to go all-out and use DynamicProxy to do method interception and not have to write any code, and in fact I already do this in some applications. But this code is residing in a core library which many other assemblies depend on, and it seems horribly wrong to be introducing this kind of complexity at such a low level. Separating the interceptor-based implementation from the IFoo interface by putting it into its own assembly doesn't really help; the fact is that this very class is still going to be used all over the place, must be used, so this isn't one of those problems that could be trivially solved with a little DI magic. The last option I've already thought of would be to have a method like: T LazyLoad<T>(Func<T> getter, Action<T> setter, Func<IFoo, T> loader) { ... } This option is very "meh" as well - it avoids Reflection but is still error-prone, and it doesn't really reduce the repetition that much. It's almost as bad as having to write explicit getters and setters for each property. Maybe I'm just being incredibly nit-picky, but this application is still in its early stages, and it's going to grow substantially over time, and I really want to keep the code squeaky-clean. Bottom line: I'm at an impasse, looking for other ideas. Question: Is there any way to clean up the lazy-loading code at the top, such that the implementation will: Guarantee compile-time safety, like the ref version; Actually reduce the amount of code repetition, like the Expression version; and Not take on any significant additional dependencies? In other words, is there a way to do this just using regular C# language features and possibly a few small helper classes? Or am I just going to have to accept that there's a trade-off here and strike one of the above requirements from the list?

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• Performance of delegate and method group

  - by BlueFox

  Hi I was investigating the performance hit of creating Cachedependency objects, so I wrote a very simple test program as follows: using System; using System.Collections.Generic; using System.Diagnostics; using System.Web.Caching; namespace Test { internal class Program { private static readonly string[] keys = new[] {"Abc"}; private static readonly int MaxIteration = 10000000; private static void Main(string[] args) { Debug.Print("first set"); test7(); test6(); test5(); test4(); test3(); test2(); Debug.Print("second set"); test2(); test3(); test4(); test5(); test6(); test7(); } private static void test2() { DateTime start = DateTime.Now; var list = new List<CacheDependency>(); for (int i = 0; i < MaxIteration; i++) { list.Add(new CacheDependency(null, keys)); } Debug.Print("test2 Time: " + (DateTime.Now - start)); } private static void test3() { DateTime start = DateTime.Now; var list = new List<Func<CacheDependency>>(); for (int i = 0; i < MaxIteration; i++) { list.Add(() => new CacheDependency(null, keys)); } Debug.Print("test3 Time: " + (DateTime.Now - start)); } private static void test4() { var p = new Program(); DateTime start = DateTime.Now; var list = new List<Func<CacheDependency>>(); for (int i = 0; i < MaxIteration; i++) { list.Add(p.GetDep); } Debug.Print("test4 Time: " + (DateTime.Now - start)); } private static void test5() { var p = new Program(); DateTime start = DateTime.Now; var list = new List<Func<CacheDependency>>(); for (int i = 0; i < MaxIteration; i++) { list.Add(() => { return p.GetDep(); }); } Debug.Print("test5 Time: " + (DateTime.Now - start)); } private static void test6() { DateTime start = DateTime.Now; var list = new List<Func<CacheDependency>>(); for (int i = 0; i < MaxIteration; i++) { list.Add(GetDepSatic); } Debug.Print("test6 Time: " + (DateTime.Now - start)); } private static void test7() { DateTime start = DateTime.Now; var list = new List<Func<CacheDependency>>(); for (int i = 0; i < MaxIteration; i++) { list.Add(() => { return GetDepSatic(); }); } Debug.Print("test7 Time: " + (DateTime.Now - start)); } private CacheDependency GetDep() { return new CacheDependency(null, keys); } private static CacheDependency GetDepSatic() { return new CacheDependency(null, keys); } } } But I can't understand why these result looks like this: first set test7 Time: 00:00:00.4840277 test6 Time: 00:00:02.2041261 test5 Time: 00:00:00.1910109 test4 Time: 00:00:03.1401796 test3 Time: 00:00:00.1820105 test2 Time: 00:00:08.5394884 second set test2 Time: 00:00:07.7324423 test3 Time: 00:00:00.1830105 test4 Time: 00:00:02.3561347 test5 Time: 00:00:00.1750100 test6 Time: 00:00:03.2941884 test7 Time: 00:00:00.1850106 In particular: 1. Why is test4 and test6 much slower than their delegate version? I also noticed that Resharper specifically has a comment on the delegate version suggesting change test5 and test7 to "Covert to method group". Which is the same as test4 and test6 but they're actually slower? 2. I don't seem a consistent performance difference when calling test4 and test6, shouldn't static calls to be always faster?

