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  • Alter a function as a parameter before evaluating it?

    - by Shane
    Is there any way, given a function passed as a parameter, to alter its input parameter string before evaluating it? Here's pseudo-code for what I'm hoping to achieve: test.func <- function(a, b) { # here I want to alter the b expression before evaluating it: b(..., val1=a) } Given the function call passed to b, I want to add in a as another parameter without needing to always specify ... in the b call. So the output from this test.func call should be: test.func(a="a", b=paste(1, 2)) "1" "2" "a"

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  • how free of memory happen in this case???

    - by Riyaz
    #include <stdio.h> void func(int arr[],int xNumOfElem) { int j; for(j=0; j<xNumOfElem; j++) { arr[j] = j + arr[j]; printf("%d\t",arr[j]); } printf("\n"); } int main() { int *a,k; a = (int*) malloc(sizeof(int)*10); for(k = 0; k<10; k++) { a[k] = k; printf("%d\t",a[k]); } printf("\n"); func(a,10); //Func call free(a); } Inside the the function "func" who will allocate/deallocate memory for dynamic array "arr". arr is an function argument.

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  • Templates, Function Pointers and C++0x

    - by user328543
    One of my personal experiments to understand some of the C++0x features: I'm trying to pass a function pointer to a template function to execute. Eventually the execution is supposed to happen in a different thread. But with all the different types of functions, I can't get the templates to work. #include `<functional`> int foo(void) {return 2;} class bar { public: int operator() (void) {return 4;}; int something(int a) {return a;}; }; template <class C> int func(C&& c) { //typedef typename std::result_of< C() >::type result_type; typedef typename std::conditional< std::is_pointer< C >::value, std::result_of< C() >::type, std::conditional< std::is_object< C >::value, std::result_of< typename C::operator() >::type, void> >::type result_type; result_type result = c(); return result; } int main(int argc, char* argv[]) { // call with a function pointer func(foo); // call with a member function bar b; func(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); // call with a lambda expression func( [](void)->int {return 12;} ); return 0; } The result_of template alone doesn't seem to be able to find the operator() in class bar and the clunky conditional I created doesn't compile. Any ideas? Will I have additional problems with const functions?

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  • decorating a function and adding functionalities preserving the number of argument

    - by pygabriel
    I'd like to decorate a function, using a pattern like this: def deco(func): def wrap(*a,**kw): print "do something" return func(*a,**kw) return wrap The problem is that if the function decorated has a prototype like that: def function(a,b,c): return When decorated, the prototype is destroyed by the varargs, for example, calling function(1,2,3,4) wouldn't result in an exception. Is that a way to avoid that? How can define the wrap function with the same prototype as the decorated (func) one? There's something conceptually wrong?

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  • Go - Raise an exception

    - by nevalu
    I would want to raise an exception as it's made in Python or Java --to finish the program with an error message--. An error message could be returned to a parent function: func readFile(filename string) (content string, err os.Error) { content, err := ioutil.ReadFile(filename) if err != nil { return "", os.ErrorString("read " + filename + ": " + err) } return string(content), nil } but I want that it can be finished when the error is found. Would be correct the next one? func readFile(filename string) (content string) { content, err := ioutil.ReadFile(filename) defer func() { if err != nil { panic(err) } }() return string(content) }

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  • Castle Windsor Weak Typed Factory

    - by JeffN825
    In a very very limited number of scenarios, I need to go from an unknown Type (at compile time) to an instance of the object registered for that type. For the most part, I use typed factories and I know the type I want to resolve at compile time...so I inject a Func<IMyType> into a constructor ...but in these limited number of scenarios, in order to avoid a direct call to the container (and thus having to reference Windsor from the library, which is an anti-pattern I'd like to avoid), I need to inject a Func<Type,object>...which I want to internally container.Resolve(type) for the Type parameter of the Func. Does anyone have some suggestions on the easiest/most straightforward way of setting this up? I tried the following, but with this setup, I end up bypassing the regular TypedFactoryFacility altogether which is definitely not what I want: Kernel.Register(Component.For(typeof (Func<Type, object>)).LifeStyle.Singleton.UsingFactoryMethod( (kernel, componentModel, creationContext) => kernel.Resolve(/* not sure what to put here... */))); Thanks in advance for any assistance.

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  • Are vector assignments copied by value or by reference in Google's Go language?

    - by Brian T Hannan
    In the following code, I create one peg puzzle then do a move on it which adds a move to its movesAlreadyDone vector. Then I create another peg puzzle then do a move on it which adds a move to its movesAlreadyDone vector. When I print out the values in that vector for the second one, it has the move in it from the first one along with the move from the second one. Can anyone tell me why it seems to be assigning by reference and not value? Are vector assignments copied by value or by reference in Google's Go language? package main import "fmt" import "container/vector" type Move struct { x0, y0, x1, y1 int } type PegPuzzle struct { movesAlreadyDone * vector.Vector; } func (p *PegPuzzle) InitPegPuzzle(){ p.movesAlreadyDone = vector.New(0); } func NewChildPegPuzzle(parent *PegPuzzle) *PegPuzzle{ retVal := new(PegPuzzle); retVal.movesAlreadyDone = parent.movesAlreadyDone; return retVal } func (p *PegPuzzle) doMove(move Move){ p.movesAlreadyDone.Push(move); } func (p *PegPuzzle) printPuzzleInfo(){ fmt.Printf("-----------START----------------------\n"); fmt.Printf("moves already done: %v\n", p.movesAlreadyDone); fmt.Printf("------------END-----------------------\n"); } func main() { p := new(PegPuzzle); cp1 := new(PegPuzzle); cp2 := new(PegPuzzle); p.InitPegPuzzle(); cp1 = NewChildPegPuzzle(p); cp1.doMove(Move{1,1,2,3}); cp1.printPuzzleInfo(); cp2 = NewChildPegPuzzle(p); cp2.doMove(Move{3,2,5,1}); cp2.printPuzzleInfo(); } Any help will be greatly appreciated. Thanks!

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  • boost::function function pointer to parameters?

    - by high6
    How does boost::function take a function pointer and get parameters from it? I want wrap a function pointer so that it can be validated before being called. And it would be nice to be able to call it like boost::function is with the () operator and not having to access the function pointer member. Wrapper func; func(5); //Yes :D func.Ptr(5) //Easy to do, but not as nice looking

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  • Memory Management with returning char* function

    - by RageD
    Hello all, Today, without much thought, I wrote a simple function return to a char* based on a switch statement of given enum values. This, however, made me wonder how I could release that memory. What I did was something like this: char* func() { char* retval = new char; // Switch blah blah - will always return some value other than NULL since default: return retval; } I apologize if this is a naive question, but what is the best way to release the memory seeing as I cannot delete the memory after the return and, obviously, if I delete it before, I won't have a returned value. What I was thinking as a viable solution was something like this void func(char*& in) { // blah blah switch make it do something } int main() { char* val = new char; func(val); // Do whatever with func (normally func within a data structure with specific enum set so could run multiple times to change output) val = NULL; delete val; val = NULL; return 0; } Would anyone have anymore insight on this and/or explanation on which to use? Regards, Dennis M.

