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• C/C++: Passing a structure by value, with another structure as one of its members, changes values of

  - by jellyfisharepretty

  Sorry for the confusing title, but it basically says it all. Here's the structures I'm using (found in OpenCV) : struct CV_EXPORTS CvRTParams : public CvDTreeParams { bool calc_var_importance; int nactive_vars; CvTermCriteria term_crit; CvRTParams() : CvDTreeParams( 5, 10, 0, false, 10, 0, false, false, 0 ), calc_var_importance(false), nactive_vars(0) { term_crit = cvTermCriteria( CV_TERMCRIT_ITER+CV_TERMCRIT_EPS, 50, 0.1 ); } } and typedef struct CvTermCriteria { int type; int max_iter; double epsilon; } CvTermCriteria; CV_INLINE CvTermCriteria cvTermCriteria( int type, int max_iter, double epsilon ) { CvTermCriteria t; t.type = type; t.max_iter = max_iter; t.epsilon = (float)epsilon; return t; } Now, I initialize a CvRTParams structure and set values for its members : CvRTParams params; params.max_depth = 8; params.min_sample_count = 10; params.regression_accuracy = 0; params.use_surrogates = false; params.max_categories = 10; params.priors = priors; params.calc_var_importance = true; params.nactive_vars = 9; params.term_crit.max_iter = 33; params.term_crit.epsilon = 0.1; params.term_crit.type = 3; Then call a function of an object, taking params in as a parameter : CvRTrees* rt = new CvRTrees; rt->train(t, CV_ROW_SAMPLE, r, 0, 0, var_type, 0, params) What happens now ? Values of... params.term_crit.max_iter params.term_crit.epsilon params.term_crit.type have changed ! They are no longer 33, 0.1 and 3, but something along the lines of 3, 7.05541e-313 and 4, and this, for the whole duration of the CvRtrees::train() function...

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• How to make 2 incompatible types, but with the same members, interchangeable?

  - by Quigrim

  Yesterday 2 of the guys on our team came to me with an uncommon problem. We are using a third-party component in one of our winforms applications. All the code has already been written against it. They then wanted to incorporate another third-party component, by the same vender, into our application. To their delight they found that the second component had the exact same public members as the first. But to their dismay, the 2 components have completely separate inheritance hierarchies, and implement no common interfaces. Makes you wonder... Well, makes me wonder. An example of the problem: public class ThirdPartyClass1 { public string Name { get { return "ThirdPartyClass1"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass1 is doing its thing."); } } public class ThirdPartyClass2 { public string Name { get { return "ThirdPartyClass2"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass2 is doing its thing."); } } Gladly they felt copying and pasting the code they wrote for the first component was not the correct answer. So they were thinking of assigning the component instant into an object reference and then modifying the code to do conditional casts after checking what type it was. But that is arguably even uglier than the copy and paste approach. So they then asked me if I can write some reflection code to access the properties and call the methods off the two different object types since we know what they are, and they are exactly the same. But my first thought was that there goes the elegance. I figure there has to be a better, graceful solution to this problem.

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• SQL select statement from 2 tables

  - by Steven

  Hi, I have a small sql question. I have 2 tables Members and Managers Members has: memberID, Name, Address Managers has: memberID, EditRights, DeleteRights EditRights and DeleteRights are of type bit. Mangers have a relationship with Members, because they are members themselves. I want to select all members id's, name and adress and for the members that are managers show if they have editrights and/or deleterights. SO: Exmaple data Members: ID, Name, Address 1, tom, 2 flat 2, dan, 3 flat 3, ben, 4 flat 4, bob, 6 flat 5, sam, 9 flat Managers: ID, Editrights, deleterights 2, 0, 1 4, 1, 1 5, 0, 0 I would like to display a select like this: 1, tom, 2 flat, no rights 2, dan, 3 flat, Delete 3, ben, 4 flat, no rights 4, bob, 6 flat, Edit&Delete 5, sam, 9 flat, no rights Any help would be great

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• Django many-to-many relationship to self with extra data, how do I select from a certain direction?