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• Why does decorating a class break the descriptor protocol, thus preventing staticmethod objects from behaving as expected?

  - by Robru

  I need a little bit of help understanding the subtleties of the descriptor protocol in Python, as it relates specifically to the behavior of staticmethod objects. I'll start with a trivial example, and then iteratively expand it, examining it's behavior at each step: class Stub: @staticmethod def do_things(): """Call this like Stub.do_things(), with no arguments or instance.""" print "Doing things!" At this point, this behaves as expected, but what's going on here is a bit subtle: When you call Stub.do_things(), you are not invoking do_things directly. Instead, Stub.do_things refers to a staticmethod instance, which has wrapped the function we want up inside it's own descriptor protocol such that you are actually invoking staticmethod.__get__, which first returns the function that we want, and then gets called afterwards. >>> Stub <class __main__.Stub at 0x...> >>> Stub.do_things <function do_things at 0x...> >>> Stub.__dict__['do_things'] <staticmethod object at 0x...> >>> Stub.do_things() Doing things! So far so good. Next, I need to wrap the class in a decorator that will be used to customize class instantiation -- the decorator will determine whether to allow new instantiations or provide cached instances: def deco(cls): def factory(*args, **kwargs): # pretend there is some logic here determining # whether to make a new instance or not return cls(*args, **kwargs) return factory @deco class Stub: @staticmethod def do_things(): """Call this like Stub.do_things(), with no arguments or instance.""" print "Doing things!" Now, naturally this part as-is would be expected to break staticmethods, because the class is now hidden behind it's decorator, ie, Stub not a class at all, but an instance of factory that is able to produce instances of Stub when you call it. Indeed: >>> Stub <function factory at 0x...> >>> Stub.do_things Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'function' object has no attribute 'do_things' >>> Stub() <__main__.Stub instance at 0x...> >>> Stub().do_things <function do_things at 0x...> >>> Stub().do_things() Doing things! So far I understand what's happening here. My goal is to restore the ability for staticmethods to function as you would expect them to, even though the class is wrapped. As luck would have it, the Python stdlib includes something called functools, which provides some tools just for this purpose, ie, making functions behave more like other functions that they wrap. So I change my decorator to look like this: def deco(cls): @functools.wraps(cls) def factory(*args, **kwargs): # pretend there is some logic here determining # whether to make a new instance or not return cls(*args, **kwargs) return factory Now, things start to get interesting: >>> Stub <function Stub at 0x...> >>> Stub.do_things <staticmethod object at 0x...> >>> Stub.do_things() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'staticmethod' object is not callable >>> Stub() <__main__.Stub instance at 0x...> >>> Stub().do_things <function do_things at 0x...> >>> Stub().do_things() Doing things! Wait.... what? functools copies the staticmethod over to the wrapping function, but it's not callable? Why not? What did I miss here? I was playing around with this for a bit and I actually came up with my own reimplementation of staticmethod that allows it to function in this situation, but I don't really understand why it was necessary or if this is even the best solution to this problem. Here's the complete example: class staticmethod(object): """Make @staticmethods play nice with decorated classes.""" def __init__(self, func): self.func = func def __call__(self, *args, **kwargs): """Provide the expected behavior inside decorated classes.""" return self.func(*args, **kwargs) def __get__(self, obj, objtype=None): """Re-implement the standard behavior for undecorated classes.""" return self.func def deco(cls): @functools.wraps(cls) def factory(*args, **kwargs): # pretend there is some logic here determining # whether to make a new instance or not return cls(*args, **kwargs) return factory @deco class Stub: @staticmethod def do_things(): """Call this like Stub.do_things(), with no arguments or instance.""" print "Doing things!" Indeed it works exactly as expected: >>> Stub <function Stub at 0x...> >>> Stub.do_things <__main__.staticmethod object at 0x...> >>> Stub.do_things() Doing things! >>> Stub() <__main__.Stub instance at 0x...> >>> Stub().do_things <function do_things at 0x...> >>> Stub().do_things() Doing things! What approach would you take to make a staticmethod behave as expected inside a decorated class? Is this the best way? Why doesn't the builtin staticmethod implement __call__ on it's own in order for this to just work without any fuss? Thanks.