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  • What are the drawbacks of this Classing format?

    - by Keysle
    This is a 3 layer example of my classing format function __(_){return _.constructor} //class var _ = ( CLASS = function(){ this.variable = 0; this.sub = new CLASS.SUBCLASS(); }).prototype; _.func = function(){ alert('lvl'+this.variable); this.sub.func(); } _.divePeak = function(){ alert('lvl'+this.variable); this.sub.variable += 5; } //sub class _ = ( __(_).SUBCLASS = function(){ this.variable = 1; this.sub = new CLASS.SUBCLASS.DEEPCLASS(); }).prototype; _.func = function(){ alert('lvl'+this.variable); this.sub.func(); } //deep class _ = ( __(_).DEEPCLASS = function(){ this.variable = 2; }).prototype; _.func = function(){ alert('lvl'+this.variable); } Before you blow a gasket, let me explain myself. The purpose behind the underscores is to accelerate the time needed to specify functions for a class and also specify sub classes of a class. To me it's easier to read. I KNOW, this does interfere with underscore.js if you intend to use it in your classes. I'm sure _.js can be easily switched over to another $ymbol though ... oh wait, But I digress. Why have classes within a class? because solar.system() and social.system() mean two totally different things but it's convenient to use the same name. Why user underscores to manage the definition of the class? because "Solar.System.prototype" took me about 2 seconds to type out and 2 typos to correct. It also keeps all function names for all classes in the same column of texts, which is nice for legibility. All I'm doing is presenting my reasoning behind this method and why I came up with it. I'm 3 days into learning OO JS and I am very willing to accept that I might have messed up.

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  • Adding a method to a function object at runtime

    - by Carson Myers
    I read a question earlier asking if there was a times method in Python, that would allow a function to be called n times in a row. Everyone suggested for _ in range(n): foo() but I wanted to try and code a different solution using a function decorator. Here's what I have: def times(self, n, *args, **kwargs): for _ in range(n): self.__call__(*args, **kwargs) import new def repeatable(func): func.times = new.instancemethod(times, func, func.__class__) @repeatable def threeArgs(one, two, three): print one, two, three threeArgs.times(7, "one", two="rawr", three="foo") When I run the program, I get the following exception: Traceback (most recent call last): File "", line 244, in run_nodebug File "C:\py\repeatable.py", line 24, in threeArgs.times(7, "one", two="rawr", three="foo") AttributeError: 'NoneType' object has no attribute 'times' So I suppose the decorator didn't work? How can I fix this?

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  • command line arg?

    - by kaushik
    This is a module named XYZ. def func(x) ..... ..... if __name__=="__main__": print func(sys.argv[1]) Now I have imported this module in another code and want to use the func. How can i use it? import XYZ After this, where to give the argument, and syntax on how to call it, please?

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  • Detect if class has overloaded function fails on Comeau compiler

    - by Frank
    Hi Everyone, I'm trying to use SFINAE to detect if a class has an overloaded member function that takes a certain type. The code I have seems to work correctly in Visual Studio and GCC, but does not compile using the Comeau online compiler. Here is the code I'm using: #include <stdio.h> //Comeau doesnt' have boost, so define our own enable_if_c template<bool value> struct enable_if_c { typedef void type; }; template<> struct enable_if_c< false > {}; //Class that has the overloaded member function class TestClass { public: void Func(float value) { printf( "%f\n", value ); } void Func(int value) { printf( "%i\n", value ); } }; //Struct to detect if TestClass has an overloaded member function for type T template<typename T> struct HasFunc { template<typename U, void (TestClass::*)( U )> struct SFINAE {}; template<typename U> static char Test(SFINAE<U, &TestClass::Func>*); template<typename U> static int Test(...); static const bool Has = sizeof(Test<T>(0)) == sizeof(char); }; //Use enable_if_c to only allow the function call if TestClass has a valid overload for T template<typename T> typename enable_if_c<HasFunc<T>::Has>::type CallFunc(TestClass &test, T value) { test.Func( value ); } int main() { float value1 = 0.0f; int value2 = 0; TestClass testClass; CallFunc( testClass, value1 ); //Should call TestClass::Func( float ) CallFunc( testClass, value2 ); //Should call TestClass::Func( int ) } The error message is: no instance of function template "CallFunc" matches the argument list. It seems that HasFunc::Has is false for int and float when it should be true. Is this a bug in the Comeau compiler? Am I doing something that's not standard? And if so, what do I need to do to fix it?

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  • F#, Shadowing and Nested function

    - by Lian
    Hi! Here I want to understand how the mechanism of Shadowing and Nested function work. For example: let func y = let dup y = y + y let z = dup y let dup y = let dup z = let y = y * z y let z = y y dup z + z;; val func : int -> int > func 3;; val it : int = 12 Can someone explain what happen here?

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  • Implementing a generic repository for WCF data services