  - by Jake

  I have some hierarchical data where each Set can have many members and can belong to more than one Set(group) Here are the models: class Set(models.Model): ... groups = models.ManyToManyField('self', through='Membership', symmetrical=False) members = models.ManyToManyField('self', through='Membership', symmetrical=False) class Membership(models.Model): group = models.ForeignKey( Set, related_name='Members' ) member = models.ForeignKey( Set, related_name='Groups' ) order = models.IntegerField( default=-1 ) I want to know how to get all the members or all the groups for a Set instance. I think I can do it as follows, but it's not very logical, can anyone tell me what's going on and how I should be doing it? # This gives me a set of Sets # Which seems to be the groups this Set belongs to set_instance.set_set.all() # These give me a set of Memberships, not Sets set_instance.Members.all() set_instance.Groups.all() # These they both return a set of Sets # which seem to be the members of this one set_instance.members.all() set_instance.groups.all()

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• Joining two select queries and ordering results

  - by user1

  Basically I'm just unsure as to why this query is failing to execute: (SELECT replies.reply_post, replies.reply_content, replies.reply_date AS d, members.username FROM (replies) AS a INNER JOIN members ON replies.reply_by = members.id) UNION (SELECT posts.post_id, posts.post_title, posts.post_date AS d, members.username FROM (posts) as b WHERE posts.post_set = 0 INNER JOIN members ON posts.post_by = members.id) ORDER BY d DESC LIMIT 5 I'm getting this error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'a INNER JOIN members ON replies.re' at line 2 All I'm trying to do is select the 5 most recent rows (dates) from these two tables. I've tried Join, union etc and I've seen numerous queries where people have put another query after the FROM statement and that just makes no logical sense to me as to how that works? Am I safe to say that you can join the same table from two different but joined queries? Or am I taking completely the wrong approach, because frankly I can't seem see how this query is failing despite reading the error message. (The two queries on there own work fine)

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• Welcome to the newly merged JCP EC!

  - by Heather VanCura

  As part of the JCP.Next effort, the second JSR as part of the JCP program reforms, JSR 355, Executive Committee (EC) Merge, will take effect on Tuesday as JCP 2.9. The first in the effort was JSR 348, which took effect as JCP 2.8 in October 2011. EC members guide the evolution of the Java technologies by approving and voting on all technology proposals (Java Specification Requests, or JSRs). They are also responsible for defining the JCP's rules of governance and the legal agreement between members and the organization. They provide guidance to the Program Management Office (PMO) and they represent the interests of the JCP to the broader community. Starting on Tuesday, 13 November, JCP 2.9 is in effect, and the EC is merged from two ECs -- one representing Java SE/EE and one representing Java ME -- to one merged EC. IBM and Oracle each gave up one of their two seats (one per EC) and the terms expired for four members who did not run for re-election: AT&T, Deutsch Telekom, Siemens and Vodafone. All four remain JCP members. In addition, the seat occupied by RIM was forfeited due to lack of participation in October 2012. The JCP values the organizations and representatives for their contribution to the JCP EC, and looks forward to their continued participation in the JCP Program. The complete listing of the EC, 24 members total at the moment, is now available. We asked the two newcomers to the EC, Cinterion and CloudBees, and the re-elected London Java Community, to comment on their plans for their term in the EC. Read about their plans in the article published on JCP.org, "JCP 2.9 with a Merged EC Takes Effect 13 November". Also, plan to attend the public (open to all community members) EC Meeting planned for 20 November at 15:00 PST.  Details will be posted here and on the JCP.org home page next week.

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• Using web.config directory security and extensionless urls

  - by Matt Brailsford

  Hi Guys, I'd like to use the built in directory security features built into the web.config to restrict access to child pages of a parent page. My structure is as follows: Members Members/News Members/Press Members/Movies Users should be able to have access to the members parent page, but not child pages. My problem is, because I am using extensionless URLs, the web.config thinks this is a directory and so access is blocked. Is there a way to say only restrict access for sub pages?

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• django display m2m elements in a template

  - by dana

  if a have a declaration like theclass = Classroom.objects.get(classname = classname) members = theclass.members.all() and i want to display all the members(of a class) in a template, how should i do it?? if i write: {{theclass.members.all}} the output is an empty list(though the class has some members) How should the elements of a m2m table be displayed in a template? thanks!