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• DOMDocument groupping nodes, with clone, nodeClone, importNode, fragment... What the better way?

  - by Peter Krauss

  A "DOMNodeList grouper" (groupList() function below) is a function that envelopes a set of nodes into a tag. Example: INPUT <root><b>10</b><a/><a>1</a><b>20</b><a>2</a></root> OUTPUT of groupList($dom->getElementsByTagName('a'),'G') <root><b>10</b> <G><a/><a>1</a><a>2</a></G> <b>20</b></root> There are many ways to implement it, what is the better? function groupList_v1(DOMNodeList &$list,$tag,&$dom) { $list = iterator_to_array($list); // to save itens $n = count($list); if ($n && $list[0]->nodeType==1) { $T = $dom->createDocumentFragment(); $T->appendChild($dom->createElement($tag)); for($i=0; $i<$n; $i++) { $T->firstChild->appendChild( clone $list[$i] ); if ($i) $list[$i]->parentNode->removeChild($list[$i]); } $dom->documentElement->replaceChild($T,$list[0]); }//if return $n; }//func function groupList_v2(DOMNodeList &$list,$tag,&$dom) { $list = iterator_to_array($list); // to save itens $n = count($list); if ($n && $list[0]->nodeType==1) { $T = $dom->createDocumentFragment(); $T->appendChild($dom->createElement($tag)); for($i=0; $i<$n; $i++) $T->firstChild->appendChild( clone $list[$i] ); $dom->documentElement->replaceChild($T,$list[0]); for($i=1; $i<$n; $i++) $list[$i]->parentNode->removeChild($list[$i]); }//if return $n; }//func // ... YOUR SUGGESTION ... // My ugliest function groupList_vN(DOMNodeList &$list,$tag,&$dom) { $list = iterator_to_array($list); // to save itens $n = count($list); if ($n && $list[0]->nodeType==1) { $d2 = new DOMDocument; $T = $d2->createElement($tag); for($i=0; $i<$n; $i++) $T->appendChild( $d2->importNode($list[$i], true) ); $dom->documentElement->replaceChild( $dom->importNode($T, true), $list[0] ); for($i=1; $i<$n; $i++) $list[$i]->parentNode->removeChild($list[$i]); }//if return $n; }//func Related questions: at stackoverflow, at codereview.

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• How to Process Lambda Expressions Passed as Argument Into Method - C# .NET 3.5

  - by Sunday Ironfoot

  My knowledge of Lambda expressions is a bit shaky, while I can write code that uses Lambda expressions (aka LINQ), I'm trying to write my own method that takes a few arguments that are of type Lambda Expression. Background: I'm trying to write a method that returns a Tree Collection of objects of type TreeItem from literally ANY other object type. I have the following so far: public class TreeItem { public string Id { get; set; } public string Text { get; set; } public TreeItem Parent { get; protected set; } public IList<TreeItem> Children { get { // Implementation that returns custom TreeItemCollection type } } public static IList<TreeItem> GetTreeFromObject<T>(IList<T> items, Expression<Func<T, string>> id, Expression<Func<T, string>> text, Expression<Func<T, IList<T>>> childProperty) where T : class { foreach (T item in items) { // Errrm!?? What do I do now? } return null; } } ...which can be called via... IList<TreeItem> treeItems = TreeItem.GetTreeFromObject<Category>( categories, c => c.Id, c => c.Name, c => c.ChildCategories); I could replace the Expressions with string values, and just use reflection, but I'm trying to avoid this as I want to make it strongly typed. My reasons for doing this is that I have a control that accepts a List of type TreeItem, whereas I have dozens of different types that are all in a tree like structure, and don't want to write seperate conversion methods for each type (trying to adhere to the DRY principle). Am I going about this the right way? Is there a better way of doing this perhaps?