    - by cibrax
    The repository implementation I am going to discuss here is not exactly what someone would call repository in terms of DDD, but it is an abstraction layer that becomes handy at the moment of unit testing the code around this repository. In other words, you can easily create a mock to replace the real repository implementation. The WCF Data Services update for .NET 3.5 introduced a nice feature to support two way data bindings, which is very helpful for developing WPF or Silverlight based application but also for implementing the repository I am going to talk about. As part of this feature, the WCF Data Services Client library introduced a new collection DataServiceCollection<T> that implements INotifyPropertyChanged to notify the data context (DataServiceContext) about any change in the association links. This means that it is not longer necessary to manually set or remove the links in the data context when an item is added or removed from a collection. Before having this new collection, you basically used the following code to add a new item to a collection. Order order = new Order {   Name = "Foo" }; OrderItem item = new OrderItem {   Name = "bar",   UnitPrice = 10,   Qty = 1 }; var context = new OrderContext(); context.AddToOrders(order); context.AddToOrderItems(item); context.SetLink(item, "Order", order); context.SaveChanges(); Now, thanks to this new collection, everything is much simpler and similar to what you have in other ORMs like Entity Framework or L2S. Order order = new Order {   Name = "Foo" }; OrderItem item = new OrderItem {   Name = "bar",   UnitPrice = 10,   Qty = 1 }; order.Items.Add(item); var context = new OrderContext(); context.AddToOrders(order); context.SaveChanges(); In order to use this new feature, you first need to enable V2 in the data service, and then use some specific arguments in the datasvcutil tool (You can find more information about this new feature and how to use it in this post). DataSvcUtil /uri:"http://localhost:3655/MyDataService.svc/" /out:Reference.cs /dataservicecollection /version:2.0 Once you use those two arguments, the generated proxy classes will use DataServiceCollection<T> rather than a simple ObjectCollection<T>, which was the default collection in V1. There are some aspects that you need to know to use this feature correctly. 1. All the entities retrieved directly from the data context with a query track the changes and report those to the data context automatically. 2. A entity created with “new” does not track any change in the properties or associations. In order to enable change tracking in this entity, you need to do the following trick. public Order CreateOrder() {   var collection = new DataServiceCollection<Order>(this.context);   var order = new Order();   collection.Add(order);   return order; } You basically need to create a collection, and add the entity to that collection with the “Add” method to enable change tracking on that entity. 3. If you need to attach an existing entity (For example, if you created the entity with the “new” operator rather than retrieving it from the data context with a query) to a data context for tracking changes, you can use the “Load” method in the DataServiceCollection. var order = new Order {   Id = 1 }; var collection = new DataServiceCollection<Order>(this.context); collection.Load(order); In this case, the order with Id = 1 must exist on the data source exposed by the Data service. Otherwise, you will get an error because the entity did not exist. These cool extensions methods discussed by Stuart Leeks in this post to replace all the magic strings in the “Expand” operation with Expression Trees represent another feature I am going to use to implement this generic repository. Thanks to these extension methods, you could replace the following query with magic strings by a piece of code that only uses expressions. Magic strings, var customers = dataContext.Customers .Expand("Orders")         .Expand("Orders/Items") Expressions, var customers = dataContext.Customers .Expand(c => c.Orders.SubExpand(o => o.Items)) That query basically returns all the customers with their orders and order items. Ok, now that we have the automatic change tracking support and the expression support for explicitly loading entity associations, we are ready to create the repository. The interface for this repository looks like this,public interface IRepository { T Create<T>() where T : new(); void Update<T>(T entity); void Delete<T>(T entity); IQueryable<T> RetrieveAll<T>(params Expression<Func<T, object>>[] eagerProperties); IQueryable<T> Retrieve<T>(Expression<Func<T, bool>> predicate, params Expression<Func<T, object>>[] eagerProperties); void Attach<T>(T entity); void SaveChanges(); } The Retrieve and RetrieveAll methods are used to execute queries against the data service context. While both methods receive an array of expressions to load associations explicitly, only the Retrieve method receives a predicate representing the “where” clause. The following code represents the final implementation of this repository.public class DataServiceRepository: IRepository { ResourceRepositoryContext context; public DataServiceRepository() : this (new DataServiceContext()) { } public DataServiceRepository(DataServiceContext context) { this.context = context; } private static string ResolveEntitySet(Type type) { var entitySetAttribute = (EntitySetAttribute)type.GetCustomAttributes(typeof(EntitySetAttribute), true).FirstOrDefault(); if (entitySetAttribute != null) return entitySetAttribute.EntitySet; return null; } public T Create<T>() where T : new() { var collection = new DataServiceCollection<T>(this.context); var entity = new T(); collection.Add(entity); return entity; } public void Update<T>(T entity) { this.context.UpdateObject(entity); } public void Delete<T>(T entity) { this.context.DeleteObject(entity); } public void Attach<T>(T entity) { var collection = new DataServiceCollection<T>(this.context); collection.Load(entity); } public IQueryable<T> Retrieve<T>(Expression<Func<T, bool>> predicate, params Expression<Func<T, object>>[] eagerProperties) { var entitySet = ResolveEntitySet(typeof(T)); var query = context.CreateQuery<T>(entitySet); foreach (var e in eagerProperties) { query = query.Expand(e); } return query.Where(predicate); } public IQueryable<T> RetrieveAll<T>(params Expression<Func<T, object>>[] eagerProperties) { var entitySet = ResolveEntitySet(typeof(T)); var query = context.CreateQuery<T>(entitySet); foreach (var e in eagerProperties) { query = query.Expand(e); } return query; } public void SaveChanges() { this.context.SaveChanges(SaveChangesOptions.Batch); } } For instance, you can use the following code to retrieve customers with First name equal to “John”, and all their orders in a single call. repository.Retrieve<Customer>(    c => c.FirstName == “John”, //Where    c => c.Orders.SubExpand(o => o.Items)); In case, you want to have some pre-defined queries that you are going to use across several places, you can put them in an specific class. public static class CustomerQueries {   public static Expression<Func<Customer, bool>> LastNameEqualsTo(string lastName)   {     return c => c.LastName == lastName;   } } And then, use it with the repository. repository.Retrieve<Customer>(    CustomerQueries.LastNameEqualsTo("foo"),    c => c.Orders.SubExpand(o => o.Items));

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  • Monitoring Html Element CSS Changes in JavaScript

    - by Rick Strahl
    [ updated Feb 15, 2011: Added event unbinding to avoid unintended recursion ] Here's a scenario I've run into on a few occasions: I need to be able to monitor certain CSS properties on an HTML element and know when that CSS element changes. For example, I have a some HTML element behavior plugins like a drop shadow that attaches to any HTML element, but I then need to be able to automatically keep the shadow in sync with the window if the  element dragged around the window or moved via code. Unfortunately there's no move event for HTML elements so you can't tell when it's location changes. So I've been looking around for some way to keep track of the element and a specific CSS property, but no luck. I suspect there's nothing native to do this so the only way I could think of is to use a timer and poll rather frequently for the property. I ended up with a generic jQuery plugin that looks like this: (function($){ $.fn.watch = function (props, func, interval, id) { /// <summary> /// Allows you to monitor changes in a specific /// CSS property of an element by polling the value. /// when the value changes a function is called. /// The function called is called in the context /// of the selected element (ie. this) /// </summary> /// <param name="prop" type="String">CSS Properties to watch sep. by commas</param> /// <param name="func" type="Function"> /// Function called when the value has changed. /// </param> /// <param name="interval" type="Number"> /// Optional interval for browsers that don't support DOMAttrModified or propertychange events. /// Determines the interval used for setInterval calls. /// </param> /// <param name="id" type="String">A unique ID that identifies this watch instance on this element</param> /// <returns type="jQuery" /> if (!interval) interval = 200; if (!id) id = "_watcher"; return this.each(function () { var _t = this; var el$ = $(this); var fnc = function () { __watcher.call(_t, id) }; var itId = null; var data = { id: id, props: props.split(","), func: func, vals: [props.split(",").length], fnc: fnc, origProps: props, interval: interval }; $.each(data.props, function (i) { data.vals[i] = el$.css(data.props[i]); }); el$.data(id, data); hookChange(el$, id, data.fnc); }); function hookChange(el$, id, fnc) { el$.each(function () { var el = $(this); if (typeof (el.get(0).onpropertychange) == "object") el.bind("propertychange." + id, fnc); else if ($.browser.mozilla) el.bind("DOMAttrModified." + id, fnc); else itId = setInterval(fnc, interval); }); } function __watcher(id) { var el$ = $(this); var w = el$.data(id); if (!w) return; var _t = this; if (!w.func) return; // must unbind or else unwanted recursion may occur el$.unwatch(id); var changed = false; var i = 0; for (i; i < w.props.length; i++) { var newVal = el$.css(w.props[i]); if (w.vals[i] != newVal) { w.vals[i] = newVal; changed = true; break; } } if (changed) w.func.call(_t, w, i); // rebind event hookChange(el$, id, w.fnc); } } $.fn.unwatch = function (id) { this.each(function () { var el = $(this); var fnc = el.data(id).fnc; try { if (typeof (this.onpropertychange) == "object") el.unbind("propertychange." + id, fnc); else if ($.browser.mozilla) el.unbind("DOMAttrModified." + id, fnc); else clearInterval(id); } // ignore if element was already unbound catch (e) { } }); return this; } })(jQuery); With this I can now monitor movement by monitoring say the top CSS property of the element. The following code creates a box and uses the draggable (jquery.ui) plugin and a couple of custom plugins that center and create a shadow. Here's how I can set this up with the watcher: $("#box") .draggable() .centerInClient() .shadow() .watch("top", function() { $(this).shadow(); },70,"_shadow"); ... $("#box") .unwatch("_shadow") .shadow("remove"); This code basically sets up the window to be draggable and initially centered and then a shadow is added. The .watch() call then assigns a CSS property to monitor (top in this case) and a function to call in response. The component now sets up a setInterval call and keeps on pinging this property every time. When the top value changes the supplied function is called. While this works and I can now drag my window around with the shadow following suit it's not perfect by a long shot. The shadow move is delayed and so drags behind the window, but using a higher timer value is not appropriate either as the UI starts getting jumpy if the timer's set with too small of an increment. This sort of monitor can be useful for other things as well where operations are maybe not quite as time critical as a UI operation taking place. Can anybody see a better a better way of capturing movement of an element on the page?© Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET  JavaScript  jQuery  