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• Anatomy of a serialization killer

  - by Brian Donahue

  As I had mentioned last month, I have been working on a project to create an easy-to-use managed debugger. It's still an internal tool that we use at Red Gate as part of product support to analyze application errors on customer's computers, and as such, should be easy to use and not require installation. Since the project has got rather large and important, I had decided to use SmartAssembly to protect all of my hard work. This was trivial for the most part, but the loading and saving of results was broken by SA after using the obfuscation, rendering the loading and saving of XML results basically useless, although the merging and error reporting was an absolute godsend and definitely worth the price of admission. (Well, I get my Red Gate licenses for free, but you know what I mean!)My initial reaction was to simply exclude the serializable results class and all of its' members from obfuscation, and that was just dandy, but a few weeks on I decided to look into exactly why serialization had broken and change the code to work with SA so I could write any new code to be compatible with SmartAssembly and save me some additional testing and changes to the SA project.In simple terms, SA does all that it can to prevent serialization problems, for instance, it will not obfuscate public members of a DLL and it will exclude any types with the Serializable attribute from obfuscation. This prevents public members and properties from being made private and having the name changed. If the serialization is done inside the executable, however, public members have the access changed to private and are renamed. That was my first problem, because my types were in the executable assembly and implemented ISerializable, but did not have the Serializable attribute set on them!public class RedFlagResults : ISerializable        {        }The second problem caused by the pruning feature. Although RedFlagResults had public members, they were not truly properties, and used the GetObjectData() method of ISerializable to serialize the members. For that reason, SA could not exclude these members from pruning and further broke the serialization. public class RedFlagResults : ISerializable        {                public List<RedFlag.Exception> Exceptions;                 #region ISerializable Members                 public void GetObjectData(SerializationInfo info, StreamingContext context)                {                                info.AddValue("Exceptions", Exceptions);                }                 #endregionSo to fix this, it was necessary to make Exceptions a proper property by implementing get and set on it. Also, I added the Serializable attribute so that I don't have to exclude the class from obfuscation in the SA project any more. The DoNotPrune attribute means I do not need to exclude the class from pruning.[Serializable, SmartAssembly.Attributes.DoNotPrune]        public class RedFlagResults        {                public List<RedFlag.Exception> Exceptions {get;set;}        }Similarly, the Exception class gets the Serializable and DoNotPrune attributes applied so all of its' properties are excluded from obfuscation.Now my project has some protection from prying eyes by scrambling up the code so it's harder to reverse-engineer, without breaking anything. SmartAssembly has also provided the benefit of merging so that the end-user doesn't need to extract all of the DLL files needed by RedFlag into a directory, and can be run directly from the .zip archive. When an error occurs (hey, I'm only human!), an exception report can be sent to me so I can see what went wrong without having to, er, debug the debugger.

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• Implicit and Explicit implementations for Multiple Interface inheritance

  Following C#.NET demo explains you all the scenarios for implementation of Interface methods to classes. There are two ways you can implement a interface method to a class. 1. Implicit Implementation 2. Explicit Implementation. Please go though the sample. using System;   namespace ImpExpTest { class Program { static void Main(string[] args) { C o3 = new C(); Console.WriteLine(o3.fu());   I1 o1 = new C(); Console.WriteLine(o1.fu());   I2 o2 = new C(); Console.WriteLine(o2.fu());   var o4 = new C(); //var is considered as C Console.WriteLine(o4.fu());   var o5 = (I1)new C(); //var is considered as I1 Console.WriteLine(o5.fu());   var o6 = (I2)new C(); //var is considered as I2 Console.WriteLine(o6.fu());   D o7 = new D(); Console.WriteLine(o7.fu());   I1 o8 = new D(); Console.WriteLine(o8.fu());   I2 o9 = new D(); Console.WriteLine(o9.fu()); } }   interface I1 { string fu(); }   interface I2 { string fu(); }   class C : I1, I2 { #region Imicitly Defined I1 Members public string fu() { return "Hello C"; } #endregion Imicitly Defined I1 Members   #region Explicitly Defined I1 Members   string I1.fu() { return "Hello from I1"; }   #endregion Explicitly Defined I1 Members   #region Explicitly Defined I2 Members   string I2.fu() { return "Hello from I2"; }   #endregion Explicitly Defined I2 Members }   class D : C { #region Imicitly Defined I1 Members public string fu() { return "Hello from D"; } #endregion Imicitly Defined I1 Members } }.csharpcode, .csharpcode pre{ font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em;}.csharpcode .lnum { color: #606060; }Output:-Hello C Hello from I1 Hello from I2 Hello C Hello from I1 Hello from I2 Hello from D Hello from I1 Hello from I2 span.fullpost {display:none;}

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• Oracle Announces New Oracle Exastack Program for ISV Partners