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• Extra text shown on oveflow: hidden

  - by TRiG

  I'm keeping the main content area of the webpage small, so that footer navigation can be seen "above the fold". This is done by javascript setting the main content <div> thus: sec.style.height = '265px'; sec.style.overflow = 'hidden'; And then using javascript to insert a button to change the style back to normal: sec.style.height = 'auto'; The problem is that the cut-off point of 265px (dictated by the size of an image which I don't want to hide) doesn't quite match the gap between lines of text. This means that there the tops of tall letters show as funny little marks. Is there any way to hide text which is partially showing in a <div style="overflow: hidden;">? Edit to add: Full javascript var overflow = { hide: function() { var sec = app.get('content_section'); sec.style.height = '263px'; sec.style.overflow = 'hidden'; overflow.toggle(false); }, toggle: function(value) { var cnt = app.get('toggle_control'); if (value) { var func = 'hide'; cnt.innerHTML = 'Close « '; } else { var func = 'show'; cnt.innerHTML = 'More » '; } cnt.onclick = function() {eval('overflow.' + func + '();'); return false;}; cnt.style.cursor = 'pointer'; cnt.style.fontWeight = 'normal'; cnt.style.margin = '0 0 0 857px'; }, show: function() { var sec = app.get('content_section'); sec.style.height = 'auto'; overflow.toggle(true); } } if (document.addEventListener) { document.addEventListener('DOMContentLoaded', overflow.hide, false); } else { window.onload = function() {return overflow.hide();}; }

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• InvalidOperationException (Lambda parameter not in scope) when trying to Compile a Lambda Expression

  - by Moshe Levi

  Hello, I'm writing an Expression Parser to make my API more refactor friendly and less error prone. basicaly, I want the user to write code like that: repository.Get(entity => entity.Id == 10); instead of: repository.Get<Entity>("Id", 10); Extracting the member name from the left side of the binary expression was straight forward. The problems began when I tried to extract the value from the right side of the expression. The above snippet demonstrates the simplest possible case which involves a constant value but it can be much more complex involving closures and what not. After playing with that for some time I gave up on trying to cover all the possible cases myself and decided to use the framework to do all the heavy lifting for me by compiling and executing the right side of the expression. the relevant part of the code looks like that: public static KeyValuePair<string, object> Parse<T>(Expression<Func<T, bool>> expression) { var binaryExpression = (BinaryExpression)expression.Body; string memberName = ParseMemberName(binaryExpression.Left); object value = ParseValue(binaryExpression.Right); return new KeyValuePair<string, object>(memberName, value); } private static object ParseValue(Expression expression) { Expression conversionExpression = Expression.Convert(expression, typeof(object)); var lambdaExpression = Expression.Lambda<Func<object>>(conversionExpression); Func<object> accessor = lambdaExpression.Compile(); return accessor(); } Now, I get an InvalidOperationException (Lambda parameter not in scope) in the Compile line. when I googled for the solution I came up with similar questions that involved building an expression by hand and not supplying all the pieces, or trying to rely on parameters having the same name and not the same reference. I don't think that this is the case here because I'm reusing the given expression. I would appreciate if someone will give me some pointers on this. Thank you.