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  • We've completed the first iteration

    - by CliveT
    There are a lot of features in C# that are implemented by the compiler and not by the underlying platform. One such feature is a lambda expression. Since local variables cannot be accessed once the current method activation finishes, the compiler has to go out of its way to generate a new class which acts as a home for any variable whose lifetime needs to be extended past the activation of the procedure. Take the following example:     Random generator = new Random();     Func func = () = generator.Next(10); In this case, the compiler generates a new class called c_DisplayClass1 which is marked with the CompilerGenerated attribute. [CompilerGenerated] private sealed class c__DisplayClass1 {     // Fields     public Random generator;     // Methods     public int b__0()     {         return this.generator.Next(10);     } } Two quick comments on this: (i)    A display was the means that compilers for languages like Algol recorded the various lexical contours of the nested procedure activations on the stack. I imagine that this is what has led to the name. (ii)    It is a shame that the same attribute is used to mark all compiler generated classes as it makes it hard to figure out what they are being used for. Indeed, you could imagine optimisations that the runtime could perform if it knew that classes corresponded to certain high level concepts. We can see that the local variable generator has been turned into a field in the class, and the body of the lambda expression has been turned into a method of the new class. The code that builds the Func object simply constructs an instance of this class and initialises the fields to their initial values.     c__DisplayClass1 class2 = new c__DisplayClass1();     class2.generator = new Random();     Func func = new Func(class2.b__0); Reflector already contains code to spot this pattern of code and reproduce the form containing the lambda expression, so this is example is correctly decompiled. The use of compiler generated code is even more spectacular in the case of iterators. C# introduced the idea of a method that could automatically store its state between calls, so that it can pick up where it left off. The code can express the logical flow with yield return and yield break denoting places where the method should return a particular value and be prepared to resume.         {             yield return 1;             yield return 2;             yield return 3;         } Of course, there was already a .NET pattern for expressing the idea of returning a sequence of values with the computation proceeding lazily (in the sense that the work for the next value is executed on demand). This is expressed by the IEnumerable interface with its Current property for fetching the current value and the MoveNext method for forcing the computation of the next value. The sequence is terminated when this method returns false. The C# compiler links these two ideas together so that an IEnumerator returning method using the yield keyword causes the compiler to produce the implementation of an Iterator. Take the following piece of code.         IEnumerable GetItems()         {             yield return 1;             yield return 2;             yield return 3;         } The compiler implements this by defining a new class that implements a state machine. This has an integer state that records which yield point we should go to if we are resumed. It also has a field that records the Current value of the enumerator and a field for recording the thread. This latter value is used for optimising the creation of iterator instances. [CompilerGenerated] private sealed class d__0 : IEnumerable, IEnumerable, IEnumerator, IEnumerator, IDisposable {     // Fields     private int 1__state;     private int 2__current;     public Program 4__this;     private int l__initialThreadId; The body gets converted into the code to construct and initialize this new class. private IEnumerable GetItems() {     d__0 d__ = new d__0(-2);     d__.4__this = this;     return d__; } When the class is constructed we set the state, which was passed through as -2 and the current thread. public d__0(int 1__state) {     this.1__state = 1__state;     this.l__initialThreadId = Thread.CurrentThread.ManagedThreadId; } The state needs to be set to 0 to represent a valid enumerator and this is done in the GetEnumerator method which optimises for the usual case where the returned enumerator is only used once. IEnumerator IEnumerable.GetEnumerator() {     if ((Thread.CurrentThread.ManagedThreadId == this.l__initialThreadId)               && (this.1__state == -2))     {         this.1__state = 0;         return this;     } The state machine itself is implemented inside the MoveNext method. private bool MoveNext() {     switch (this.1__state)     {         case 0:             this.1__state = -1;             this.2__current = 1;             this.1__state = 1;             return true;         case 1:             this.1__state = -1;             this.2__current = 2;             this.1__state = 2;             return true;         case 2:             this.1__state = -1;             this.2__current = 3;             this.1__state = 3;             return true;         case 3:             this.1__state = -1;             break;     }     return false; } At each stage, the current value of the state is used to determine how far we got, and then we generate the next value which we return after recording the next state. Finally we return false from the MoveNext to signify the end of the sequence. Of course, that example was really simple. The original method body didn't have any local variables. Any local variables need to live between the calls to MoveNext and so they need to be transformed into fields in much the same way that we did in the case of the lambda expression. More complicated MoveNext methods are required to deal with resources that need to be disposed when the iterator finishes, and sometimes the compiler uses a temporary variable to hold the return value. Why all of this explanation? We've implemented the de-compilation of iterators in the current EAP version of Reflector (7). This contrasts with previous version where all you could do was look at the MoveNext method and try to figure out the control flow. There's a fair amount of things we have to do. We have to spot the use of a CompilerGenerated class which implements the Enumerator pattern. We need to go to the class and figure out the fields corresponding to the local variables. We then need to go to the MoveNext method and try to break it into the various possible states and spot the state transitions. We can then take these pieces and put them back together into an object model that uses yield return to show the transition points. After that Reflector can carry on optimising using its usual optimisations. The pattern matching is currently a little too sensitive to changes in the code generation, and we only do a limited analysis of the MoveNext method to determine use of the compiler generated fields. In some ways, it is a pity that iterators are compiled away and there is no metadata that reflects the original intent. Without it, we are always going to dependent on our knowledge of the compiler's implementation. For example, we have noticed that the Async CTP changes the way that iterators are code generated, so we'll have to do some more work to support that. However, with that warning in place, we seem to do a reasonable job of decompiling the iterators that are built into the framework. Hopefully, the EAP will give us a chance to find examples where we don't spot the pattern correctly or regenerate the wrong code, and we can improve things. Please give it a go, and report any problems.