  - by pfolgado

  Oracle Exastack Program Enables ISV Partners to Leverage a Scalable, Integrated Infrastructure to Deliver Their Applications Tuned and Optimized for High-Performance News Facts Enabling Independent Software Vendors (ISVs) and other members of Oracle Partner Network (OPN) to rapidly build and deliver faster, more reliable applications to end customers, Oracle today introduced Oracle Exastack Ready, available now, and Oracle Exastack Optimized, available in fall 2011 through OPN. The Oracle Exastack Program focuses on helping ISVs run their solutions on Oracle Exadata Database Machine and Oracle Exalogic Elastic Cloud -- integrated systems in which the software and hardware are engineered to work together. These products provide partners with a lower cost and high performance infrastructure for database and application workloads across on-premise and cloud based environments. Leveraging the new Oracle Exastack Program in which applications can qualify as Oracle Exastack Ready or Oracle Exastack Optimized, partners can use available OPN resources to optimize their applications to run faster and more reliably -- providing increased performance to their end users. By deploying their applications on Oracle Exadata Database Machine and Oracle Exalogic Elastic Cloud, ISVs can reduce the cost, time and support complexities typically associated with building and maintaining a disparate application infrastructure -- enabling them to focus more on their core competencies, accelerating innovation and delivering superior value to customers. After qualifying their applications as Oracle Exastack Ready, partners can note to customers that their applications run on and support Oracle Exadata Database Machine and Oracle Exalogic Elastic Cloud component products including Oracle Solaris, Oracle Linux, Oracle Database and Oracle WebLogic Server. Customers can be confident when choosing a partner's Oracle Exastack Optimized application, knowing it has been tuned by the OPN member on Oracle Exadata Database Machine or Oracle Exalogic Elastic Cloud with a goal of delivering optimum speed, scalability and reliability. Partners participating in the Oracle Exastack Program can also leverage their Oracle Exastack Ready and Oracle Exastack Optimized applications to advance to Platinum or Diamond level in OPN. Oracle Exastack Programs Provide ISVs a Reliable, High-Performance Application Infrastructure With the Oracle Exastack Program ISVs have several options to qualify and tune their applications with Oracle Exastack, including: Oracle Exastack Ready: Oracle Exastack Ready provides qualifying partners with specific branding and promotional benefits based on their adoption of Oracle products. If a partner application supports the latest major release of one of these products, the partner may use the corresponding logo with their product marketing materials: Oracle Solaris Ready, Oracle Linux Ready, Oracle Database Ready, and Oracle WebLogic Ready. Oracle Exastack Ready is available to OPN members at the Gold level or above. Additionally, OPN members participating in the program can leverage their Oracle Exastack Ready applications toward advancement to the Platinum or Diamond levels in the OPN Specialized program and toward achieving Oracle Exastack Optimized status. Oracle Exastack Optimized: When available, for OPN members at the Gold level or above, Oracle Exastack Optimized will provide direct access to Oracle technical resources and dedicated Oracle Exastack lab environments so OPN members can test and tune their applications to deliver optimal performance and scalability on Oracle Exadata Database Machine or Oracle Exalogic Elastic Cloud. Oracle Exastack Optimized will provide OPN members with specific branding and promotional benefits including the use of the Oracle Exastack Optimized logo. OPN members participating in the program will also be able to leverage their Oracle Exastack Optimized applications toward advancement to Platinum or Diamond level in the OPN Specialized program. Oracle Exastack Labs and ISV Enablement: Dedicated Oracle Exastack lab environments and related technical enablement resources (including Guided Learning Paths and Boot Camps) will be available through OPN for OPN members to further their knowledge of Oracle Exastack offerings, and qualify their applications for Oracle Exastack Optimized or Oracle Exastack Ready. Oracle Exastack labs will be available to qualifying OPN members at the Gold level or above. Partners are eligible to participate in the Oracle Exastack Ready program immediately, which will help them meet the requirements to attain Oracle Exastack Optimized status in the future. Guidelines for Oracle Exastack Optimized, as well as Oracle Exastack Labs will be available in fall 2011. Supporting Quotes "In order to effectively differentiate their software applications in the marketplace, ISVs need to rapidly deliver new capabilities and performance improvements," said Judson Althoff, Oracle senior vice president of Worldwide Alliances and Channels and Embedded Sales. "With Oracle Exastack, ISVs have the ability to optimize and deploy their applications with a complete, integrated and cloud-ready infrastructure that will help them accelerate innovation, unlock new features and functionality, and deliver superior value to customers." "We view performance as absolutely critical and a key differentiator," said Tom Stock, SVP of Product Management, GoldenSource. "As a leading provider of enterprise data management solutions for securities and investment management firms, with Oracle Exadata Database Machine, we see an opportunity to notably improve data processing performance -- providing high quality 'golden copy' data in a reduced timeframe. Achieving Oracle Exastack Optimized status will be a stamp of approval that our solution will provide the performance and scalability that our customers demand." "As a leading provider of Revenue Intelligence solutions for telecommunications, media and entertainment service providers, our customers continually demand more readily accessible, enriched and pre-analyzed information to minimize their financial risks and maximize their margins," said Alon Aginsky, President and CEO of cVidya Networks. "Oracle Exastack enables our solutions to deliver the power, infrastructure, and innovation required to transform our customers' business operations and stay ahead of the game." Supporting Resources Oracle PartnerNetwork (OPN) Oracle Exastack Oracle Exastack Datasheet Judson Althoff blog Connect with the Oracle Partner community at OPN on Facebook, OPN on LinkedIn, OPN on YouTube, or OPN on Twitter