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• Mercurial fails while commiting/updating/etc. using Mercuriual+TrueCrypt+MAC

  - by lukewar

  While trying to work with Mercurial on project located on TrueCrypt partition I always get en error as follows: ** unknown exception encountered, details follow ** report bug details to http://mercurial.selenic.com/bts/ ** or [email protected] ** Mercurial Distributed SCM (version 1.5.2+20100502) ** Extensions loaded: Traceback (most recent call last): File "/usr/local/bin/hg", line 27, in mercurial.dispatch.run() File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 16, in run sys.exit(dispatch(sys.argv[1:])) File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 30, in dispatch return _runcatch(u, args) File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 50, in _runcatch return _dispatch(ui, args) File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 470, in _dispatch return runcommand(lui, repo, cmd, fullargs, ui, options, d) File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 340, in runcommand ret = _runcommand(ui, options, cmd, d) File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 521, in _runcommand return checkargs() File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 475, in checkargs return cmdfunc() File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 469, in d = lambda: util.checksignature(func)(ui, *args, **cmdoptions) File "/Library/Python/2.6/site-packages/mercurial/util.py", line 401, in check return func(*args, **kwargs) File "/Library/Python/2.6/site-packages/mercurial/commands.py", line 3332, in update return hg.update(repo, rev) File "/Library/Python/2.6/site-packages/mercurial/hg.py", line 362, in update stats = _merge.update(repo, node, False, False, None) File "/Library/Python/2.6/site-packages/mercurial/merge.py", line 495, in update _checkunknown(wc, p2) File "/Library/Python/2.6/site-packages/mercurial/merge.py", line 77, in _checkunknown for f in wctx.unknown(): File "/Library/Python/2.6/site-packages/mercurial/context.py", line 660, in unknown return self._status[4] File "/Library/Python/2.6/site-packages/mercurial/util.py", line 156, in get result = self.func(obj) File "/Library/Python/2.6/site-packages/mercurial/context.py", line 622, in _status return self._repo.status(unknown=True) File "/Library/Python/2.6/site-packages/mercurial/localrepo.py", line 1023, in status if (f not in ctx1 or ctx2.flags(f) != ctx1.flags(f) File "/Library/Python/2.6/site-packages/mercurial/context.py", line 694, in flags flag = findflag(self._parents[0]) File "/Library/Python/2.6/site-packages/mercurial/context.py", line 690, in findflag return ff(path) File "/Library/Python/2.6/site-packages/mercurial/dirstate.py", line 145, in f if 'x' in fallback(x): TypeError: argument of type 'NoneType' is not iterable It is worth mention that Mercurial works perfectly if project is not located on TrueCrypt partition. Configuration: MacOS X 10.6.3 Mercurial Distributed SCM (version 1.5.2+20100502) Python 2.6.5 Have anyone of you generous people able to help me? :)

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• Google's 'go' and scope/functions

  - by danwoods

  In one of the example servers given at golang.org: package main import ( "flag" "http" "io" "log" "template" ) var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18 var fmap = template.FormatterMap{ "html": template.HTMLFormatter, "url+html": UrlHtmlFormatter, } var templ = template.MustParse(templateStr, fmap) func main() { flag.Parse() http.Handle("/", http.HandlerFunc(QR)) err := http.ListenAndServe(*addr, nil) if err != nil { log.Exit("ListenAndServe:", err) } } func QR(c *http.Conn, req *http.Request) { templ.Execute(req.FormValue("s"), c) } func UrlHtmlFormatter(w io.Writer, v interface{}, fmt string) { template.HTMLEscape(w, []byte(http.URLEscape(v.(string)))) } const templateStr = ` <html> <head> <title>QR Link Generator</title> </head> <body> {.section @} <img src="http://chart.apis.google.com/chart?chs=300x300&cht=qr&choe=UTF- 8&chl={@|url+html}" /> <br> {@|html} <br> <br> {.end} <form action="/" name=f method="GET"><input maxLength=1024 size=70 name=s value="" title="Text to QR Encode"><input type=submit value="Show QR" name=qr> </form> </body> </html> ` Why is template.HTMLEscape(w, []byte(http.URLEscape(v.(string)))) contained within UrlHtmlFormatter? Why can't it be directly linked to "url+html"?

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