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  • Loosely coupled .NET Cache Provider using Dependency Injection

    - by Rhames
    I have recently been reading the excellent book “Dependency Injection in .NET”, written by Mark Seemann. I do not generally buy software development related books, as I never seem to have the time to read them, but I have found the time to read Mark’s book, and it was time well spent I think. Reading the ideas around Dependency Injection made me realise that the Cache Provider code I wrote about earlier (see http://geekswithblogs.net/Rhames/archive/2011/01/10/using-the-asp.net-cache-to-cache-data-in-a-model.aspx) could be refactored to use Dependency Injection, which should produce cleaner code. The goals are to: Separate the cache provider implementation (using the ASP.NET data cache) from the consumers (loose coupling). This will also mean that the dependency on System.Web for the cache provider does not ripple down into the layers where it is being consumed (such as the domain layer). Provide a decorator pattern to allow a consumer of the cache provider to be implemented separately from the base consumer (i.e. if we have a base repository, we can decorate this with a caching version). Although I used the term repository, in reality the cache consumer could be just about anything. Use constructor injection to provide the Dependency Injection, with a suitable DI container (I use Castle Windsor). The sample code for this post is available on github, https://github.com/RobinHames/CacheProvider.git ICacheProvider In the sample code, the key interface is ICacheProvider, which is in the domain layer. 1: using System; 2: using System.Collections.Generic; 3:   4: namespace CacheDiSample.Domain 5: { 6: public interface ICacheProvider<T> 7: { 8: T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry); 9: IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry); 10: } 11: }   This interface contains two methods to retrieve data from the cache, either as a single instance or as an IEnumerable. the second paramerter is of type Func<T>. This is the method used to retrieve data if nothing is found in the cache. The ASP.NET implementation of the ICacheProvider interface needs to live in a project that has a reference to system.web, typically this will be the root UI project, or it could be a separate project. The key thing is that the domain or data access layers do not need system.web references adding to them. In my sample MVC application, the CacheProvider is implemented in the UI project, in a folder called “CacheProviders”: 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Web; 5: using System.Web.Caching; 6: using CacheDiSample.Domain; 7:   8: namespace CacheDiSample.CacheProvider 9: { 10: public class CacheProvider<T> : ICacheProvider<T> 11: { 12: public T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry) 13: { 14: return FetchAndCache<T>(key, retrieveData, absoluteExpiry, relativeExpiry); 15: } 16:   17: public IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry) 18: { 19: return FetchAndCache<IEnumerable<T>>(key, retrieveData, absoluteExpiry, relativeExpiry); 20: } 21:   22: #region Helper Methods 23:   24: private U FetchAndCache<U>(string key, Func<U> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry) 25: { 26: U value; 27: if (!TryGetValue<U>(key, out value)) 28: { 29: value = retrieveData(); 30: if (!absoluteExpiry.HasValue) 31: absoluteExpiry = Cache.NoAbsoluteExpiration; 32:   33: if (!relativeExpiry.HasValue) 34: relativeExpiry = Cache.NoSlidingExpiration; 35:   36: HttpContext.Current.Cache.Insert(key, value, null, absoluteExpiry.Value, relativeExpiry.Value); 37: } 38: return value; 39: } 40:   41: private bool TryGetValue<U>(string key, out U value) 42: { 43: object cachedValue = HttpContext.Current.Cache.Get(key); 44: if (cachedValue == null) 45: { 46: value = default(U); 47: return false; 48: } 49: else 50: { 51: try 52: { 53: value = (U)cachedValue; 54: return true; 55: } 56: catch 57: { 58: value = default(U); 59: return false; 60: } 61: } 62: } 63:   64: #endregion 65:   66: } 67: }   The FetchAndCache helper method checks if the specified cache key exists, if it does not, the Func<U> retrieveData method is called, and the results are added to the cache. Using Castle Windsor to register the cache provider In the MVC UI project (my application root), Castle Windsor is used to register the CacheProvider implementation, using a Windsor Installer: 1: using Castle.MicroKernel.Registration; 2: using Castle.MicroKernel.SubSystems.Configuration; 3: using Castle.Windsor; 4:   5: using CacheDiSample.Domain; 6: using CacheDiSample.CacheProvider; 7:   8: namespace CacheDiSample.WindsorInstallers 9: { 10: public class CacheInstaller : IWindsorInstaller 11: { 12: public void Install(IWindsorContainer container, IConfigurationStore store) 13: { 14: container.Register( 15: Component.For(typeof(ICacheProvider<>)) 16: .ImplementedBy(typeof(CacheProvider<>)) 17: .LifestyleTransient()); 18: } 19: } 20: }   Note that the cache provider is registered as a open generic type. Consuming a Repository I have an existing couple of repository interfaces defined in my domain layer: IRepository.cs 1: using System; 2: using System.Collections.Generic; 3:   4: using CacheDiSample.Domain.Model; 5:   6: namespace CacheDiSample.Domain.Repositories 7: { 8: public interface IRepository<T> 9: where T : EntityBase 10: { 11: T GetById(int id); 12: IList<T> GetAll(); 13: } 14: }   IBlogRepository.cs 1: using System; 2: using CacheDiSample.Domain.Model; 3:   4: namespace CacheDiSample.Domain.Repositories 5: { 6: public interface IBlogRepository : IRepository<Blog> 7: { 8: Blog GetByName(string name); 9: } 10: }   These two repositories are implemented in the DataAccess layer, using Entity Framework to retrieve data (this is not important though). One important point is that in the BaseRepository implementation of IRepository, the methods are virtual. This will allow the decorator to override them. The BlogRepository is registered in a RepositoriesInstaller, again in the MVC UI project. 