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• object / class methods serialized as well?

  - by Mat90

  I know that data members are saved to disk but I was wondering whether object's/class' methods are saved in binary format as well? Because I found some contradictionary info, for example: Ivor Horton: "Class objects contain function members as well as data members, and all the members, both data and functions, have access specifiers; therefore, to record objects in an external file, the information written to the file must contain complete specifications of all the class structures involved." and: Are methods also serialized along with the data members in .NET? Thus: are method's assembly instructions (opcodes and operands) stored to disk as well? Just like a precompiled LIB or DLL? During the DOS ages I used assembly so now and then. As far as I remember from Delphi and the following site (answer by dan04): Are methods also serialized along with the data members in .NET? sizeof(<OBJECT or CLASS>) will give the size of all data members together (no methods/procedures). Also a nice C example is given there with data and members declared in one class/struct but at runtime these methods are separate procedures acting on a struct of data. However, I think that later class/object implementations like Pascal's VMT may be different in memory.

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• Dynamic Types and DynamicObject References in C#

  - by Rick Strahl

  I've been working a bit with C# custom dynamic types for several customers recently and I've seen some confusion in understanding how dynamic types are referenced. This discussion specifically centers around types that implement IDynamicMetaObjectProvider or subclass from DynamicObject as opposed to arbitrary type casts of standard .NET types. IDynamicMetaObjectProvider types  are treated special when they are cast to the dynamic type. Assume for a second that I've created my own implementation of a custom dynamic type called DynamicFoo which is about as simple of a dynamic class that I can think of:public class DynamicFoo : DynamicObject { Dictionary<string, object> properties = new Dictionary<string, object>(); public string Bar { get; set; } public DateTime Entered { get; set; } public override bool TryGetMember(GetMemberBinder binder, out object result) { result = null; if (!properties.ContainsKey(binder.Name)) return false; result = properties[binder.Name]; return true; } public override bool TrySetMember(SetMemberBinder binder, object value) { properties[binder.Name] = value; return true; } } This class has an internal dictionary member and I'm exposing this dictionary member through a dynamic by implementing DynamicObject. This implementation exposes the properties dictionary so the dictionary keys can be referenced like properties (foo.NewProperty = "Cool!"). I override TryGetMember() and TrySetMember() which are fired at runtime every time you access a 'property' on a dynamic instance of this DynamicFoo type. Strong Typing and Dynamic Casting I now can instantiate and use DynamicFoo in a couple of different ways: Strong TypingDynamicFoo fooExplicit = new DynamicFoo(); var fooVar = new DynamicFoo(); These two commands are essentially identical and use strong typing. The compiler generates identical code for both of them. The var statement is merely a compiler directive to infer the type of fooVar at compile time and so the type of fooExplicit is DynamicFoo, just like fooExplicit. This is very static - nothing dynamic about it - and it completely ignores the IDynamicMetaObjectProvider implementation of my class above as it's never used. Using either of these I can access the native properties:DynamicFoo fooExplicit = new DynamicFoo();// static typing assignmentsfooVar.Bar = "Barred!"; fooExplicit.Entered = DateTime.Now; // echo back static values Console.WriteLine(fooVar.Bar); Console.WriteLine(fooExplicit.Entered); but I have no access whatsoever to the properties dictionary. Basically this creates a strongly typed instance of the type with access only to the strongly typed interface. You get no dynamic behavior at all. The IDynamicMetaObjectProvider features don't kick in until you cast the type to dynamic. If I try to access a non-existing property on fooExplicit I get a compilation error that tells me that the property doesn't exist. Again, it's clearly and utterly non-dynamic. Dynamicdynamic fooDynamic = new DynamicFoo(); fooDynamic on the other hand is created as a dynamic type and it's a completely different beast. I can also create a dynamic by simply casting any type to dynamic like this:DynamicFoo fooExplicit = new DynamicFoo(); dynamic fooDynamic = fooExplicit; Note that dynamic typically doesn't require an explicit cast as the compiler automatically performs the cast so there's no need to use as dynamic. Dynamic functionality works at runtime and allows for the dynamic wrapper to look up and call members dynamically. A dynamic type will look for members to access or call in two places: Using the strongly typed members of the object Using theIDynamicMetaObjectProvider Interface methods to access members So rather than statically linking and calling a method or retrieving a property, the dynamic type looks up - at runtime  - where the value actually comes from. It's essentially late-binding which allows runtime determination what action to take when a member is accessed at runtime *if* the member you are accessing does not exist on the object. Class members are checked first before IDynamicMetaObjectProvider interface methods are kick in. All of the following works with the dynamic type:dynamic fooDynamic = new DynamicFoo(); // dynamic typing assignments fooDynamic.NewProperty = "Something new!"; fooDynamic.LastAccess = DateTime.Now; // dynamic assigning static properties fooDynamic.Bar = "dynamic barred"; fooDynamic.Entered = DateTime.Now; // echo back dynamic values Console.WriteLine(fooDynamic.NewProperty); Console.WriteLine(fooDynamic.LastAccess); Console.WriteLine(fooDynamic.Bar); Console.WriteLine(fooDynamic.Entered); The dynamic type can access the native class properties (Bar and Entered) and create and read new ones (NewProperty,LastAccess) all using a single type instance which is pretty cool. As you can see it's pretty easy to create an extensible type this way that can dynamically add members at runtime dynamically. The Alter Ego of IDynamicObject The key point here is that all three statements - explicit, var and dynamic - declare a new DynamicFoo(), but the dynamic declaration results in completely different behavior than the first two simply because the type has been cast to dynamic. Dynamic binding means that the type loses its typical strong typing, compile time features. You can see this easily in the Visual Studio code editor. As soon as you assign a value to a dynamic you lose Intellisense and you see which means there's no Intellisense and no compiler type checking on any members you apply to this instance. If you're new to the dynamic type it might seem really confusing that a single type can behave differently depending on how it is cast, but that's exactly what happens when you use a type that implements IDynamicMetaObjectProvider. Declare the type as its strong type name and you only get to access the native instance members of the type. Declare or cast it to dynamic and you get dynamic behavior which accesses native members plus it uses IDynamicMetaObjectProvider implementation to handle any missing member definitions by running custom code. You can easily cast objects back and forth between dynamic and the original type:dynamic fooDynamic = new DynamicFoo(); fooDynamic.NewProperty = "New Property Value"; DynamicFoo foo = fooDynamic; foo.Bar = "Barred"; Here the code starts out with a dynamic cast and a dynamic assignment. The code then casts back the value to the DynamicFoo. Notice that when casting from dynamic to DynamicFoo and back we typically do not have to specify the cast explicitly - the compiler can induce the type so I don't need to specify as dynamic or as DynamicFoo. Moral of the Story This easy interchange between dynamic and the underlying type is actually super useful, because it allows you to create extensible objects that can expose non-member data stores and expose them as an object interface. You can create an object that hosts a number of strongly typed properties and then cast the object to dynamic and add additional dynamic properties to the same type at runtime. You can easily switch back and forth between the strongly typed instance to access the well-known strongly typed properties and to dynamic for the dynamic properties added at runtime. Keep in mind that dynamic object access has quite a bit of overhead and is definitely slower than strongly typed binding, so if you're accessing the strongly typed parts of your objects you definitely want to use a strongly typed reference. Reserve dynamic for the dynamic members to optimize your code. The real beauty of dynamic is that with very little effort you can build expandable objects or objects that expose different data stores to an object interface. I'll have more on this in my next post when I create a customized and extensible Expando object based on DynamicObject.© Rick Strahl, West Wind Technologies, 2005-2012Posted in CSharp  .NET   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Is it possible to Take object members directly from a queue of type object?