1: using Castle.MicroKernel.Registration; 2: using Castle.MicroKernel.SubSystems.Configuration; 3: using Castle.Windsor; 4:   5: using CacheDiSample.Domain.CacheDecorators; 6: using CacheDiSample.Domain.Repositories; 7: using CacheDiSample.DataAccess; 8:   9: namespace CacheDiSample.WindsorInstallers 10: { 11: public class RepositoriesInstaller : IWindsorInstaller 12: { 13: public void Install(IWindsorContainer container, IConfigurationStore store) 14: { 15: container.Register(Component.For<IBlogRepository>() 16: .ImplementedBy<BlogRepository>() 17: .LifestyleTransient() 18: .DependsOn(new 19: { 20: nameOrConnectionString = "BloggingContext" 21: })); 22: } 23: } 24: }   Now I can inject a dependency on the IBlogRepository into a consumer, such as a controller in my sample code: 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Web; 5: using System.Web.Mvc; 6:   7: using CacheDiSample.Domain.Repositories; 8: using CacheDiSample.Domain.Model; 9:   10: namespace CacheDiSample.Controllers 11: { 12: public class HomeController : Controller 13: { 14: private readonly IBlogRepository blogRepository; 15:   16: public HomeController(IBlogRepository blogRepository) 17: { 18: if (blogRepository == null) 19: throw new ArgumentNullException("blogRepository"); 20:   21: this.blogRepository = blogRepository; 22: } 23:   24: public ActionResult Index() 25: { 26: ViewBag.Message = "Welcome to ASP.NET MVC!"; 27:   28: var blogs = blogRepository.GetAll(); 29:   30: return View(new Models.HomeModel { Blogs = blogs }); 31: } 32:   33: public ActionResult About() 34: { 35: return View(); 36: } 37: } 38: }   Consuming the Cache Provider via a Decorator I used a Decorator pattern to consume the cache provider, this means my repositories follow the open/closed principle, as they do not require any modifications to implement the caching. It also means that my controllers do not have any knowledge of the caching taking place, as the DI container will simply inject the decorator instead of the root implementation of the repository. The first step is to implement a BlogRepository decorator, with the caching logic in it. Note that this can reside in the domain layer, as it does not require any knowledge of the data access methods. BlogRepositoryWithCaching.cs 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Text; 5:   6: using CacheDiSample.Domain.Model; 7: using CacheDiSample.Domain; 8: using CacheDiSample.Domain.Repositories; 9:   10: namespace CacheDiSample.Domain.CacheDecorators 11: { 12: public class BlogRepositoryWithCaching : IBlogRepository 13: { 14: // The generic cache provider, injected by DI 15: private ICacheProvider<Blog> cacheProvider; 16: // The decorated blog repository, injected by DI 17: private IBlogRepository parentBlogRepository; 18:   19: public BlogRepositoryWithCaching(IBlogRepository parentBlogRepository, ICacheProvider<Blog> cacheProvider) 20: { 21: if (parentBlogRepository == null) 22: throw new ArgumentNullException("parentBlogRepository"); 23:   24: this.parentBlogRepository = parentBlogRepository; 25:   26: if (cacheProvider == null) 27: throw new ArgumentNullException("cacheProvider"); 28:   29: this.cacheProvider = cacheProvider; 30: } 31:   32: public Blog GetByName(string name) 33: { 34: string key = string.Format("CacheDiSample.DataAccess.GetByName.{0}", name); 35: // hard code 5 minute expiry! 36: TimeSpan relativeCacheExpiry = new TimeSpan(0, 5, 0); 37: return cacheProvider.Fetch(key, () => 38: { 39: return parentBlogRepository.GetByName(name); 40: }, 41: null, relativeCacheExpiry); 42: } 43:   44: public Blog GetById(int id) 45: { 46: string key = string.Format("CacheDiSample.DataAccess.GetById.{0}", id); 47:   48: // hard code 5 minute expiry! 49: TimeSpan relativeCacheExpiry = new TimeSpan(0, 5, 0); 50: return cacheProvider.Fetch(key, () => 51: { 52: return parentBlogRepository.GetById(id); 53: }, 54: null, relativeCacheExpiry); 55: } 56:   57: public IList<Blog> GetAll() 58: { 59: string key = string.Format("CacheDiSample.DataAccess.GetAll"); 60:   61: // hard code 5 minute expiry! 62: TimeSpan relativeCacheExpiry = new TimeSpan(0, 5, 0); 63: return cacheProvider.Fetch(key, () => 64: { 65: return parentBlogRepository.GetAll(); 66: }, 67: null, relativeCacheExpiry) 68: .ToList(); 69: } 70: } 71: }   The key things in this caching repository are: I inject into the repository the ICacheProvider<Blog> implementation, via the constructor. This will make the cache provider functionality available to the repository. I inject the parent IBlogRepository implementation (which has the actual data access code), via the constructor. This will allow the methods implemented in the parent to be called if nothing is found in the cache. I override each of the methods implemented in the repository, including those implemented in the generic BaseRepository. Each override of these methods follows the same pattern. It makes a call to the CacheProvider.Fetch method, and passes in the parentBlogRepository implementation of the method as the retrieval method, to be used if nothing is present in the cache. Configuring the Caching Repository in the DI Container The final piece of the jigsaw is to tell Castle Windsor to use the BlogRepositoryWithCaching implementation of IBlogRepository, but to inject the actual Data Access implementation into this decorator. This is easily achieved by modifying the RepositoriesInstaller to use Windsor’s implicit decorator wiring: 1: using Castle.MicroKernel.Registration; 2: using Castle.MicroKernel.SubSystems.Configuration; 3: using Castle.Windsor; 4:   5: using CacheDiSample.Domain.CacheDecorators; 6: using CacheDiSample.Domain.Repositories; 7: using CacheDiSample.DataAccess; 8:   9: namespace CacheDiSample.WindsorInstallers 10: { 11: public class RepositoriesInstaller : IWindsorInstaller 12: { 13: public void Install(IWindsorContainer container, IConfigurationStore store) 14: { 15:   16: // Use Castle Windsor implicit wiring for the block repository decorator 17: // Register the outermost decorator first 18: container.Register(Component.For<IBlogRepository>() 19: .ImplementedBy<BlogRepositoryWithCaching>() 20: .LifestyleTransient()); 21: // Next register the IBlogRepository inmplementation to inject into the outer decorator 22: container.Register(Component.For<IBlogRepository>() 23: .ImplementedBy<BlogRepository>() 24: .LifestyleTransient() 25: .DependsOn(new 26: { 27: nameOrConnectionString = "BloggingContext" 28: })); 29: } 30: } 31: }   This is all that is needed. Now if the consumer of the repository makes a call to the repositories method, it will be routed via the caching mechanism. You can test this by stepping through the code, and seeing that the DataAccess.BlogRepository code is only called if there is no data in the cache, or this has expired. The next step is to add the SQL Cache Dependency support into this pattern, this will be a future post.

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  • Creating Property Set Expression Trees In A Developer Friendly Way

    - by Paulo Morgado
    In a previous post I showed how to create expression trees to set properties on an object. The way I did it was not very developer friendly. It involved explicitly creating the necessary expressions because the compiler won’t generate expression trees with property or field set expressions. Recently someone contacted me the help develop some kind of command pattern framework that used developer friendly lambdas to generate property set expression trees. Simply putting, given this entity class: public class Person { public string Name { get; set; } } The person in question wanted to write code like this: var et = Set((Person p) => p.Name = "me"); Where et is the expression tree that represents the property assignment. So, if we can’t do this, let’s try the next best thing that is splitting retrieving the property information from the retrieving the value to assign o the property: var et = Set((Person p) => p.Name, () => "me"); And this is something that the compiler can handle. The implementation of Set receives an expression to retrieve the property information from and another expression the retrieve the value to assign to the property: public static Expression<Action<TEntity>> Set<TEntity, TValue>( Expression<Func<TEntity, TValue>> propertyGetExpression, Expression<Func<TValue>> valueExpression) The implementation of this method gets the property information form the body of the property get expression (propertyGetExpression) and the value expression (valueExpression) to build an assign expression and builds a lambda expression using the same parameter of the property get expression as its parameter: public static Expression<Action<TEntity>> Set<TEntity, TValue>( Expression<Func<TEntity, TValue>> propertyGetExpression, Expression<Func<TValue>> valueExpression) { var entityParameterExpression = (ParameterExpression)(((MemberExpression)(propertyGetExpression.Body)).Expression); return Expression.Lambda<Action<TEntity>>( Expression.Assign(propertyGetExpression.Body, valueExpression.Body), entityParameterExpression); } And now we can use the expression to translate to another context or just compile and use it: var et = Set((Person p) => p.Name, () => name); Console.WriteLine(person.Name); // Prints: p => (p.Name = “me”) var d = et.Compile(); d(person); Console.WriteLine(person.Name); // Prints: me It can even support closures: var et = Set((Person p) => p.Name, () => name); Console.WriteLine(person.Name); // Prints: p => (p.Name = value(<>c__DisplayClass0).name) var d = et.Compile(); name = "me"; d(person); Console.WriteLine(person.Name); // Prints: me name = "you"; d(person); Console.WriteLine(person.Name); // Prints: you Not so useful in the intended scenario (but still possible) is building an expression tree that receives the value to assign to the property as a parameter: public static Expression<Action<TEntity, TValue>> Set<TEntity, TValue>(Expression<Func<TEntity, TValue>> propertyGetExpression) { var entityParameterExpression = (ParameterExpression)(((MemberExpression)(propertyGetExpression.Body)).Expression); var valueParameterExpression = Expression.Parameter(typeof(TValue)); return Expression.Lambda<Action<TEntity, TValue>>( Expression.Assign(propertyGetExpression.Body, valueParameterExpression), entityParameterExpression, valueParameterExpression); } This new expression can be used like this: var et = Set((Person p) => p.Name); Console.WriteLine(person.Name); // Prints: (p, Param_0) => (p.Name = Param_0) var d = et.Compile(); d(person, "me"); Console.WriteLine(person.Name); // Prints: me d(person, "you"); Console.WriteLine(person.Name); // Prints: you The only caveat is that we need to be able to write code to read the property in order to write to it.

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  • Using a Predicate as a key to a Dictionary

    - by Tom Hines
    I really love Linq and Lambda Expressions in C#.  I also love certain community forums and programming websites like DaniWeb. A user on DaniWeb posted a question about comparing the results of a game that is like poker (5-card stud), but is played with dice. The question stemmed around determining what was the winning hand.  I looked at the question and issued some comments and suggestions toward a potential answer, but I thought it was a neat homework exercise. [A little explanation] I eventually realized not only could I compare the results of the hands (by name) with a certain construct – I could also compare the values of the individual dice with the same construct. That piece of code eventually became a Dictionary with the KEY as a Predicate<int> and the Value a Func<T> that returns a string from the another structure that contains the mapping of an ENUM to a string.  In one instance, that string is the name of the hand and in another instance, it is a string (CSV) representation of of the digits in the hand. An added benefit is that the digits re returned in the order they would be for a proper poker hand.  For instance the hand 1,2,5,3,1 would be returned as ONE_PAIR (1,1,5,3,2). [Getting to the point] 1: using System; 2: using System.Collections.Generic; 3:   4: namespace DicePoker 5: { 6: using KVP_E2S = KeyValuePair<CDicePoker.E_DICE_POKER_HAND_VAL, string>; 7: public partial class CDicePoker 8: { 9: /// <summary> 10: /// Magical construction to determine the winner of given hand Key/Value. 11: /// </summary> 12: private static Dictionary<Predicate<int>, Func<List<KVP_E2S>, string>> 13: map_prd2fn = new Dictionary<Predicate<int>, Func<List<KVP_E2S>, string>> 14: { 15: {new Predicate<int>(i => i.Equals(0)), PlayerTie},//first tie 16:   17: {new Predicate<int>(i => i > 0), 18: (m => string.Format("Player One wins\n1={0}({1})\n2={2}({3})", 19: m[0].Key, m[0].Value, m[1].Key, m[1].Value))}, 20:   21: {new Predicate<int>(i => i < 0), 22: (m => string.Format("Player Two wins\n2={2}({3})\n1={0}({1})", 23: m[0].Key, m[0].Value, m[1].Key, m[1].Value))}, 24:   25: {new Predicate<int>(i => i.Equals(0)), 26: (m => string.Format("Tie({0}) \n1={1}\n2={2}", 27: m[0].Key, m[0].Value, m[1].Value))} 28: }; 29: } 30: } When this is called, the code calls the Invoke method of the predicate to return a bool.  The first on matching true will have its value invoked. 1: private static Func<DICE_HAND, E_DICE_POKER_HAND_VAL> GetHandEval = dh => 2: map_dph2fn[map_dph2fn.Keys.Where(enm2fn => enm2fn(dh)).First()]; After coming up with this process, I realized (with a little modification) it could be called to evaluate the individual values in the dice hand in the event of a tie. 1: private static Func<List<KVP_E2S>, string> PlayerTie = lst_kvp => 2: map_prd2fn.Skip(1) 3: .Where(x => x.Key.Invoke(RenderDigits(dhPlayerOne).CompareTo(RenderDigits(dhPlayerTwo)))) 4: .Select(s => s.Value) 5: .First().Invoke(lst_kvp); After that, I realized I could now create a program completely without “if” statements or “for” loops! 1: static void Main(string[] args) 2: { 3: Dictionary<Predicate<int>, Action<Action<string>>> main = new Dictionary<Predicate<int>, Action<Action<string>>> 4: { 5: {(i => i.Equals(0)), PlayGame}, 6: {(i => true), Usage} 7: }; 8:   9: main[main.Keys.Where(m => m.Invoke(args.Length)).First()].Invoke(Display); 10: } …and there you have it. :) ZIPPED Project

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  • Fading in/Fade out text in IE