  - by Luke Mcneice

  Hi all, If I where to have a Queue holding a collection of objects (Custom object,bool,bool,bool,bool) and the custom object holds three doubles itself. Can I use the .Take(IntegerValue) command to only take one of the doubles (for the specified take length) from the custom entity contained in the queue and cast it to a double array, possibly with the .ToArray<double> function? Thanks, Luke

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• Android: Context menu doesn't show up for ListView with members defined by LinearLayout?

  - by RandomEngy

  I've got a ListActivity and ListView and I've bound some data to it. The data shows up fine, and I've also registered a context menu for the view. When I display the list items as just a simple TextView, it works fine: <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/nametext" android:layout_width="wrap_content" android:layout_height="wrap_content"/> However when I try something a bit more complex, like show the name and a CheckBox, the menu never shows up: <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content" android:orientation="horizontal"> <TextView android:id="@+id/nametext" android:layout_width="wrap_content" android:layout_height="wrap_content"/> <CheckBox android:id="@+id/namecheckbox" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> Can long-presses work on more complex elements? I'm building on 2.1.

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• Is it a bad idea to have different team members on Visual Studio 2008 and 2010?

  - by MCS

  I'm about to start working on a C# project. I'd like to buy VS 2010, but the only other member of the programming team is already using VS 2008. I'm concerned that having two different versions of VS in use will cause code compatibility issues. Is this a valid concern?

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• What is the correct less operator for simple class with two int members?

  - by Frank

  What is the correct operator< for the following class? struct Foo { int x; int y; friend bool operator<(const Foo&, const Foo&); }; Thanks!

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• Dealing with ArrayLists in java...all members of the arraylist updating themselves?

  - by Charlie

  I have a function that shrinks the size of a "Food bank" (represented by a rectangle in my GUI) once some of the food has been taken. I have the following function check for this: public boolean tryToPickUpFood(Ant a) { int xCoord = a.getLocation().x; int yCoord = a.getLocation().y; for (int i = 0; i < foodPiles.size(); i++) { if (foodPiles.get(i).containsPoint(xCoord, yCoord)) { foodPiles.get(i).decreaseFood(); return true; } } return false; } Where decreaseFood shrinks the rectangle.. public void decreaseFood() { foodAmount -= 1; shrinkPile(); } private void shrinkPile() { WIDTH -=1; HEIGHT = WIDTH; } However, whenever one rectangle shrinks, ALL of the rectangles shrink. Why would this be?

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• Why do pure virtual base classes get direct access to static data members while derived instances do

  - by Shamster

  I've created a simple pair of classes. One is pure virtual with a static data member, and the other is derived from the base, as follows: #include <iostream> template <class T> class Base { public: Base (const T _member) { member = _member; } static T member; virtual void Print () const = 0; }; template <class T> T Base<T>::member; template <class T> void Base<T>::Print () const { std::cout << "Base: " << member << std::endl; } template <class T> class Derived : public Base<T> { public: Derived (const T _member) : Base<T>(_member) { } virtual void Print () const { std::cout << "Derived: " << this->member << std::endl; } }; I've found from this relationship that when I need access to the static data member in the base class, I can call it with direct access as if it were a regular, non-static class member. i.e. - the Base::Print() method does not require a this- modifier. However, the derived class does require the this-member indirect access syntax. I don't understand why this is. Both class methods are accessing the same static data, so why does the derived class need further specification? A simple call to test it is: int main () { Derived<double> dd (7.0); dd.Print(); return 0; } which prints the expected "Derived: 7"

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• How to access static members in a Velocity template?

  - by matt b

  I'm not sure if there is a way to do this in Velocity or not: I have a User POJO which a property named Status, which looks like an enum (but it is not, since I am stuck on Java 1.4), the definition looks something like this: public class User { // default status to User private Status status = Status.USER; public void setStatus(Status status) { this.status = status; } public Status getStatus() { return status; } And Status is a static inner class: public static final class Status { private String statusString; private Status(String statusString) { this.statusString = statusString; } public final static Status USER = new Status("user"); public final static Status ADMIN = new Status("admin"); public final static Status STATUS_X = new Status("blah"); //.equals() and .hashCode() implemented as well } With this pattern, a user status can easily be tested in a conditional such as if(User.Status.ADMIN.equals(user.getStatus())) ... ... without having to reference any constants for the status ID, any magic numbers, etc. However, I can't figure out how to test these conditionals in my Velocity template with VTL. I'd like to just print a simple string based upon the user's status, such as: Welcome <b>${user.name}</b>! <br/> <br/> #if($user.status == com.company.blah.User.Status.USER) You are a regular user #elseif($user.status == com.company.blah.User.Status.ADMIN) You are an administrator #etc... #end But this throws an Exception that looks like org.apache.velocity.exception.ParseErrorException: Encountered "User" at webpages/include/dashboard.inc[line 10, column 21] Was expecting one of: "[" ... From the VTL User Guide, there is no mention of accessing a Java class/static member directly in VTL, it appears that the right hand side (RHS) of a conditional can only be a number literal, string literal, property reference, or method reference. So is there any way that I can access static Java properties/references in a Velocity template? I'm aware that as a workaround, I could embed the status ID or some other identifier as a reference in my controller (this is a web MVC application using Velocity as the View technology), but I strongly do not want to embed any magic numbers or constants in the view layer.

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• C++0x: How can I access variadic tuple members by index at runtime?

  - by nonoitall

  I have written the following basic Tuple template: template <typename... T> class Tuple; template <uintptr_t N, typename... T> struct TupleIndexer; template <typename Head, typename... Tail> class Tuple<Head, Tail...> : public Tuple<Tail...> { private: Head element; public: template <uintptr_t N> typename TupleIndexer<N, Head, Tail...>::Type& Get() { return TupleIndexer<N, Head, Tail...>::Get(*this); } uintptr_t GetCount() const { return sizeof...(Tail) + 1; } private: friend struct TupleIndexer<0, Head, Tail...>; }; template <> class Tuple<> { public: uintptr_t GetCount() const { return 0; } }; template <typename Head, typename... Tail> struct TupleIndexer<0, Head, Tail...> { typedef Head& Type; static Type Get(Tuple<Head, Tail...>& tuple) { return tuple.element; } }; template <uintptr_t N, typename Head, typename... Tail> struct TupleIndexer<N, Head, Tail...> { typedef typename TupleIndexer<N - 1, Tail...>::Type Type; static Type Get(Tuple<Head, Tail...>& tuple) { return TupleIndexer<N - 1, Tail...>::Get(*(Tuple<Tail...>*) &tuple); } }; It works just fine, and I can access elements in array-like fashion by using tuple.Get<Index() - but I can only do that if I know the index at compile-time. However, I need to access elements in the tuple by index at runtime, and I won't know at compile-time which index needs to be accessed. Example: int chosenIndex = getUserInput(); cout << "The option you chose was: " << tuple.Get(chosenIndex) << endl; What's the best way to do this?

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• how to get access to private members of nested class?

  - by macias

  Background: I have enclosed (parent) class E with nested class N with several instances of N in E. In the enclosed (parent) class I am doing some calculations and I am setting the values for each instance of nested class. Something like this: n1.field1 = ...; n1.field2 = ...; n1.field3 = ...; n2.field1 = ...; ... It is one big eval method (in parent class). My intention is -- since all calculations are in parent class (they cannot be done per nested instance because it would make code more complicated) -- make the setters only available to parent class and getters public. And now there is a problem: when I make the setters private, parent class cannot acces them when I make them public, everybody can change the values and C# does not have friend concept I cannot pass values in constructor because lazy evaluation mechanism is used (so the instances have to be created when referencing them -- I create all objects and the calculation is triggered on demand) I am stuck -- how to do this (limit access up to parent class, no more, no less)? I suspect I'll get answer-question first -- "but why you don't split the evaluation per each field" -- so I answer this by example: how do you calculate min and max value of a collection? In a fast way? The answer is -- in one pass. This is why I have one eval function which does calculations and sets all fields at once.

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• Is a good practice to initialize private data members from within ctor by calling the associated pro

  - by yuko.aihara

  interface IAnimal { string Name { get; set; } } class Dog : IAnimal { private string name; public Dog(string name) { Name = name; } public string Name { get { return name; } set { name = value; } } }

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• How do I reflect over the members of dynamic object?

  - by Flatliner DOA

  I need to get a dictionary of properties and their values from an object declared with the dynamic keyword in .NET 4? It seems using reflection for this will not work. Example: dynamic s = new ExpandoObject(); s.Path = "/Home"; s.Name = "Home"; // How do I enumerate the Path and Name properties and get their values? IDictionary<string, object> propertyValues = ???

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