    - by tau
    I had a problem and whipped up a quick solution: fade-in and fade-out a series of quotations. My solution works just as I want it in every browser except any of the IEs. The only problem with the IEs is that the text does not fade in and fade out; the text simply pops into existence. I believe I've run into a similar problem before when trying to dynamically change the filter:alpha(opacity=xx) of an element. Any help is greatly appreciated! <html> <head> <style> .fadetext{ background:green; border:1px solid red; height:50px; width:500px; } .fadetext div{ background:yellow; } </style> <script type="text/javascript"> var CI_common = { C:function(cls,elm){ if(!elm) elm = document; if(document.getElementsByClassName){ return elm.getElementsByClassName(cls); }else{ var t = []; var o = elm.getElementsByTagName("*"); var r = new RegExp("(^|\\s)" + cls + "($|\\s)"); for(var i=0;i<o.length;i++){ if(o[i].className.match(r)) t.push(o[i]); } return t; } }, eventAdd:function(obj,evt,func){ if(obj.addEventListener){ obj.addEventListener(evt,func,false); }else if(obj.attachEvent){ obj["x" + evt + func] = func; obj[evt + func] = function(){ obj["x" + evt + func](window.event); } obj.attachEvent("on" + evt,obj[evt + func]); } } } var CI_fadetext = { init:function(){ var c = CI_common.C("fadetext"); // Simply a getElementsByClassName function for(var i=0;i<c.length;i++){ c[i].style.overflow = "hidden"; var kids = c[i].getElementsByTagName("div"); for(var j=0;j<kids.length;j++){ kids[j].style.display = "none"; kids[j].style.filter = "alpha(opacity=0)"; kids[j].style.opacity = "0"; (function(obj,index,len){ obj.fadetexttimeout = setTimeout(function(){ CI_fadetext.fade(obj,true); obj.fadeininterval = setInterval(function(){ CI_fadetext.fade(obj,true); },5000*len) },5000*index); setTimeout(function(){ CI_fadetext.fade(obj,false); obj.fadeoutinterval = setInterval(function(){ CI_fadetext.fade(obj,false); },5000*len) },5000*index+4400); })(kids[j],j,kids.length); } } }, fade:function(elm,dir){ function fade(start){ start = (dir ? start + 10 : start - 10); elm.style.filter = "alpha(opacity=" + start + ")"; elm.style.opacity = start/100; document.getElementById("output").innerHTML = elm.style.filter; if(start > 100 || start <0){ elm.style.display = (dir ? "" : "none"); elm.style.filter = "alpha(opacity=" + (dir ? 100 : 0) + ")"; elm.style.opacity = (dir ? 1 : 0); }else elm.fadetexttimeout = setTimeout(function(){fade(start);},50); } if(dir){ elm.style.display = ""; fade(0); }else fade(100); } } CI_common.eventAdd(window,"load",CI_fadetext.init); // Just a window.onload level 2 event listener </script> </head> <body> <div id="output"></div> <div class="fadetext"> <div>AAAA</div> <div>BBBB</div> <div>CCCC</div> <div>DDDD</div> <div>EEEE</div> </div> </body> </html>

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  • The lua stack overflow,is this a bug?

    - by xiayong
    Some days ago, our program crash. I found the crash in lua code. So I check lua code, found the stack overflow. Please look this code In function luaD_precall: 1 if (!cl->isC) { /* Lua function? prepare its call */ 2 CallInfo *ci; 3 StkId st, base; 4 Proto *p = cl->p; 5 luaD_checkstack(L, p->maxstacksize); 6 func = restorestack(L, funcr); 7 if (!p->is_vararg) { /* no varargs? */ 8 base = func + 1; 9 if (L->top > base + p->numparams) 10 L->top = base + p->numparams; 11 } 12 else { /* vararg function */ 13 int nargs = cast_int(L->top - func) - 1; 14 base = adjust_varargs(L, p, nargs); 15 func = restorestack(L, funcr); /* previous call may change the stack */ 16 } 17 ci = inc_ci(L); /* now `enter' new function */ 18 ci->func = func; 19 L->base = ci->base = base; 20 ci->top = L->base + p->maxstacksize; 21 lua_assert(ci->top <= L->stack_last); 22 L->savedpc = p->code; /* starting point */ 23 ci->tailcalls = 0; 24 ci->nresults = nresults; 25 for (st = L->top; st < ci->top; st++) 26 setnilvalue(st); 27 L->top = ci->top; In my program, the p->maxstacksize is 79 before line 5, the current stacksize is 51, after call luaD_checkstack, the stacksize grow to 130. The lua function use vararg, so will run to line 14. Function adjust_varargs will be called. static StkId adjust_varargs (lua_State *L, Proto *p, int actual) { int i; int nfixargs = p->numparams; Table *htab = NULL; StkId base, fixed; for (; actual < nfixargs; ++actual) setnilvalue(L->top++); #if defined(LUA_COMPAT_VARARG) if (p->is_vararg & VARARG_NEEDSARG) { /* compat. with old-style vararg? */ int nvar = actual - nfixargs; /* number of extra arguments */ lua_assert(p->is_vararg & VARARG_HASARG); luaC_checkGC(L); htab = luaH_new(L, nvar, 1); /* create `arg' table */ In function adjust_varargs(), the lua function use “arg”, So luaC_checkGC will be called. In luaC_checkGC, the current lua stack size will be reduce to 65! The call stack like this: luaC_step() singlestep() propagatemark() traversestack() checkstacksizes() luaD_reallocstack() But the p->maxstacksize is 79, the stacksize is not enough… When the program run to line 27,the L->top is bigger than L->stack_last, in the next operation, will cause crash!

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  • LINQ: Enhancing Distinct With The PredicateEqualityComparer

    - by Paulo Morgado
    Today I was writing a LINQ query and I needed to select distinct values based on a comparison criteria. Fortunately, LINQ’s Distinct method allows an equality comparer to be supplied, but, unfortunately, sometimes, this means having to write custom equality comparer. Because I was going to need more than one equality comparer for this set of tools I was building, I decided to build a generic equality comparer that would just take a custom predicate. Something like this: public class PredicateEqualityComparer<T> : EqualityComparer<T> { private Func<T, T, bool> predicate; public PredicateEqualityComparer(Func<T, T, bool> predicate) : base() { this.predicate = predicate; } public override bool Equals(T x, T y) { if (x != null) { return ((y != null) && this.predicate(x, y)); } if (y != null) { return false; } return true; } public override int GetHashCode(T obj) { if (obj == null) { return 0; } return obj.GetHashCode(); } } Now I can write code like this: .Distinct(new PredicateEqualityComparer<Item>((x, y) => x.Field == y.Field)) But I felt that I’d lost all conciseness and expressiveness of LINQ and it doesn’t support anonymous types. So I came up with another Distinct extension method: public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source, Func<TSource, TSource, bool> predicate) { return source.Distinct(new PredicateEqualityComparer<TSource>(predicate)); } And the query is now written like this: .Distinct((x, y) => x.Field == y.Field) Looks a lot better, doesn’t it?

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